clang18/0011-Add-the-support-for-classic-flang.patch

From 3d36d3891f2a654d5ec2a0ce3c2ff47b597d1c42 Mon Sep 17 00:00:00 2001
From: luofeng14 <luofeng13@huawei.com>
Date: Mon, 11 Mar 2024 21:25:03 +0800
Subject: [PATCH] sync classic flang patch

---
 clang/CMakeLists.txt                          |    5 +
 clang/include/clang/Basic/CodeGenOptions.h    |    3 +
 .../clang/Basic/DiagnosticDriverKinds.td      |    6 +
 clang/include/clang/Basic/MacroBuilder.h      |    3 +-
 clang/include/clang/Basic/Sanitizers.def      |    2 +
 clang/include/clang/Driver/CMakeLists.txt     |   13 +-
 clang/include/clang/Driver/Options.td         |  197 ++-
 clang/include/clang/Driver/ToolChain.h        |   17 +
 clang/include/clang/Driver/Types.def          |    7 +
 clang/include/clang/Driver/Types.h            |    8 +
 clang/include/clang/Frontend/Utils.h          |   32 +
 clang/lib/CodeGen/BackendUtil.cpp             |    6 +
 clang/lib/CodeGen/CGDebugInfo.cpp             |   10 +-
 clang/lib/Driver/CMakeLists.txt               |    8 +-
 clang/lib/Driver/Driver.cpp                   |   60 +-
 clang/lib/Driver/OffloadBundler.cpp           |    4 +
 clang/lib/Driver/ToolChain.cpp                |   36 +-
 clang/lib/Driver/ToolChains/Clang.cpp         |   60 +
 clang/lib/Driver/ToolChains/ClassicFlang.cpp  | 1217 +++++++++++++++++
 clang/lib/Driver/ToolChains/ClassicFlang.h    |   49 +
 clang/lib/Driver/ToolChains/CommonArgs.cpp    |   69 +-
 clang/lib/Driver/ToolChains/CommonArgs.h      |   20 +
 clang/lib/Driver/ToolChains/Cuda.cpp          |   35 +
 clang/lib/Driver/ToolChains/Cuda.h            |    5 +
 clang/lib/Driver/ToolChains/Darwin.cpp        |    4 +
 clang/lib/Driver/ToolChains/Gnu.cpp           |    4 +
 clang/lib/Driver/ToolChains/Linux.cpp         |  190 +++
 clang/lib/Driver/ToolChains/Linux.h           |    5 +
 clang/lib/Driver/ToolChains/MSVC.cpp          |  115 ++
 clang/lib/Driver/ToolChains/MSVC.h            |   11 +
 clang/lib/Driver/ToolChains/MinGW.cpp         |    4 +
 clang/lib/Driver/Types.cpp                    |   50 +
 clang/lib/Frontend/InitPreprocessor.cpp       |   20 -
 clang/test/CMakeLists.txt                     |    1 +
 .../test/CodeGen/libpgmath-logfun-aarch64.ll  |   58 +
 clang/test/CodeGen/libpgmath-logfun-x86_64.ll |   57 +
 clang/test/Driver/autocomplete.c              |    2 +-
 clang/test/Driver/emit-flang-attrs.f90        |   58 +
 .../test/Driver/flang/Inputs/llvm-ir-input.ll |    0
 .../flang/classic-flang-emit-flang-llvm.f95   |   10 +
 .../flang/classic-flang-fp-contract.f95       |   27 +
 .../flang/classic-flang-must-preprocess.F     |   12 +
 .../flang/classic-flang-must-preprocess.F95   |   12 +
 .../test/Driver/flang/classic-flang-version.f |    3 +
 .../flang/classic-flang-vscale-mbits.f95      |   28 +
 .../Driver/flang/classic-flang-vscale.f95     |   28 +
 clang/test/Driver/flang/classic-flang.f       |   26 +
 clang/test/Driver/flang/classic-flang.f95     |  120 ++
 clang/test/Driver/flang/flang.f90             |    2 +
 clang/test/Driver/flang/flang_ucase.F90       |    2 +
 clang/test/Driver/flang/llvm-ir-input.f       |    7 +
 .../Driver/flang/multiple-inputs-mixed.f90    |    2 +
 clang/test/Driver/flang/multiple-inputs.f90   |    2 +
 clang/test/Driver/flang/reassoc.f90           |   59 +
 clang/test/Driver/fortran-phases.f90          |  119 ++
 clang/test/Driver/fortran-preprocessor.f90    |   48 +
 clang/test/Driver/fortran.f95                 |    2 +
 clang/test/Driver/gfortran.f90                |    1 +
 clang/test/Driver/lit.local.cfg               |    3 +
 clang/test/lit.cfg.py                         |    3 +
 clang/test/lit.site.cfg.py.in                 |    1 +
 clang/tools/driver/CMakeLists.txt             |    2 +-
 62 files changed, 2933 insertions(+), 37 deletions(-)
 create mode 100644 clang/lib/Driver/ToolChains/ClassicFlang.cpp
 create mode 100644 clang/lib/Driver/ToolChains/ClassicFlang.h
 mode change 100644 => 100755 clang/lib/Driver/Types.cpp
 create mode 100644 clang/test/CodeGen/libpgmath-logfun-aarch64.ll
 create mode 100644 clang/test/CodeGen/libpgmath-logfun-x86_64.ll
 create mode 100644 clang/test/Driver/emit-flang-attrs.f90
 create mode 100644 clang/test/Driver/flang/Inputs/llvm-ir-input.ll
 create mode 100644 clang/test/Driver/flang/classic-flang-emit-flang-llvm.f95
 create mode 100644 clang/test/Driver/flang/classic-flang-fp-contract.f95
 create mode 100644 clang/test/Driver/flang/classic-flang-must-preprocess.F
 create mode 100644 clang/test/Driver/flang/classic-flang-must-preprocess.F95
 create mode 100644 clang/test/Driver/flang/classic-flang-version.f
 create mode 100644 clang/test/Driver/flang/classic-flang-vscale-mbits.f95
 create mode 100644 clang/test/Driver/flang/classic-flang-vscale.f95
 create mode 100644 clang/test/Driver/flang/classic-flang.f
 create mode 100644 clang/test/Driver/flang/classic-flang.f95
 create mode 100644 clang/test/Driver/flang/llvm-ir-input.f
 create mode 100644 clang/test/Driver/flang/reassoc.f90
 create mode 100644 clang/test/Driver/fortran-phases.f90
 create mode 100644 clang/test/Driver/fortran-preprocessor.f90

diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
index d558b0522e82..949f12d3ce8c 100644
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -392,6 +392,11 @@ if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
   endif()
 endif()
 
+option(LLVM_ENABLE_CLASSIC_FLANG "Build support for classic Flang instead of the new built-in Flang" OFF)
+if(LLVM_ENABLE_CLASSIC_FLANG)
+  add_definitions( -DENABLE_CLASSIC_FLANG )
+endif()
+
 option(CLANG_BUILD_TOOLS
   "Build the Clang tools. If OFF, just generate build targets." ON)
 
diff --git a/clang/include/clang/Basic/CodeGenOptions.h b/clang/include/clang/Basic/CodeGenOptions.h
index 14fc94fe27f9..41577b97e030 100644
--- a/clang/include/clang/Basic/CodeGenOptions.h
+++ b/clang/include/clang/Basic/CodeGenOptions.h
@@ -59,6 +59,9 @@ public:
     Accelerate, // Use the Accelerate framework.
     LIBMVEC,    // GLIBC vector math library.
     MASSV,      // IBM MASS vector library.
+#ifdef ENABLE_CLASSIC_FLANG
+    PGMATH,     // PGI math library.
+#endif
     SVML,       // Intel short vector math library.
     SLEEF,      // SLEEF SIMD Library for Evaluating Elementary Functions.
     Darwin_libsystem_m, // Use Darwin's libsytem_m vector functions.
diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
index 1b69324d073a..09a1949d7596 100644
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -131,6 +131,10 @@ def err_drv_invalid_linker_name : Error<
   "invalid linker name in argument '%0'">;
 def err_drv_invalid_rtlib_name : Error<
   "invalid runtime library name in argument '%0'">;
+def err_drv_invalid_allocatable_mode : Error<
+  "invalid semantic mode for assignments to allocatables in argument '%0'">;
+def err_drv_unsupported_fixed_line_length : Error<
+  "unsupported fixed-format line length in argument '%0'">;
 def err_drv_unsupported_rtlib_for_platform : Error<
   "unsupported runtime library '%0' for platform '%1'">;
 def err_drv_invalid_unwindlib_name : Error<
@@ -354,6 +358,8 @@ def err_drv_negative_columns : Error<
   "invalid value '%1' in '%0', value must be 'none' or a positive integer">;
 def err_drv_small_columns : Error<
   "invalid value '%1' in '%0', value must be '%2' or greater">;
+def err_drv_clang_unsupported_minfo_arg : Error<
+  "'%0' option does not support '%1' value">;
 
 def err_drv_invalid_malign_branch_EQ : Error<
   "invalid argument '%0' to -malign-branch=; each element must be one of: %1">;
diff --git a/clang/include/clang/Basic/MacroBuilder.h b/clang/include/clang/Basic/MacroBuilder.h
index 96e67cbbfa3f..bfc5e38c15e3 100644
--- a/clang/include/clang/Basic/MacroBuilder.h
+++ b/clang/include/clang/Basic/MacroBuilder.h
@@ -24,9 +24,10 @@ class MacroBuilder {
   raw_ostream &Out;
 public:
   MacroBuilder(raw_ostream &Output) : Out(Output) {}
+  virtual ~MacroBuilder() {}
 
   /// Append a \#define line for macro of the form "\#define Name Value\n".
-  void defineMacro(const Twine &Name, const Twine &Value = "1") {
+  virtual void defineMacro(const Twine &Name, const Twine &Value = "1") {
     Out << "#define " << Name << ' ' << Value << '\n';
   }
 
diff --git a/clang/include/clang/Basic/Sanitizers.def b/clang/include/clang/Basic/Sanitizers.def
index c2137e3f61f6..4f0a2bf332ef 100644
--- a/clang/include/clang/Basic/Sanitizers.def
+++ b/clang/include/clang/Basic/Sanitizers.def
@@ -107,6 +107,8 @@ SANITIZER("signed-integer-overflow", SignedIntegerOverflow)
 SANITIZER("unreachable", Unreachable)
 SANITIZER("vla-bound", VLABound)
 SANITIZER("vptr", Vptr)
+// fortran contiguous pointer checks
+SANITIZER("discontiguous", Discontiguous)
 
 // IntegerSanitizer
 SANITIZER("unsigned-integer-overflow", UnsignedIntegerOverflow)
diff --git a/clang/include/clang/Driver/CMakeLists.txt b/clang/include/clang/Driver/CMakeLists.txt
index ea55ba0f1f27..8c0af1528a96 100644
--- a/clang/include/clang/Driver/CMakeLists.txt
+++ b/clang/include/clang/Driver/CMakeLists.txt
@@ -1,7 +1,14 @@
 set(LLVM_TARGET_DEFINITIONS Options.td)
+
+set(CLANG_DRIVER_OPTIONS)
 if (BUILD_FOR_OPENEULER)
-tablegen(LLVM Options.inc -gen-opt-parser-defs -DBUILD_FOR_OPENEULER)
-else()
-tablegen(LLVM Options.inc -gen-opt-parser-defs)
+   list(APPEND CLANG_DRIVER_OPTIONS -DBUILD_FOR_OPENEULER )
 endif()
+
+if (LLVM_ENABLE_CLASSIC_FLANG)
+   list(APPEND CLANG_DRIVER_OPTIONS -DENABLE_CLASSIC_FLANG )
+endif()
+ 
+tablegen(LLVM Options.inc ${CLANG_DRIVER_OPTIONS} -gen-opt-parser-defs  )
+
 add_public_tablegen_target(ClangDriverOptions)
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index d4f7315bf8cb..365285966a67 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -590,7 +590,11 @@ class InternalDriverOpt : Group<internal_driver_Group>,
   Flags<[NoXarchOption, HelpHidden]>;
 def driver_mode : Joined<["--"], "driver-mode=">, Group<internal_driver_Group>,
   Flags<[CoreOption, NoXarchOption, HelpHidden]>,
+#ifdef ENABLE_CLASSIC_FLANG
+  HelpText<"Set the driver mode to one of: 'gcc', 'g++', 'cpp', 'cl', or 'flang'">;
+#else
   HelpText<"Set the driver mode to either 'gcc', 'g++', 'cpp', or 'cl'">;
+#endif
 def rsp_quoting : Joined<["--"], "rsp-quoting=">, Group<internal_driver_Group>,
   Flags<[CoreOption, NoXarchOption, HelpHidden]>,
   HelpText<"Set the rsp quoting to either 'posix', or 'windows'">;
@@ -1183,6 +1187,10 @@ def d_Flag : Flag<["-"], "d">, Group<d_Group>;
 def d_Joined : Joined<["-"], "d">, Group<d_Group>;
 def emit_ast : Flag<["-"], "emit-ast">, Flags<[CoreOption]>,
   HelpText<"Emit Clang AST files for source inputs">;
+#ifdef ENABLE_CLASSIC_FLANG
+def emit_flang_llvm : Flag<["-"], "emit-flang-llvm">,
+  HelpText<"Emit Flang LLVM files for source inputs">;
+#endif
 def emit_llvm : Flag<["-"], "emit-llvm">, Flags<[CC1Option, FC1Option, FlangOption]>, Group<Action_Group>,
   HelpText<"Use the LLVM representation for assembler and object files">;
 def emit_interface_stubs : Flag<["-"], "emit-interface-stubs">, Flags<[CC1Option]>, Group<Action_Group>,
@@ -2640,10 +2648,17 @@ def fno_experimental_isel : Flag<["-"], "fno-experimental-isel">, Group<f_clang_
   Alias<fno_global_isel>;
 def fveclib : Joined<["-"], "fveclib=">, Group<f_Group>, Flags<[CC1Option]>,
     HelpText<"Use the given vector functions library">,
+#ifdef ENABLE_CLASSIC_FLANG
+    Values<"Accelerate,libmvec,MASSV,PGMATH,SVML,SLEEF,Darwin_libsystem_m,ArmPL,none">,
+    NormalizedValuesScope<"CodeGenOptions">,
+    NormalizedValues<["Accelerate", "LIBMVEC", "MASSV", "PGMATH", "SVML", "SLEEF",
+                      "Darwin_libsystem_m", "ArmPL", "NoLibrary"]>,
+#else
     Values<"Accelerate,libmvec,MASSV,SVML,SLEEF,Darwin_libsystem_m,ArmPL,none">,
     NormalizedValuesScope<"CodeGenOptions">,
     NormalizedValues<["Accelerate", "LIBMVEC", "MASSV", "SVML", "SLEEF",
                       "Darwin_libsystem_m", "ArmPL", "NoLibrary"]>,
+#endif
     MarshallingInfoEnum<CodeGenOpts<"VecLib">, "NoLibrary">;
 def fno_lax_vector_conversions : Flag<["-"], "fno-lax-vector-conversions">, Group<f_Group>,
   Alias<flax_vector_conversions_EQ>, AliasArgs<["none"]>;
@@ -5382,6 +5397,20 @@ def module_dir : JoinedOrSeparate<["-"], "module-dir">, MetaVarName<"<dir>">,
 It is also added to the list of directories to be searched by an USE statement.
 The default is the current directory.}]>;
 
+#ifdef ENABLE_CLASSIC_FLANG
+// Define a group for Fortran source format options.
+def fortran_format_Group : OptionGroup<"Fortran format Group">, Group<gfortran_Group>;
+def ffixed_form : Flag<["-"], "ffixed-form">, Group<fortran_format_Group>,
+  HelpText<"Process source files in fixed form">;
+def fno_fixed_form : Flag<["-"], "fno-fixed-form">, Group<fortran_format_Group>,
+  HelpText<"Disable fixed-form format for Fortran">;
+def ffree_form : Flag<["-"], "ffree-form">, Group<fortran_format_Group>,
+  HelpText<"Process source files in free form">;
+def fno_free_form : Flag<["-"], "fno-free-form">, Group<fortran_format_Group>,
+  HelpText<"Disable free-form format for Fortran">;
+def ffixed_line_length_VALUE : Joined<["-"], "ffixed-line-length-">, Group<f_Group>,
+  HelpText<"Set line length in fixed-form format Fortran, current supporting only 72 and 132 characters">;
+#else
 def ffixed_form : Flag<["-"], "ffixed-form">, Group<f_Group>,
   HelpText<"Process source files in fixed form">;
 def ffree_form : Flag<["-"], "ffree-form">, Group<f_Group>,
@@ -5391,6 +5420,7 @@ def ffixed_line_length_EQ : Joined<["-"], "ffixed-line-length=">, Group<f_Group>
   DocBrief<[{Set column after which characters are ignored in typical fixed-form lines in the source
 file}]>;
 def ffixed_line_length_VALUE : Joined<["-"], "ffixed-line-length-">, Group<f_Group>, Alias<ffixed_line_length_EQ>;
+#endif
 def fconvert_EQ : Joined<["-"], "fconvert=">, Group<f_Group>,
   HelpText<"Set endian conversion of data for unformatted files">;
 def fopenacc : Flag<["-"], "fopenacc">, Group<f_Group>,
@@ -5399,8 +5429,14 @@ def fdefault_double_8 : Flag<["-"],"fdefault-double-8">, Group<f_Group>,
   HelpText<"Set the default double precision kind to an 8 byte wide type">;
 def fdefault_integer_8 : Flag<["-"],"fdefault-integer-8">, Group<f_Group>,
   HelpText<"Set the default integer and logical kind to an 8 byte wide type">;
+#ifdef ENABLE_CLASSIC_FLANG
+def fno_default_integer_8 : Flag<["-"], "fno-default-integer-8">, Group<f_Group>;
+#endif
 def fdefault_real_8 : Flag<["-"],"fdefault-real-8">, Group<f_Group>,
   HelpText<"Set the default real kind to an 8 byte wide type">;
+#ifdef ENABLE_CLASSIC_FLANG
+def fno_default_real_8 : Flag<["-"], "fno-default-real-8">, Group<f_Group>;
+#endif
 def flarge_sizes : Flag<["-"],"flarge-sizes">, Group<f_Group>,
   HelpText<"Use INTEGER(KIND=8) for the result type in size-related intrinsics">;
 
@@ -5410,7 +5446,17 @@ def fintrinsic_modules_path : Separate<["-"], "fintrinsic-modules-path">,  Group
   HelpText<"Specify where to find the compiled intrinsic modules">,
   DocBrief<[{This option specifies the location of pre-compiled intrinsic modules,
   if they are not in the default location expected by the compiler.}]>;
-
+#ifdef ENABLE_CLASSIC_FLANG
+def fbackslash : Flag<["-"], "fbackslash">, Group<gfortran_Group>,
+  HelpText<"Specify that backslash in string introduces an escape character">,
+  DocBrief<[{Change the interpretation of backslashes in string literals from
+a single backslash character to "C-style" escape characters.}]>;
+def fno_backslash : Flag<["-"], "fno-backslash">, Group<gfortran_Group>;
+// Add the options -f(no-)implicit-none and -f(no-)automatic for compatibility
+// reason. They are not implemented yet in Classic Flang for now.
+defm implicit_none : BooleanFFlag<"implicit-none">, Group<gfortran_Group>;
+def fno_automatic : Flag<["-"], "fno-automatic">, Group<gfortran_Group>;
+#else
 defm backslash : OptInFC1FFlag<"backslash", "Specify that backslash in string introduces an escape character">;
 defm xor_operator : OptInFC1FFlag<"xor-operator", "Enable .XOR. as a synonym of .NEQV.">;
 defm logical_abbreviations : OptInFC1FFlag<"logical-abbreviations", "Enable logical abbreviations">;
@@ -5419,6 +5465,7 @@ defm underscoring : OptInFC1FFlag<"underscoring", "Appends one trailing undersco
 
 def fno_automatic : Flag<["-"], "fno-automatic">, Group<f_Group>,
   HelpText<"Implies the SAVE attribute for non-automatic local objects in subprograms unless RECURSIVE">;
+#endif
 
 defm stack_arrays : BoolOptionWithoutMarshalling<"f", "stack-arrays",
   PosFlag<SetTrue, [], "Attempt to allocate array temporaries on the stack, no matter their size">,
@@ -5426,12 +5473,19 @@ defm stack_arrays : BoolOptionWithoutMarshalling<"f", "stack-arrays",
 defm loop_versioning : BoolOptionWithoutMarshalling<"f", "version-loops-for-stride",
   PosFlag<SetTrue, [], "Create unit-strided versions of loops">,
    NegFlag<SetFalse, [], "Do not create unit-strided loops (default)">>;
+
 } // let Flags = [FC1Option, FlangOption, FlangOnlyOption]
 
+#ifdef ENABLE_CLASSIC_FLANG
+def J : JoinedOrSeparate<["-"], "J">,
+  Flags<[RenderJoined]>,
+  Group<gfortran_Group>;
+#else
 def J : JoinedOrSeparate<["-"], "J">,
   Flags<[RenderJoined, FlangOption, FC1Option, FlangOnlyOption]>,
   Group<gfortran_Group>,
   Alias<module_dir>;
+#endif
 
 //===----------------------------------------------------------------------===//
 // FC1 Options
@@ -7458,6 +7512,147 @@ def fcgl : DXCFlag<"fcgl">, Alias<emit_pristine_llvm>;
 def enable_16bit_types : DXCFlag<"enable-16bit-types">, Alias<fnative_half_type>,
   HelpText<"Enable 16-bit types and disable min precision types."
            "Available in HLSL 2018 and shader model 6.2.">;
+
+#ifdef ENABLE_CLASSIC_FLANG
+// Classic Flang options that we recognize in the driver and pass along when
+// invoking flang1/flang2 to compile Fortran code.
+def flang_rt_Group : OptionGroup<"Flang runtime library Group">;
+def pgi_fortran_Group : OptionGroup<"PGI Fortran compatibility Group">,
+  Flags<[HelpHidden]>;
+
+// Classic Flang-specific options
+multiclass BooleanKFlag<string name> {
+  def _on : Flag<["-"], "K"#name>;
+  def _off : Flag<["-"], "Kno"#name>;
+}
+
+multiclass BooleanMFlag<string name> {
+  def _on : Flag<["-"], "M"#name>;
+  def _off : Flag<["-"], "Mno"#name>;
+}
+
+def Mfixed : Flag<["-"], "Mfixed">, Group<fortran_format_Group>,
+  HelpText<"Force fixed-form format Fortran">,
+  Flags<[HelpHidden]>;
+def Mfree_on: Flag<["-"], "Mfree">, Group<fortran_format_Group>,
+  HelpText<"Enable free-form format for Fortran">,
+  Flags<[HelpHidden]>;
+def Mfree_off: Flag<["-"], "Mnofree">, Group<fortran_format_Group>,
+  HelpText<"Disable free-form format for Fortran">,
+  Flags<[HelpHidden]>;
+def Mfreeform_on: Flag<["-"], "Mfreeform">, Group<fortran_format_Group>,
+  HelpText<"Enable free-form format for Fortran">,
+  Flags<[HelpHidden]>;
+def Mfreeform_off: Flag<["-"], "Mnofreeform">, Group<fortran_format_Group>,
+  HelpText<"Disable free-form format for Fortran">,
+  Flags<[HelpHidden]>;
+
+def Minfo_EQ : CommaJoined<["-"], "Minfo=">,
+  HelpText<"Diagnostic information about successful optimizations">,
+  Values<"all,vect,inline">;
+def Minfoall : Flag<["-"], "Minfo">,
+  HelpText<"Diagnostic information about all successful optimizations">;
+def Mneginfo_EQ : CommaJoined<["-"], "Mneginfo=">,
+  HelpText<"Diagnostic information about missed optimizations">,
+  Values<"all,vect,inline">;
+def Mneginfoall : Flag<["-"], "Mneginfo">,
+  HelpText<"Diagnostic information about all missed optimizations">;
+
+def Mipa: Joined<["-"], "Mipa">, Group<pgi_fortran_Group>;
+def Mstackarrays: Joined<["-"], "Mstack_arrays">, Group<pgi_fortran_Group>;
+def pc: JoinedOrSeparate<["-"], "pc">, Group<pgi_fortran_Group>;
+def Mfprelaxed: Joined<["-"], "Mfprelaxed">, Group<pgi_fortran_Group>;
+def Mnofprelaxed: Joined<["-"], "Mnofprelaxed">, Group<pgi_fortran_Group>;
+defm Mstride0: BooleanMFlag<"stride0">, Group<pgi_fortran_Group>;
+defm Mrecursive: BooleanMFlag<"recursive">, Group<pgi_fortran_Group>;
+defm Mreentrant: BooleanMFlag<"reentrant">, Group<pgi_fortran_Group>;
+defm Mbounds: BooleanMFlag<"bounds">, Group<pgi_fortran_Group>;
+def Mdaz_on: Flag<["-"], "Mdaz">, Group<pgi_fortran_Group>,
+  HelpText<"Treat denormalized numbers as zero">;
+def Mdaz_off: Flag<["-"], "Mnodaz">, Group<pgi_fortran_Group>,
+  HelpText<"Disable treating denormalized numbers as zero">;
+def Kieee_on : Flag<["-"], "Kieee">, Group<pgi_fortran_Group>,
+  HelpText<"Enable IEEE division">;
+def Kieee_off : Flag<["-"], "Knoieee">, Group<pgi_fortran_Group>,
+  HelpText<"Disable IEEE division">;
+def Mextend : Flag<["-"], "Mextend">, Group<pgi_fortran_Group>,
+  HelpText<"Allow lines up to 132 characters in Fortran sources">;
+def Mpreprocess : Flag<["-"], "Mpreprocess">, Group<pgi_fortran_Group>,
+  HelpText<"Preprocess Fortran files">;
+def Mstandard: Flag<["-"], "Mstandard">, Group<pgi_fortran_Group>,
+  HelpText<"Check Fortran standard conformance">;
+def Mchkptr: Flag<["-"], "Mchkptr">, Group<pgi_fortran_Group>;
+def Mwritable_constants: Flag<["-"], "Mwritable-constants">, Group<pgi_fortran_Group>,
+  HelpText<"Store constants in the writable data segment">;
+defm Minline: BooleanMFlag<"inline">, Group<pgi_fortran_Group>;
+def fma: Flag<["-"], "fma">, Group<pgi_fortran_Group>,
+  HelpText<"Enable generation of FMA instructions">;
+def nofma: Flag<["-"], "nofma">, Group<pgi_fortran_Group>,
+  HelpText<"Disable generation of FMA instructions">;
+defm Mfma: BooleanMFlag<"fma">, Group<pgi_fortran_Group>,
+  HelpText<"Enable generation of FMA instructions">;
+def mp: Flag<["-"], "mp">, Group<pgi_fortran_Group>,
+  HelpText<"Enable OpenMP">;
+def nomp: Flag<["-"], "nomp">, Group<pgi_fortran_Group>,
+  HelpText<"Do not link with OpenMP library libomp">;
+def Mflushz_on: Flag<["-"], "Mflushz">, Group<pgi_fortran_Group>,
+  HelpText<"Set SSE to flush-to-zero mode">;
+def Mflushz_off: Flag<["-"], "Mnoflushz">, Group<pgi_fortran_Group>,
+  HelpText<"Disabling setting SSE to flush-to-zero mode">;
+def Msave_on: Flag<["-"], "Msave">, Group<pgi_fortran_Group>,
+  HelpText<"Assume all Fortran variables have SAVE attribute">;
+def Msave_off: Flag<["-"], "Mnosave">, Group<pgi_fortran_Group>,
+  HelpText<"Assume no Fortran variables have SAVE attribute">;
+def Mcache_align_on: Flag<["-"], "Mcache_align">, Group<pgi_fortran_Group>,
+  HelpText<"Align large objects on cache-line boundaries">;
+def Mcache_align_off: Flag<["-"], "Mnocache_align">, Group<pgi_fortran_Group>,
+  HelpText<"Disable aligning large objects on cache-line boundaries">;
+def ModuleDir : Separate<["-"], "module">, Group<pgi_fortran_Group>,
+  HelpText<"Fortran module path">;
+def Minform_EQ : Joined<["-"], "Minform=">,
+  HelpText<"Set error level of messages to display">;
+def Mallocatable_EQ : Joined<["-"], "Mallocatable=">,
+  HelpText<"Select semantics for assignments to allocatables (F03 or F95)">;
+def Mbyteswapio: Flag<["-"], "Mbyteswapio">, Group<pgi_fortran_Group>,
+  HelpText<"Swap byte-order for unformatted input/output">;
+def byteswapio: Flag<["-"], "byteswapio">, Group<gfortran_Group>,
+  HelpText<"Swap byte-order for unformatted input/output">;
+def Mbackslash: Flag<["-"], "Mbackslash">, Group<pgi_fortran_Group>,
+  HelpText<"Treat backslash like any other character in character strings">;
+def Mnobackslash: Flag<["-"], "Mnobackslash">, Group<pgi_fortran_Group>,
+  HelpText<"Treat backslash as C-style escape character">;
+def staticFlangLibs: Flag<["-"], "static-flang-libs">, Group<flang_rt_Group>,
+  HelpText<"Link using static Flang libraries">;
+def noFlangLibs: Flag<["-"], "no-flang-libs">, Group<flang_rt_Group>,
+  HelpText<"Do not link against Flang libraries">;
+def r8: Flag<["-"], "r8">, Group<pgi_fortran_Group>,
+  HelpText<"Treat REAL as REAL*8">;
+def i8: Flag<["-"], "i8">, Group<pgi_fortran_Group>,
+  HelpText<"Treat INTEGER and LOGICAL as INTEGER*8 and LOGICAL*8">;
+def no_fortran_main: Flag<["-"], "fno-fortran-main">, Group<gfortran_Group>,
+  HelpText<"Don't link in Fortran main">;
+def Mnomain: Flag<["-"], "Mnomain">, Group<pgi_fortran_Group>,
+  HelpText<"Don't link in Fortran main">;
+def frelaxed_math : Flag<["-"], "frelaxed-math">, Group<pgi_fortran_Group>,
+  HelpText<"Use relaxed Math intrinsic functions">;
+def Memit_dwarf_common_blocks_name: Flag<["-"], "Memit-dwarf-common-blocks-name">,
+  Group<pgi_fortran_Group>, HelpText<"Emit COMMON blocks name in DWARF">;
+def Munixlogical: Flag<["-"], "Munixlogical">, Group<pgi_fortran_Group>,
+  HelpText<"Use unixlogical for all loigical operations">;
+
+// Flang internal debug options
+def Mx_EQ : Joined<["-"], "Mx,">, Group<pgi_fortran_Group>;
+def My_EQ : Joined<["-"], "My,">, Group<pgi_fortran_Group>;
+def Hx_EQ : Joined<["-"], "Hx,">, Group<pgi_fortran_Group>;
+def Hy_EQ : Joined<["-"], "Hy,">, Group<pgi_fortran_Group>;
+def Wm_EQ : Joined<["-"], "Wm,">, Group<pgi_fortran_Group>;
+
+def Mq_EQ : Joined<["-"], "Mq,">, Group<pgi_fortran_Group>;
+def Hq_EQ : Joined<["-"], "Hq,">, Group<pgi_fortran_Group>;
+def Mqq_EQ : Joined<["-"], "Mqq,">, Group<pgi_fortran_Group>;
+def Hqq_EQ : Joined<["-"], "Hqq,">, Group<pgi_fortran_Group>;
+def Wh_EQ : Joined<["-"], "Wh,">, Group<pgi_fortran_Group>;
+#endif
 def hlsl_entrypoint : Option<["-"], "hlsl-entry", KIND_SEPARATE>,
                       Group<dxc_Group>,
                       Flags<[CC1Option]>,
diff --git a/clang/include/clang/Driver/ToolChain.h b/clang/include/clang/Driver/ToolChain.h
index 2e74507f7126..735e72491488 100644
--- a/clang/include/clang/Driver/ToolChain.h
+++ b/clang/include/clang/Driver/ToolChain.h
@@ -651,6 +651,16 @@ public:
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const;
 
+#ifdef ENABLE_CLASSIC_FLANG
+  /// \brief Add the flang arguments for system include paths.
+  ///
+  /// This routine is responsible for adding the -stdinc argument to
+  /// include headers and module files from standard system header directories.
+  virtual void
+  AddFlangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
+                            llvm::opt::ArgStringList &Flang1Args) const { }
+#endif
+
   /// Add options that need to be passed to cc1 for this target.
   virtual void addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                                      llvm::opt::ArgStringList &CC1Args,
@@ -757,6 +767,13 @@ public:
   virtual void AddHIPRuntimeLibArgs(const llvm::opt::ArgList &Args,
                                     llvm::opt::ArgStringList &CmdArgs) const {}
 
+#ifdef ENABLE_CLASSIC_FLANG
+  /// AddFortranStdlibLibArgs - Add the system specific linker arguments to use
+  /// for the given Fortran runtime library type.
+  virtual void AddFortranStdlibLibArgs(const llvm::opt::ArgList &Args,
+                                       llvm::opt::ArgStringList &CmdArgs) const;
+#endif
+
   /// Return sanitizers which are available in this toolchain.
   virtual SanitizerMask getSupportedSanitizers() const;
 
diff --git a/clang/include/clang/Driver/Types.def b/clang/include/clang/Driver/Types.def
index aaea3ec0f9c8..2f241b02676b 100644
--- a/clang/include/clang/Driver/Types.def
+++ b/clang/include/clang/Driver/Types.def
@@ -77,8 +77,15 @@ TYPE("c++-module-cpp-output",    PP_CXXModule, INVALID,         "iim",    phases
 TYPE("ada",                      Ada,          INVALID,         nullptr,  phases::Compile, phases::Backend, phases::Assemble, phases::Link)
 TYPE("assembler",                PP_Asm,       INVALID,         "s",      phases::Assemble, phases::Link)
 TYPE("assembler-with-cpp",       Asm,          PP_Asm,          "S",      phases::Preprocess, phases::Assemble, phases::Link)
+#ifdef ENABLE_CLASSIC_FLANG
+TYPE("f77",                      PP_F_FixedForm, INVALID,       "f",      phases::Compile, phases::Backend, phases::Assemble, phases::Link)
+TYPE("f77-cpp-input",            F_FixedForm,  PP_F_FixedForm,  "F",      phases::Preprocess, phases::Compile, phases::Backend, phases::Assemble, phases::Link)
+TYPE("f95",                      PP_F_FreeForm, INVALID,        "f95",    phases::Compile, phases::Backend, phases::Assemble, phases::Link)
+TYPE("f95-cpp-input",            F_FreeForm,   PP_F_FreeForm,   "F95",    phases::Preprocess, phases::Compile, phases::Backend, phases::Assemble, phases::Link)
+#else
 TYPE("f95",                      PP_Fortran,   INVALID,         "i",      phases::Compile, phases::Backend, phases::Assemble, phases::Link)
 TYPE("f95-cpp-input",            Fortran,      PP_Fortran,      nullptr,  phases::Preprocess, phases::Compile, phases::Backend, phases::Assemble, phases::Link)
+#endif
 TYPE("java",                     Java,         INVALID,         nullptr,  phases::Compile, phases::Backend, phases::Assemble, phases::Link)
 
 // LLVM IR/LTO types. We define separate types for IR and LTO because LTO
diff --git a/clang/include/clang/Driver/Types.h b/clang/include/clang/Driver/Types.h
index 4a21af3534de..3a8b785a4c39 100644
--- a/clang/include/clang/Driver/Types.h
+++ b/clang/include/clang/Driver/Types.h
@@ -95,6 +95,14 @@ namespace types {
   /// isOpenCL - Is this an "OpenCL" input.
   bool isOpenCL(ID Id);
 
+#ifdef ENABLE_CLASSIC_FLANG
+  /// isFreeFormFortran -- is it a free form layout Fortran input
+  bool isFreeFormFortran(ID Id);
+
+  /// isFixedFormFortran -- is it a fixed form layout Fortran input
+  bool isFixedFormFortran(ID Id);
+#endif
+
   /// isHLSL - Is this an HLSL input.
   bool isHLSL(ID Id);
 
diff --git a/clang/include/clang/Frontend/Utils.h b/clang/include/clang/Frontend/Utils.h
index 143cf4359f00..c51c617c1379 100644
--- a/clang/include/clang/Frontend/Utils.h
+++ b/clang/include/clang/Frontend/Utils.h
@@ -17,8 +17,10 @@
 #include "clang/Basic/LLVM.h"
 #include "clang/Driver/OptionUtils.h"
 #include "clang/Frontend/DependencyOutputOptions.h"
+#include "clang/Basic/TargetInfo.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSet.h"
@@ -31,6 +33,12 @@
 #include <utility>
 #include <vector>
 
+namespace llvm {
+
+class StringRef;
+
+} // namespace llvm
+
 namespace clang {
 
 class ASTReader;
@@ -39,6 +47,7 @@ class CompilerInvocation;
 class DiagnosticsEngine;
 class ExternalSemaSource;
 class FrontendOptions;
+class MacroBuilder;
 class PCHContainerReader;
 class Preprocessor;
 class PreprocessorOptions;
@@ -54,6 +63,29 @@ void InitializePreprocessor(Preprocessor &PP, const PreprocessorOptions &PPOpts,
 void DoPrintPreprocessedInput(Preprocessor &PP, raw_ostream *OS,
                               const PreprocessorOutputOptions &Opts);
 
+/// DefineTypeSize - Emit a macro to the predefines buffer that declares a macro
+/// named MacroName with the max value for a type with width 'TypeWidth' a
+/// signedness of 'isSigned' and with a value suffix of 'ValSuffix' (e.g. LL).
+template<typename T>
+static void DefineTypeSize(const Twine &MacroName, unsigned TypeWidth,
+                           StringRef ValSuffix, bool isSigned,
+                           T &Builder) {
+  static_assert(std::is_base_of<MacroBuilder, T>::value, "Illegal T value");
+  llvm::APInt MaxVal = isSigned ? llvm::APInt::getSignedMaxValue(TypeWidth)
+                                : llvm::APInt::getMaxValue(TypeWidth);
+  Builder.defineMacro(MacroName, toString(MaxVal, 10, isSigned) + ValSuffix);
+}
+
+/// DefineTypeSize - An overloaded helper that uses TargetInfo to determine
+/// the width, suffix, and signedness of the given type
+template<typename T>
+static void DefineTypeSize(const Twine &MacroName, TargetInfo::IntType Ty,
+                           const TargetInfo &TI, T &Builder) {
+  static_assert(std::is_base_of<MacroBuilder, T>::value, "Illegal T value");
+  DefineTypeSize(MacroName, TI.getTypeWidth(Ty), TI.getTypeConstantSuffix(Ty),
+                 TI.isTypeSigned(Ty), Builder);
+}
+
 /// An interface for collecting the dependencies of a compilation. Users should
 /// use \c attachToPreprocessor and \c attachToASTReader to get all of the
 /// dependencies.
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index 483f3e787a78..f962d60870d1 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -272,6 +272,12 @@ static TargetLibraryInfoImpl *createTLII(llvm::Triple &TargetTriple,
     TLII->addVectorizableFunctionsFromVecLib(TargetLibraryInfoImpl::MASSV,
                                              TargetTriple);
     break;
+#ifdef ENABLE_CLASSIC_FLANG
+  case CodeGenOptions::PGMATH:
+    TLII->addVectorizableFunctionsFromVecLib(TargetLibraryInfoImpl::PGMATH,
+                                             TargetTriple);
+    break;
+#endif
   case CodeGenOptions::SVML:
     TLII->addVectorizableFunctionsFromVecLib(TargetLibraryInfoImpl::SVML,
                                              TargetTriple);
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index d8eb2aecb87a..3b140860cce4 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -3980,7 +3980,8 @@ CGDebugInfo::getGlobalVariableForwardDeclaration(const VarDecl *VD) {
   auto Align = getDeclAlignIfRequired(VD, CGM.getContext());
   auto *GV = DBuilder.createTempGlobalVariableFwdDecl(
       DContext, Name, LinkageName, Unit, Line, getOrCreateType(T, Unit),
-      !VD->isExternallyVisible(), nullptr, TemplateParameters, Align);
+      !VD->isExternallyVisible(), nullptr, TemplateParameters,
+      llvm::DINode::FlagZero, Align);
   FwdDeclReplaceMap.emplace_back(
       std::piecewise_construct,
       std::make_tuple(cast<VarDecl>(VD->getCanonicalDecl())),
@@ -5467,7 +5468,7 @@ void CGDebugInfo::EmitGlobalVariable(llvm::GlobalVariable *Var,
         Var->hasLocalLinkage(), true,
         Expr.empty() ? nullptr : DBuilder.createExpression(Expr),
         getOrCreateStaticDataMemberDeclarationOrNull(D), TemplateParameters,
-        Align, Annotations);
+        llvm::DINode::FlagZero, Align, Annotations);
     Var->addDebugInfo(GVE);
   }
   DeclCache[D->getCanonicalDecl()].reset(GVE);
@@ -5563,7 +5564,7 @@ void CGDebugInfo::EmitGlobalVariable(const ValueDecl *VD, const APValue &Init) {
   GV.reset(DBuilder.createGlobalVariableExpression(
       DContext, Name, StringRef(), Unit, getLineNumber(VD->getLocation()), Ty,
       true, true, InitExpr, getOrCreateStaticDataMemberDeclarationOrNull(VarD),
-      TemplateParameters, Align));
+      TemplateParameters, llvm::DINode::FlagZero, Align));
 }
 
 void CGDebugInfo::EmitExternalVariable(llvm::GlobalVariable *Var,
@@ -5581,7 +5582,8 @@ void CGDebugInfo::EmitExternalVariable(llvm::GlobalVariable *Var,
   llvm::DIGlobalVariableExpression *GVE =
       DBuilder.createGlobalVariableExpression(
           DContext, Name, StringRef(), Unit, getLineNumber(D->getLocation()),
-          Ty, false, false, nullptr, nullptr, nullptr, Align);
+          Ty, false, false, nullptr, nullptr, nullptr, llvm::DINode::FlagZero,
+          Align);
   Var->addDebugInfo(GVE);
 }
 
diff --git a/clang/lib/Driver/CMakeLists.txt b/clang/lib/Driver/CMakeLists.txt
index a6bd2d41e797..ac30007588b1 100644
--- a/clang/lib/Driver/CMakeLists.txt
+++ b/clang/lib/Driver/CMakeLists.txt
@@ -14,6 +14,12 @@ if(WIN32)
   set(system_libs version)
 endif()
 
+if(LLVM_ENABLE_CLASSIC_FLANG)
+  set(TOOLCHAINS_FLANG_CPP ToolChains/ClassicFlang.cpp)
+else()
+  set(TOOLCHAINS_FLANG_CPP ToolChains/Flang.cpp)
+endif()
+
 add_clang_library(clangDriver
   Action.cpp
   Compilation.cpp
@@ -56,7 +62,7 @@ add_clang_library(clangDriver
   ToolChains/Cuda.cpp
   ToolChains/Darwin.cpp
   ToolChains/DragonFly.cpp
-  ToolChains/Flang.cpp
+  ${TOOLCHAINS_FLANG_CPP}
   ToolChains/FreeBSD.cpp
   ToolChains/Fuchsia.cpp
   ToolChains/Gnu.cpp
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index a7e4edb3ab5a..8bfee5928fe5 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -377,10 +377,14 @@ phases::ID Driver::getFinalPhase(const DerivedArgList &DAL,
              (PhaseArg = DAL.getLastArg(options::OPT_fmodule_header,
                                         options::OPT_fmodule_header_EQ))) {
     FinalPhase = phases::Precompile;
+
     // -{fsyntax-only,-analyze,emit-ast} only run up to the compiler.
   } else if ((PhaseArg = DAL.getLastArg(options::OPT_fsyntax_only)) ||
              (PhaseArg = DAL.getLastArg(options::OPT_print_supported_cpus)) ||
              (PhaseArg = DAL.getLastArg(options::OPT_module_file_info)) ||
+#ifdef ENABLE_CLASSIC_FLANG
+             (PhaseArg = DAL.getLastArg(options::OPT_emit_flang_llvm)) ||
+#endif
              (PhaseArg = DAL.getLastArg(options::OPT_verify_pch)) ||
              (PhaseArg = DAL.getLastArg(options::OPT_rewrite_objc)) ||
              (PhaseArg = DAL.getLastArg(options::OPT_rewrite_legacy_objc)) ||
@@ -1983,7 +1987,11 @@ void Driver::PrintHelp(bool ShowHidden) const {
 
 void Driver::PrintVersion(const Compilation &C, raw_ostream &OS) const {
   if (IsFlangMode()) {
+#ifdef ENABLE_CLASSIC_FLANG
+    OS << getClangToolFullVersion("flang") << '\n';
+#else
     OS << getClangToolFullVersion("flang-new") << '\n';
+#endif
   } else {
     // FIXME: The following handlers should use a callback mechanism, we don't
     // know what the client would like to do.
@@ -2665,7 +2673,15 @@ void Driver::BuildInputs(const ToolChain &TC, DerivedArgList &Args,
         // stdin must be handled specially.
         if (memcmp(Value, "-", 2) == 0) {
           if (IsFlangMode()) {
+#ifdef ENABLE_CLASSIC_FLANG
+          // If running with -E, treat as needing preprocessing
+          if (!Args.hasArgNoClaim(options::OPT_E))
+            Ty = types::TY_PP_F_FreeForm;
+          else
+            Ty = types::TY_F_FreeForm;
+#else
             Ty = types::TY_Fortran;
+#endif
           } else {
             // If running with -E, treat as a C input (this changes the
             // builtin macros, for example). This may be overridden by -ObjC
@@ -2687,6 +2703,16 @@ void Driver::BuildInputs(const ToolChain &TC, DerivedArgList &Args,
           // idea of what .s is.
           if (const char *Ext = strrchr(Value, '.'))
             Ty = TC.LookupTypeForExtension(Ext + 1);
+#ifdef ENABLE_CLASSIC_FLANG
+            // If called with -E, treat the inputs as needing preprocessing
+            // regardless of extension
+            if (IsFlangMode() && Args.hasArgNoClaim(options::OPT_E)) {
+              if (Ty == types::TY_PP_F_FreeForm)
+                Ty = types::TY_F_FreeForm;
+              else if (Ty == types::TY_PP_F_FixedForm)
+                Ty = types::TY_F_FixedForm;
+            }
+#endif
 
           if (Ty == types::TY_INVALID) {
             if (IsCLMode() && (Args.hasArgNoClaim(options::OPT_E) || CCGenDiagnostics))
@@ -4011,6 +4037,14 @@ void Driver::handleArguments(Compilation &C, DerivedArgList &Args,
       if (InputArg->isClaimed())
         continue;
 
+#ifdef ENABLE_CLASSIC_FLANG
+      // If the input is detected as already preprocessed (e.g. has the .f95
+      // extension), and the user specifies -E, preprocess the file anyway.
+      if (IsFlangMode() && InitialPhase == phases::Compile &&
+          FinalPhase == phases::Preprocess)
+        continue;
+#endif
+
       // Claim here to avoid the more general unused warning.
       InputArg->claim();
 
@@ -4745,6 +4779,10 @@ Action *Driver::ConstructPhaseAction(
       return C.MakeAction<VerifyPCHJobAction>(Input, types::TY_Nothing);
     if (Args.hasArg(options::OPT_extract_api))
       return C.MakeAction<ExtractAPIJobAction>(Input, types::TY_API_INFO);
+#ifdef ENABLE_CLASSIC_FLANG
+    if (IsFlangMode())
+      return C.MakeAction<CompileJobAction>(Input, types::TY_LLVM_IR);
+#endif
     return C.MakeAction<CompileJobAction>(Input, types::TY_LLVM_BC);
   }
   case phases::Backend: {
@@ -5199,6 +5237,12 @@ class ToolSelector final {
     if (!T->hasIntegratedBackend() && !(OutputIsLLVM && T->canEmitIR()))
       return nullptr;
 
+#ifdef ENABLE_CLASSIC_FLANG
+    // Classic Flang is not integrated with the backend.
+    if (C.getDriver().IsFlangMode() && !T->hasIntegratedAssembler())
+      return nullptr;
+#endif
+
     if (T->canEmitIR() && ((SaveTemps && !InputIsBitcode) || EmbedBitcode))
       return nullptr;
 
@@ -5214,8 +5258,17 @@ class ToolSelector final {
   /// are appended to \a CollapsedOffloadAction.
   void combineWithPreprocessor(const Tool *T, ActionList &Inputs,
                                ActionList &CollapsedOffloadAction) {
+#ifdef ENABLE_CLASSIC_FLANG
+    // flang1 always combines preprocessing and compilation.
+    // Do not return early even when -save-temps is used.
+    if (!T || !T->hasIntegratedCPP() ||
+        (strcmp(T->getName(), "classic-flang") &&
+         !canCollapsePreprocessorAction()))
+      return;
+#else
     if (!T || !canCollapsePreprocessorAction() || !T->hasIntegratedCPP())
       return;
+#endif
 
     // Attempt to get a preprocessor action dependence.
     ActionList PreprocessJobOffloadActions;
@@ -6418,8 +6471,11 @@ bool Driver::ShouldUseFlangCompiler(const JobAction &JA) const {
     return false;
 
   // And say "no" if this is not a kind of action flang understands.
-  if (!isa<PreprocessJobAction>(JA) && !isa<CompileJobAction>(JA) &&
-      !isa<BackendJobAction>(JA))
+  if (!isa<PreprocessJobAction>(JA) && !isa<CompileJobAction>(JA)
+#ifndef ENABLE_CLASSIC_FLANG
+      && !isa<BackendJobAction>(JA)
+#endif
+     )
     return false;
 
   return true;
diff --git a/clang/lib/Driver/OffloadBundler.cpp b/clang/lib/Driver/OffloadBundler.cpp
index 0ddfb07fdad5..acc4e9128cb1 100644
--- a/clang/lib/Driver/OffloadBundler.cpp
+++ b/clang/lib/Driver/OffloadBundler.cpp
@@ -864,6 +864,10 @@ CreateFileHandler(MemoryBuffer &FirstInput,
     return std::make_unique<TextFileHandler>(/*Comment=*/"#");
   if (FilesType == "ll")
     return std::make_unique<TextFileHandler>(/*Comment=*/";");
+#ifdef ENABLE_CLASSIC_FLANG
+  if (FilesType == "f95")
+    return std::make_unique<TextFileHandler>(/*Comment=*/"!");
+#endif
   if (FilesType == "bc")
     return std::make_unique<BinaryFileHandler>(BundlerConfig);
   if (FilesType == "s")
diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index 0146d8af3549..3d92b7c2a3bd 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -10,6 +10,9 @@
 #include "ToolChains/Arch/AArch64.h"
 #include "ToolChains/Arch/ARM.h"
 #include "ToolChains/Clang.h"
+#ifdef ENABLE_CLASSIC_FLANG
+#include "ToolChains/ClassicFlang.h"
+#endif
 #include "ToolChains/CommonArgs.h"
 #include "ToolChains/Flang.h"
 #include "ToolChains/InterfaceStubs.h"
@@ -441,7 +444,11 @@ Tool *ToolChain::getClang() const {
 
 Tool *ToolChain::getFlang() const {
   if (!Flang)
+#ifdef ENABLE_CLASSIC_FLANG
+    Flang.reset(new tools::ClassicFlang(*this));
+#else
     Flang.reset(new tools::Flang(*this));
+#endif
   return Flang.get();
 }
 
@@ -864,13 +871,13 @@ std::string ToolChain::GetStaticLibToolPath() const {
 
 types::ID ToolChain::LookupTypeForExtension(StringRef Ext) const {
   types::ID id = types::lookupTypeForExtension(Ext);
-
+#ifndef ENABLE_CLASSIC_FLANG
   // Flang always runs the preprocessor and has no notion of "preprocessed
   // fortran". Here, TY_PP_Fortran is coerced to TY_Fortran to avoid treating
   // them differently.
   if (D.IsFlangMode() && id == types::TY_PP_Fortran)
     id = types::TY_Fortran;
-
+#endif
   return id;
 }
 
@@ -1223,6 +1230,31 @@ void ToolChain::AddCCKextLibArgs(const ArgList &Args,
   CmdArgs.push_back("-lcc_kext");
 }
 
+#ifdef ENABLE_CLASSIC_FLANG
+void ToolChain::AddFortranStdlibLibArgs(const ArgList &Args,
+                                        ArgStringList &CmdArgs) const {
+  bool StaticFlangLibs = false;
+  if (Args.hasArg(options::OPT_staticFlangLibs)) {
+    StaticFlangLibs = true;
+    Args.ClaimAllArgs(options::OPT_staticFlangLibs);
+  }
+
+  if (StaticFlangLibs && !Args.hasArg(options::OPT_static))
+    CmdArgs.push_back("-Bstatic");
+  CmdArgs.push_back("-lflang");
+  CmdArgs.push_back("-lflangrti");
+  CmdArgs.push_back("-lpgmath");
+  if (StaticFlangLibs && !Args.hasArg(options::OPT_static))
+    CmdArgs.push_back("-Bdynamic");
+
+  // Always link Fortran executables with pthreads.
+  CmdArgs.push_back("-lpthread");
+
+  if (!Triple.isOSDarwin())
+    CmdArgs.push_back("-lrt");
+}
+#endif
+
 bool ToolChain::isFastMathRuntimeAvailable(const ArgList &Args,
                                            std::string &Path) const {
   // Do not check for -fno-fast-math or -fno-unsafe-math when -Ofast passed
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 793af55a1e5f..c5ba8a690687 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5367,6 +5367,66 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     }
     A->render(Args, CmdArgs);
   }
+#ifdef ENABLE_CLASSIC_FLANG
+  // Use PGMATH for Classic Flang by default.
+  else {
+    CmdArgs.push_back("-fveclib=PGMATH");
+  }
+
+  std::string PassRemarkVal(""), PassRemarkOpt("");
+  if (Args.getLastArg(options::OPT_Minfoall)) {
+    PassRemarkVal = ".*";
+    Args.ClaimAllArgs(options::OPT_Minfoall);
+  } else if (Arg *A = Args.getLastArg(options::OPT_Minfo_EQ)) {
+    for (StringRef val : A->getValues()) {
+      if (val.equals("all")) {
+        PassRemarkVal = ".*";
+        break;
+      } else if (val.equals("inline") || val.equals("vect")) {
+        PassRemarkVal += PassRemarkVal.empty() ? "" : "|";
+        PassRemarkVal += val;
+      } else {
+        D.Diag(diag::err_drv_clang_unsupported_minfo_arg)
+          << A->getOption().getName()
+          << val.str();
+        break;
+      }
+    }
+  }
+  PassRemarkOpt = "-pass-remarks=" + PassRemarkVal;
+  CmdArgs.push_back("-mllvm");
+  CmdArgs.push_back(Args.MakeArgString(PassRemarkOpt));
+  Args.ClaimAllArgs(options::OPT_Minfo_EQ);
+  PassRemarkVal.clear();
+  PassRemarkOpt.clear();
+
+  if (Args.getLastArg(options::OPT_Mneginfoall)) {
+    PassRemarkVal = ".*";
+    Args.ClaimAllArgs(options::OPT_Mneginfoall);
+  } else if (Arg *A = Args.getLastArg(options::OPT_Mneginfo_EQ)) {
+    for (StringRef val : A->getValues()) {
+      if (val.equals("all")) {
+        PassRemarkVal = ".*";
+        break;
+      } else if (val.equals("inline") || val.equals("vect")) {
+        PassRemarkVal += PassRemarkVal.empty() ? "" : "|";
+        PassRemarkVal += val;
+      } else {
+        D.Diag(diag::err_drv_clang_unsupported_minfo_arg)
+          << A->getOption().getName()
+          << val.str();
+        break;
+      }
+    }
+  }
+  PassRemarkOpt = "-pass-remarks-missed=" + PassRemarkVal;
+  CmdArgs.push_back("-mllvm");
+  CmdArgs.push_back(Args.MakeArgString(PassRemarkOpt));
+  PassRemarkOpt = "-pass-remarks-analysis=" + PassRemarkVal;
+  CmdArgs.push_back("-mllvm");
+  CmdArgs.push_back(Args.MakeArgString(PassRemarkOpt));
+  Args.ClaimAllArgs(options::OPT_Mneginfo_EQ);
+#endif
 
   if (Args.hasFlag(options::OPT_fmerge_all_constants,
                    options::OPT_fno_merge_all_constants, false))
diff --git a/clang/lib/Driver/ToolChains/ClassicFlang.cpp b/clang/lib/Driver/ToolChains/ClassicFlang.cpp
new file mode 100644
index 000000000000..b8be0be20b07
--- /dev/null
+++ b/clang/lib/Driver/ToolChains/ClassicFlang.cpp
@@ -0,0 +1,1217 @@
+//===-- ClassicFlang.cpp - Flang+LLVM ToolChain Implementations -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ClassicFlang.h"
+#include "CommonArgs.h"
+#include "clang/Driver/InputInfo.h"
+#include "clang/Basic/CharInfo.h"
+#include "clang/Basic/LangOptions.h"
+#include "clang/Basic/MacroBuilder.h"
+#include "clang/Basic/ObjCRuntime.h"
+#include "clang/Basic/TargetInfo.h"
+#include "clang/Basic/TargetOptions.h"
+#include "clang/Basic/Version.h"
+#include "clang/Config/config.h"
+#include "clang/Driver/DriverDiagnostic.h"
+#include "clang/Driver/Options.h"
+#include "clang/Driver/SanitizerArgs.h"
+#include "clang/Driver/XRayArgs.h"
+#include "clang/Frontend/CompilerInstance.h"
+#include "clang/Frontend/Utils.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/Option/ArgList.h"
+#include "llvm/Support/CodeGen.h"
+#include "llvm/Support/Compression.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/Process.h"
+#include "llvm/Support/YAMLParser.h"
+#include "llvm/TargetParser/TargetParser.h"
+
+#ifdef LLVM_ON_UNIX
+#include <unistd.h> // For getuid().
+#endif
+
+using namespace clang::driver;
+using namespace clang::driver::tools;
+using namespace clang;
+using namespace llvm::opt;
+
+class ClassicFlangMacroBuilder : public MacroBuilder {
+  ArgStringList &CmdArgs;
+  const ArgList &DriverArgs;
+  public:
+    ClassicFlangMacroBuilder(ArgStringList &UpperCmdArgs, const ArgList &DriverArgs, llvm::raw_string_ostream &Output)
+      : MacroBuilder(Output), CmdArgs(UpperCmdArgs), DriverArgs(DriverArgs) {
+    }
+    virtual void defineMacro(const Twine &Name, const Twine &Value = "1") override {
+      CmdArgs.push_back("-def");
+      CmdArgs.push_back(DriverArgs.MakeArgString(Name + Twine('=') + Value));
+    }
+};
+
+void ClassicFlang::ConstructJob(Compilation &C, const JobAction &JA,
+                         const InputInfo &Output, const InputInfoList &Inputs,
+                         const ArgList &Args, const char *LinkingOutput) const {
+  const Driver &D = getToolChain().getDriver();
+  const llvm::Triple &Triple = getToolChain().getEffectiveTriple();
+  ArgStringList CommonCmdArgs;
+  ArgStringList UpperCmdArgs;
+  ArgStringList LowerCmdArgs;
+  SmallString<256> Stem;
+  std::string OutFile;
+  bool NeedIEEE = true;
+  bool NeedFastMath = false;
+  bool NeedRelaxedMath = false;
+  bool AssociativeMath = false;
+  bool SignedZeros = true;
+
+  // Check number of inputs for sanity. We need at least one input.
+  assert(Inputs.size() >= 1 && "Must have at least one input.");
+
+  /***** Process file arguments to both parts *****/
+  const InputInfo &Input = Inputs[0];
+  types::ID InputType = Input.getType();
+  // Check file type sanity
+  assert(types::isAcceptedByFlang(InputType) && "Can only accept Fortran");
+
+  if (Args.hasArg(options::OPT_fsyntax_only, options::OPT_E)) {
+    // For -fsyntax-only and -E produce temp files only
+    Stem = C.getDriver().GetTemporaryPath("", "");
+  } else {
+    OutFile = Output.getFilename();
+    Stem = llvm::sys::path::filename(OutFile);
+    llvm::sys::path::replace_extension(Stem, "");
+  }
+
+#ifdef ENABLE_CLASSIC_FLANG
+  if (Args.hasArg(options::OPT_emit_flang_llvm)) {
+    // -emit-flang-llvm only supports asm output so claim -S to prevent warning
+    Args.ClaimAllArgs(options::OPT_S);
+  }
+#endif
+
+  // Add input file name to the compilation line
+  UpperCmdArgs.push_back(Input.getBaseInput());
+
+  // Add temporary output for ILM
+  const char * ILMFile = Args.MakeArgString(Stem + ".ilm");
+  LowerCmdArgs.push_back(ILMFile);
+  C.addTempFile(ILMFile);
+
+  // Generate -cmdline
+  std::string CmdLine("'+flang");
+  // ignore the first argument which reads "--driver-mode=fortran"
+  for (unsigned i = 1; i < Args.getNumInputArgStrings(); ++i) {
+    CmdLine.append(" ");
+    CmdLine.append(Args.getArgString(i));
+  }
+  CmdLine.append("'");
+
+  CommonCmdArgs.push_back("-cmdline");
+  CommonCmdArgs.push_back(Args.MakeArgString(CmdLine));
+
+  /***** Process common args *****/
+
+  // Add "inform level" flag
+  if (Args.hasArg(options::OPT_Minform_EQ)) {
+    // Parse arguments to set its value
+    for (Arg *A : Args.filtered(options::OPT_Minform_EQ)) {
+      A->claim();
+      CommonCmdArgs.push_back("-inform");
+      CommonCmdArgs.push_back(A->getValue(0));
+    }
+  } else {
+    // Default value
+    CommonCmdArgs.push_back("-inform");
+    CommonCmdArgs.push_back("warn");
+  }
+
+  for (auto Arg : Args.filtered(options::OPT_Msave_on)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-save");
+  }
+
+  for (auto Arg : Args.filtered(options::OPT_Msave_off)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-nosave");
+  }
+
+  // Treat denormalized numbers as zero: On
+  for (auto Arg : Args.filtered(options::OPT_Mdaz_on)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-x");
+    CommonCmdArgs.push_back("129");
+    CommonCmdArgs.push_back("4");
+    CommonCmdArgs.push_back("-y");
+    CommonCmdArgs.push_back("129");
+    CommonCmdArgs.push_back("0x400");
+  }
+
+  // Treat denormalized numbers as zero: Off
+  for (auto Arg : Args.filtered(options::OPT_Mdaz_off)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-y");
+    CommonCmdArgs.push_back("129");
+    CommonCmdArgs.push_back("4");
+    CommonCmdArgs.push_back("-x");
+    CommonCmdArgs.push_back("129");
+    CommonCmdArgs.push_back("0x400");
+  }
+
+  // Store constants in writable data segment
+  for (auto Arg : Args.filtered(options::OPT_Mwritable_constants)) {
+    Arg->claim();
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("183");
+    LowerCmdArgs.push_back("0x20000000");
+  }
+
+  // Bounds checking: On
+  for (auto Arg : Args.filtered(options::OPT_Mbounds_on)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-x");
+    CommonCmdArgs.push_back("70");
+    CommonCmdArgs.push_back("2");
+  }
+
+  // Bounds checking: Off
+  for (auto Arg : Args.filtered(options::OPT_Mbounds_off)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-y");
+    CommonCmdArgs.push_back("70");
+    CommonCmdArgs.push_back("2");
+  }
+
+  // Generate code allowing recursive subprograms
+  for (auto Arg : Args.filtered(options::OPT_Mrecursive_on)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-recursive");
+  }
+
+  // Disable recursive subprograms
+  for (auto Arg : Args.filtered(options::OPT_Mrecursive_off)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-norecursive");
+  }
+
+  // Enable generating reentrant code (disable optimizations that inhibit it)
+  for (auto Arg : Args.filtered(options::OPT_Mreentrant_on)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-reentrant");
+  }
+
+  // Allow optimizations inhibiting reentrancy
+  for (auto Arg : Args.filtered(options::OPT_Mreentrant_off)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-noreentrant");
+  }
+
+  // Swap byte order for unformatted IO
+  for (auto Arg : Args.filtered(options::OPT_Mbyteswapio, options::OPT_byteswapio)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-x");
+    CommonCmdArgs.push_back("125");
+    CommonCmdArgs.push_back("2");
+  }
+
+  // Contiguous pointer checks
+  if (Arg *A = Args.getLastArg(options::OPT_fsanitize_EQ)) {
+    for (StringRef val : A->getValues()) {
+      if (val.equals("discontiguous") || val.equals("undefined") ) {
+        // -x 54 0x40 -x 54 0x80 -x 54 0x200
+        UpperCmdArgs.push_back("-x");
+        UpperCmdArgs.push_back("54");
+        UpperCmdArgs.push_back("0x2c0");
+
+        // -fsanitze=discontiguous has no meaning in LLVM, only flang driver needs to
+        // recognize it. However -fsanitize=undefined needs to be passed on for further
+        // processing by the non-flang part of the driver.
+        if (val.equals("discontiguous"))
+          A->claim();
+        break;
+      }
+    }
+  }
+
+  // Treat backslashes as regular characters
+  for (auto Arg : Args.filtered(options::OPT_fno_backslash, options::OPT_Mbackslash)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-x");
+    CommonCmdArgs.push_back("124");
+    CommonCmdArgs.push_back("0x40");
+  }
+
+  // Treat backslashes as C-style escape characters
+  for (auto Arg : Args.filtered(options::OPT_fbackslash, options::OPT_Mnobackslash)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-y");
+    CommonCmdArgs.push_back("124");
+    CommonCmdArgs.push_back("0x40");
+  }
+
+  // handle OpemMP options
+  if (auto *A = Args.getLastArg(options::OPT_mp, options::OPT_nomp,
+                             options::OPT_fopenmp, options::OPT_fno_openmp)) {
+    for (auto Arg : Args.filtered(options::OPT_mp, options::OPT_nomp)) {
+      Arg->claim();
+    }
+    for (auto Arg : Args.filtered(options::OPT_fopenmp,
+                                  options::OPT_fno_openmp)) {
+      Arg->claim();
+    }
+
+    if (A->getOption().matches(options::OPT_mp) ||
+        A->getOption().matches(options::OPT_fopenmp)) {
+
+      CommonCmdArgs.push_back("-mp");
+
+       // Allocate threadprivate data local to the thread
+      CommonCmdArgs.push_back("-x");
+      CommonCmdArgs.push_back("69");
+      CommonCmdArgs.push_back("0x200");
+
+      // Use the 'fair' schedule as the default static schedule
+      // for parallel do loops
+      CommonCmdArgs.push_back("-x");
+      CommonCmdArgs.push_back("69");
+      CommonCmdArgs.push_back("0x400");
+
+      // Disable use of native atomic instructions
+      // for OpenMP atomics pending either a named
+      // option or a libatomic bundled with flang.
+      UpperCmdArgs.push_back("-x");
+      UpperCmdArgs.push_back("69");
+      UpperCmdArgs.push_back("0x1000");
+    }
+  }
+
+  // Align large objects on cache lines
+  for (auto Arg : Args.filtered(options::OPT_Mcache_align_on)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-x");
+    CommonCmdArgs.push_back("119");
+    CommonCmdArgs.push_back("0x10000000");
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("129");
+    LowerCmdArgs.push_back("0x40000000");
+  }
+
+  // Disable special alignment of large objects
+  for (auto Arg : Args.filtered(options::OPT_Mcache_align_off)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-y");
+    CommonCmdArgs.push_back("119");
+    CommonCmdArgs.push_back("0x10000000");
+    LowerCmdArgs.push_back("-y");
+    LowerCmdArgs.push_back("129");
+    LowerCmdArgs.push_back("0x40000000");
+  }
+
+  // -Mstack_arrays
+  for (auto Arg : Args.filtered(options::OPT_Mstackarrays)) {
+    Arg->claim();
+    CommonCmdArgs.push_back("-x");
+    CommonCmdArgs.push_back("54");
+    CommonCmdArgs.push_back("8");
+  }
+
+  // -Memit-dwarf-common-blocks-name, only add xbit to flang2.
+  for (auto Arg : Args.filtered(options::OPT_Memit_dwarf_common_blocks_name)) {
+    Arg->claim();
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("183");
+    LowerCmdArgs.push_back("0x40000000");
+  }
+
+  // -Munixlogical, only add xbit to flang2.
+  for (auto Arg : Args.filtered(options::OPT_Munixlogical)) {
+    Arg->claim();
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("125");
+    LowerCmdArgs.push_back("0x8");
+  }
+
+  // Last argument of -g/-gdwarfX should be taken.
+  Arg *GArg = Args.getLastArg(options::OPT_g_Flag);
+  Arg *GDwarfArg = Args.getLastArg(options::OPT_gdwarf_2,
+                                   options::OPT_gdwarf_3,
+                                   options::OPT_gdwarf_4,
+                                   options::OPT_gdwarf_5);
+
+  if (GArg || GDwarfArg) {
+
+    for (auto Arg : Args.filtered(options::OPT_g_Flag, options::OPT_gdwarf_2,
+                                  options::OPT_gdwarf_3, options::OPT_gdwarf_4,
+                                  options::OPT_gdwarf_5)) {
+      Arg->claim();
+    }
+
+    CommonCmdArgs.push_back("-x");
+    CommonCmdArgs.push_back("120");
+
+    if (!GDwarfArg) // -g without -gdwarf-X produces default (DWARFv4)
+      CommonCmdArgs.push_back("0x1000000");
+    else if (GDwarfArg->getOption().matches(options::OPT_gdwarf_2)) // -gdwarf-2
+      CommonCmdArgs.push_back("0x200");
+    else if (GDwarfArg->getOption().matches(options::OPT_gdwarf_3)) // -gdwarf-3
+      CommonCmdArgs.push_back("0x4000");
+    else if (GDwarfArg->getOption().matches(options::OPT_gdwarf_4)) // -gdwarf-4
+      CommonCmdArgs.push_back("0x1000000");
+    else if (GDwarfArg->getOption().matches(options::OPT_gdwarf_5)) // -gdwarf-5
+      CommonCmdArgs.push_back("0x2000000");
+    // Handle `-gpubnames` option separately.
+    for (auto Arg : Args.filtered(options::OPT_gpubnames)) {
+      Arg->claim();
+      CommonCmdArgs.push_back("-x");
+      CommonCmdArgs.push_back("120");
+      CommonCmdArgs.push_back("0x40000000"); // -gpubnames
+    }
+  }
+
+  // -Mipa has no effect
+  if (Arg *A = Args.getLastArg(options::OPT_Mipa)) {
+    D.Diag(diag::warn_drv_clang_unsupported)
+      << A->getAsString(Args);
+  }
+
+  // -Minline has no effect
+  if (Arg *A = Args.getLastArg(options::OPT_Minline_on)) {
+    D.Diag(diag::warn_drv_clang_unsupported)
+      << A->getAsString(Args);
+  }
+
+  // Handle -fdefault-real-8 (and its alias, -r8) and -fno-default-real-8
+  if (Arg *A = Args.getLastArg(options::OPT_r8,
+                               options::OPT_fdefault_real_8,
+                               options::OPT_fno_default_real_8)) {
+    const char * fl;
+    // For -f version add -x flag, for -fno add -y
+    if (A->getOption().matches(options::OPT_fno_default_real_8)) {
+      fl = "-y";
+    } else {
+      fl = "-x";
+    }
+
+    for (Arg *A : Args.filtered(options::OPT_r8,
+                                options::OPT_fdefault_real_8,
+                                options::OPT_fno_default_real_8)) {
+      A->claim();
+    }
+
+    UpperCmdArgs.push_back(fl);
+    UpperCmdArgs.push_back("124");
+    UpperCmdArgs.push_back("0x8");
+    UpperCmdArgs.push_back(fl);
+    UpperCmdArgs.push_back("124");
+    UpperCmdArgs.push_back("0x80000");
+  }
+
+  // Process and claim -i8/-fdefault-integer-8/-fno-default-integer-8 argument
+  if (Arg *A = Args.getLastArg(options::OPT_i8,
+                               options::OPT_fdefault_integer_8,
+                               options::OPT_fno_default_integer_8)) {
+    const char * fl;
+
+    if (A->getOption().matches(options::OPT_fno_default_integer_8)) {
+      fl = "-y";
+    } else {
+      fl = "-x";
+    }
+
+    for (Arg *A : Args.filtered(options::OPT_i8,
+                                options::OPT_fdefault_integer_8,
+                                options::OPT_fno_default_integer_8)) {
+      A->claim();
+    }
+
+    UpperCmdArgs.push_back(fl);
+    UpperCmdArgs.push_back("124");
+    UpperCmdArgs.push_back("0x10");
+  }
+
+  // Pass an arbitrary flag for first part of Fortran frontend
+  for (Arg *A : Args.filtered(options::OPT_Wh_EQ)) {
+    A->claim();
+    StringRef Value = A->getValue();
+    SmallVector<StringRef, 8> PassArgs;
+    Value.split(PassArgs, StringRef(","));
+    for (StringRef PassArg : PassArgs) {
+      UpperCmdArgs.push_back(Args.MakeArgString(PassArg));
+    }
+  }
+
+  // Flush to zero mode
+  // Disabled by default, but can be enabled by a switch
+  if (Args.hasArg(options::OPT_Mflushz_on)) {
+    // For -Mflushz set -x 129 2 for second part of Fortran frontend
+    for (Arg *A: Args.filtered(options::OPT_Mflushz_on)) {
+      A->claim();
+      LowerCmdArgs.push_back("-x");
+      LowerCmdArgs.push_back("129");
+      LowerCmdArgs.push_back("2");
+    }
+  } else {
+    LowerCmdArgs.push_back("-y");
+    LowerCmdArgs.push_back("129");
+    LowerCmdArgs.push_back("2");
+    for (Arg *A: Args.filtered(options::OPT_Mflushz_off)) {
+      A->claim();
+    }
+  }
+
+  // For -fPIC set -x 62 8 for second part of Fortran frontend
+  for (Arg *A: Args.filtered(options::OPT_fPIC)) {
+    A->claim();
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("62");
+    LowerCmdArgs.push_back("8");
+  }
+
+  StringRef OptOStr("0");
+  if (Arg *A = Args.getLastArg(options::OPT_O_Group)) {
+    if (A->getOption().matches(options::OPT_O4)) {
+      OptOStr = "4"; // FIXME what should this be?
+    } else if (A->getOption().matches(options::OPT_Ofast)) {
+      OptOStr = "2"; // FIXME what should this be?
+    } else if (A->getOption().matches(options::OPT_O0)) {
+      // intentionally do nothing
+    } else {
+      assert(A->getOption().matches(options::OPT_O) && "Must have a -O flag");
+      StringRef S(A->getValue());
+      if ((S == "s") || (S == "z")) {
+	// -Os = size; -Oz = more size
+	OptOStr = "2"; // FIXME -Os|-Oz => -opt ?
+      } else if ((S == "1") || (S == "2") || (S == "3")) {
+	OptOStr = S;
+      } else {
+	OptOStr = "4";
+      }
+    }
+  }
+  unsigned OptLevel = std::stoi(OptOStr.str());
+
+  if (Args.hasArg(options::OPT_g_Group)) {
+    // pass -g to lower and upper
+    CommonCmdArgs.push_back("-debug");
+  }
+
+  /* Pick the last among conflicting flags, if a positive and negative flag
+     exists for ex. "-ffast-math -fno-fast-math" they get nullified. Also any
+     previously overwritten flag remains that way.
+     For ex. "-Kieee -ffast-math -fno-fast-math". -Kieee gets overwritten by
+     -ffast-math which then gets negated by -fno-fast-math, finally behaving as
+     if none of those flags were passed.
+  */
+  for(Arg *A: Args.filtered(options::OPT_ffast_math, options::OPT_fno_fast_math,
+                        options::OPT_Ofast, options::OPT_Kieee_off,
+                        options::OPT_Kieee_on, options::OPT_frelaxed_math,
+                        options::OPT_fassociative_math,
+                        options::OPT_fno_associative_math,
+                        options::OPT_fsigned_zeros,
+                        options::OPT_fno_signed_zeros)) {
+    if (A->getOption().matches(options::OPT_ffast_math) ||
+        A->getOption().matches(options::OPT_Ofast)) {
+      NeedIEEE = NeedRelaxedMath = false;
+      NeedFastMath = true;
+    } else if (A->getOption().matches(options::OPT_Kieee_on)) {
+      NeedFastMath = NeedRelaxedMath = AssociativeMath = false;
+      NeedIEEE = SignedZeros = true;
+    } else if (A->getOption().matches(options::OPT_frelaxed_math)) {
+      NeedFastMath = NeedIEEE = false;
+      NeedRelaxedMath = true;
+    } else if (A->getOption().matches(options::OPT_fno_fast_math)) {
+      NeedFastMath = false;
+    } else if (A->getOption().matches(options::OPT_Kieee_off)) {
+      NeedIEEE = false;
+    } else if (A->getOption().matches(options::OPT_fassociative_math)) {
+      AssociativeMath = true;
+      NeedIEEE = SignedZeros = false;
+    } else if (A->getOption().matches(options::OPT_fno_associative_math)) {
+      AssociativeMath = false;
+    } else if (A->getOption().matches(options::OPT_fsigned_zeros)) {
+      SignedZeros = true;
+      AssociativeMath = false;
+    } else if (A->getOption().matches(options::OPT_fno_signed_zeros)) {
+      SignedZeros = NeedIEEE = false;
+    }
+    A->claim();
+  }
+
+  // fp-contract=fast is the default
+  bool EnableFPContraction = true;
+  if (Arg *A = Args.getLastArg(options::OPT_ffp_contract,
+                             options::OPT_Mfma_on,
+                             options::OPT_fma,
+                             options::OPT_Mfma_off,
+                             options::OPT_nofma)) {
+    auto Opt = A->getOption();
+    if (Opt.matches(options::OPT_ffp_contract)) {
+      StringRef Val = A->getValue();
+      if ((Val == "fast") || (Val == "on")) {
+        EnableFPContraction = true;
+      } else if (Val == "off") {
+        EnableFPContraction = false;
+      } else {
+        D.Diag(diag::err_drv_unsupported_option_argument)
+          << A->getOption().getName() << Val;
+      }
+    } else if(Opt.matches(options::OPT_Mfma_on) ||
+              Opt.matches(options::OPT_fma)) {
+      EnableFPContraction = true;
+    } else {
+      EnableFPContraction = false;
+    }
+  }
+
+  if(OptLevel == 0)
+    EnableFPContraction = false;
+
+  // Emit contract math instructions.
+  // Step 1 : Generate fma instructions in flang (can override with fma flag)
+  // Step 2 : Propagate fma contract information to LLVM to further
+  //          exploit contraction opportunities
+  if (EnableFPContraction) {
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("172");
+    LowerCmdArgs.push_back("0x40000000");
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("179");
+    LowerCmdArgs.push_back("1");
+    // Step 2
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("216");
+    LowerCmdArgs.push_back("0x1000");
+  } else {
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("171");
+    LowerCmdArgs.push_back("0x40000000");
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("178");
+    LowerCmdArgs.push_back("1");
+  }
+
+  if (NeedFastMath) {
+    // Lower: -x 216 1
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("216");
+    LowerCmdArgs.push_back("1");
+    // Common: -ieee 0
+    CommonCmdArgs.push_back("-ieee");
+    CommonCmdArgs.push_back("0");
+  } else if (NeedIEEE) {
+    // Common: -y 129 2
+    CommonCmdArgs.push_back("-y");
+    CommonCmdArgs.push_back("129");
+    CommonCmdArgs.push_back("2");
+    // Lower: -x 6 0x100
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("6");
+    LowerCmdArgs.push_back("0x100");
+    // Lower: -x 42 0x400000
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("42");
+    LowerCmdArgs.push_back("0x400000");
+    // Lower: -y 129 4
+    LowerCmdArgs.push_back("-y");
+    LowerCmdArgs.push_back("129");
+    LowerCmdArgs.push_back("4");
+    // Lower: -x 129 0x400
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("129");
+    LowerCmdArgs.push_back("0x400");
+    // Lower: -y 216 1 (OPT_fno_fast_math)
+    LowerCmdArgs.push_back("-y");
+    LowerCmdArgs.push_back("216");
+    LowerCmdArgs.push_back("1");
+    // Common: -ieee 1
+    CommonCmdArgs.push_back("-ieee");
+    CommonCmdArgs.push_back("1");
+  } else if (NeedRelaxedMath) {
+    // Lower: -x 15 0x400
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("15");
+    LowerCmdArgs.push_back("0x400");
+    // Lower: -y 216 1 (OPT_fno_fast_math)
+    LowerCmdArgs.push_back("-y");
+    LowerCmdArgs.push_back("216");
+    LowerCmdArgs.push_back("1");
+    // Common: -ieee 0
+    CommonCmdArgs.push_back("-ieee");
+    CommonCmdArgs.push_back("0");
+  } else {
+    // Common: -ieee 0
+    CommonCmdArgs.push_back("-ieee");
+    CommonCmdArgs.push_back("0");
+  }
+
+  /***** Upper part of the Fortran frontend *****/
+
+  // TODO do we need to invoke this under GDB sometimes?
+  const char *UpperExec = Args.MakeArgString(getToolChain().GetProgramPath("flang1"));
+
+  UpperCmdArgs.push_back("-opt"); UpperCmdArgs.push_back(Args.MakeArgString(OptOStr));
+  UpperCmdArgs.push_back("-terse"); UpperCmdArgs.push_back("1");
+  UpperCmdArgs.push_back("-inform"); UpperCmdArgs.push_back("warn");
+  UpperCmdArgs.push_back("-nohpf");
+  UpperCmdArgs.push_back("-nostatic");
+  UpperCmdArgs.append(CommonCmdArgs.begin(), CommonCmdArgs.end()); // Append common arguments
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("19"); UpperCmdArgs.push_back("0x400000");
+  UpperCmdArgs.push_back("-quad");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("68"); UpperCmdArgs.push_back("0x1");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("59"); UpperCmdArgs.push_back("4");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("15"); UpperCmdArgs.push_back("2");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("49"); UpperCmdArgs.push_back("0x400004");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("51"); UpperCmdArgs.push_back("0x20");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("57"); UpperCmdArgs.push_back("0x4c");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("58"); UpperCmdArgs.push_back("0x10000");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("124"); UpperCmdArgs.push_back("0x1000");
+  UpperCmdArgs.push_back("-tp"); UpperCmdArgs.push_back("px");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("57"); UpperCmdArgs.push_back("0xfb0000");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("58"); UpperCmdArgs.push_back("0x78031040");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("47"); UpperCmdArgs.push_back("0x08");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("48"); UpperCmdArgs.push_back("4608");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("49"); UpperCmdArgs.push_back("0x100");
+  if (OptLevel >= 2) {
+    UpperCmdArgs.push_back("-x");
+    UpperCmdArgs.push_back("70");
+    UpperCmdArgs.push_back("0x6c00");
+    UpperCmdArgs.push_back("-x");
+    UpperCmdArgs.push_back("119");
+    UpperCmdArgs.push_back("0x10000000");
+    UpperCmdArgs.push_back("-x");
+    UpperCmdArgs.push_back("129");
+    UpperCmdArgs.push_back("2");
+    UpperCmdArgs.push_back("-x");
+    UpperCmdArgs.push_back("47");
+    UpperCmdArgs.push_back("0x400000");
+    UpperCmdArgs.push_back("-x");
+    UpperCmdArgs.push_back("52");
+    UpperCmdArgs.push_back("2");
+  }
+
+  // Add system include arguments.
+  getToolChain().AddFlangSystemIncludeArgs(Args, UpperCmdArgs);
+
+  // Use clang's predefined macros
+  DiagnosticsEngine DE(new DiagnosticIDs(), new DiagnosticOptions, new IgnoringDiagConsumer());
+  std::shared_ptr<clang::TargetOptions> TO = std::make_shared<clang::TargetOptions>();
+  TO->Triple = Triple.getTriple();
+  std::shared_ptr<TargetInfo> TI(clang::TargetInfo::CreateTargetInfo(DE, TO));
+  std::string PredefineBuffer;
+  llvm::raw_string_ostream Predefines(PredefineBuffer);
+  ClassicFlangMacroBuilder Builder(UpperCmdArgs, Args, Predefines);
+
+  LangOptions LO;
+  VersionTuple VT = getToolChain().computeMSVCVersion(&D, Args);
+  if (!VT.empty()) {
+    // Set the MSCompatibility version. Subminor version has 5 decimal digits.
+    // Minor and major versions have 2 decimal digits each.
+    LO.MSCompatibilityVersion = VT.getMajor() * 10000000 +
+                                VT.getMinor().value_or(0) * 100000 +
+                                VT.getSubminor().value_or(0);
+  }
+
+  // Define Target specific macros like __linux__
+  TI->getTargetDefines(LO, Builder);
+
+  Builder.defineMacro("__SIZE_TYPE__",
+                      TargetInfo::getTypeName(TI->getSizeType()));
+  Builder.defineMacro(
+      "__PTRDIFF_TYPE__",
+      TargetInfo::getTypeName(TI->getPtrDiffType(LangAS::Default)));
+
+  if (TI->getPointerWidth(LangAS::Default) == 64 && TI->getLongWidth() == 64
+      && TI->getIntWidth() == 32) {
+    Builder.defineMacro("_LP64");
+    Builder.defineMacro("__LP64__");
+  }
+
+  if (TI->getPointerWidth(LangAS::Default) == 32 && TI->getLongWidth() == 32
+      && TI->getIntWidth() == 32) {
+    Builder.defineMacro("_ILP32");
+    Builder.defineMacro("__ILP32__");
+  }
+
+  DefineTypeSize("__LONG_MAX__", TargetInfo::SignedLong, *TI, Builder);
+
+  // Add additional predefined macros
+  switch (Triple.getArch()) {
+  case llvm::Triple::aarch64:
+    UpperCmdArgs.push_back("-def"); UpperCmdArgs.push_back("__ARM_ARCH__=8");
+    break;
+  case llvm::Triple::x86_64:
+    UpperCmdArgs.push_back("-def"); UpperCmdArgs.push_back("__amd_64__amd64__");
+    UpperCmdArgs.push_back("-def"); UpperCmdArgs.push_back("__k8");
+    UpperCmdArgs.push_back("-def"); UpperCmdArgs.push_back("__k8__");
+    break;
+  default: /* generic 64-bit */
+    ;
+  }
+  UpperCmdArgs.push_back("-def"); UpperCmdArgs.push_back("__THROW=");
+  UpperCmdArgs.push_back("-def"); UpperCmdArgs.push_back("__extension__=");
+  UpperCmdArgs.push_back("-def"); UpperCmdArgs.push_back("__PGLLVM__");
+
+  // Enable preprocessor
+  if (Args.hasArg(options::OPT_Mpreprocess) ||
+      Args.hasArg(options::OPT_cpp) ||
+      Args.hasArg(options::OPT_E) ||
+      types::getPreprocessedType(InputType) != types::TY_INVALID) {
+    UpperCmdArgs.push_back("-preprocess");
+    for (auto Arg : Args.filtered(options::OPT_Mpreprocess, options::OPT_cpp, options::OPT_E)) {
+      Arg->claim();
+    }
+
+    // When -E option is provided, run only the fortran preprocessor.
+    // Only in -E mode, consume -P if it exists
+    if (Args.hasArg(options::OPT_E)) {
+      UpperCmdArgs.push_back("-es");
+      // Line marker mode is disabled
+      if (Args.hasArg(options::OPT_P)) {
+        Args.ClaimAllArgs(options::OPT_P);
+      } else {
+        // -pp enables line marker mode in fortran preprocessor
+        UpperCmdArgs.push_back("-pp");
+      }
+    }
+  }
+
+  // Enable standards checking
+  if (Args.hasArg(options::OPT_Mstandard)) {
+    UpperCmdArgs.push_back("-standard");
+    for (auto Arg : Args.filtered(options::OPT_Mstandard)) {
+      Arg->claim();
+    }
+  }
+
+  // Free or fixed form file
+  if (Args.hasArg(options::OPT_fortran_format_Group)) {
+    // Override file name suffix, scan arguments for that
+    for (Arg *A : Args.filtered(options::OPT_fortran_format_Group)) {
+      A->claim();
+      switch (A->getOption().getID()) {
+        default:
+          llvm_unreachable("missed a case");
+         case options::OPT_ffixed_form:
+         case options::OPT_fno_free_form:
+         case options::OPT_Mfixed:
+         case options::OPT_Mfree_off:
+         case options::OPT_Mfreeform_off:
+           UpperCmdArgs.push_back("-nofreeform");
+           break;
+         case options::OPT_ffree_form:
+         case options::OPT_fno_fixed_form:
+         case options::OPT_Mfree_on:
+         case options::OPT_Mfreeform_on:
+           UpperCmdArgs.push_back("-freeform");
+           break;
+      }
+    }
+  } else {
+    // Deduce format from file name suffix
+    if (types::isFreeFormFortran(InputType)) {
+      UpperCmdArgs.push_back("-freeform");
+    } else {
+      UpperCmdArgs.push_back("-nofreeform");
+    }
+  }
+
+  // Extend lines to 132 characters
+  for (auto Arg : Args.filtered(options::OPT_Mextend)) {
+    Arg->claim();
+    UpperCmdArgs.push_back("-extend");
+  }
+
+  for (auto Arg : Args.filtered(options::OPT_ffixed_line_length_VALUE)) {
+    StringRef Value = Arg->getValue();
+    if (Value == "72") {
+      Arg->claim();
+    } else if (Value == "132") {
+      Arg->claim();
+      UpperCmdArgs.push_back("-extend");
+    } else {
+      D.Diag(diag::err_drv_unsupported_fixed_line_length)
+        << Arg->getAsString(Args);
+    }
+  }
+
+  // Add user-defined include directories
+  for (auto Arg : Args.filtered(options::OPT_I)) {
+    Arg->claim();
+    UpperCmdArgs.push_back("-idir");
+    UpperCmdArgs.push_back(Arg->getValue(0));
+  }
+
+  // Add user-defined module directories
+  for (auto Arg : Args.filtered(options::OPT_ModuleDir, options::OPT_J)) {
+    Arg->claim();
+    UpperCmdArgs.push_back("-moddir");
+    UpperCmdArgs.push_back(Arg->getValue(0));
+  }
+
+  // "Define" preprocessor flags
+  for (auto Arg : Args.filtered(options::OPT_D)) {
+    Arg->claim();
+    UpperCmdArgs.push_back("-def");
+    UpperCmdArgs.push_back(Arg->getValue(0));
+  }
+
+  // "Define" preprocessor flags
+  for (auto Arg : Args.filtered(options::OPT_U)) {
+    Arg->claim();
+    UpperCmdArgs.push_back("-undef");
+    UpperCmdArgs.push_back(Arg->getValue(0));
+  }
+
+  UpperCmdArgs.push_back("-vect"); UpperCmdArgs.push_back("48");
+
+  // Semantics for assignments to allocatables
+  if (Arg *A = Args.getLastArg(options::OPT_Mallocatable_EQ)) {
+    // Argument is passed explicitly
+    StringRef Value = A->getValue();
+    if (Value == "03") { // Enable Fortran 2003 semantics
+      UpperCmdArgs.push_back("-x"); // Set XBIT
+    } else if (Value == "95") { // Enable Fortran 2003 semantics
+      UpperCmdArgs.push_back("-y"); // Unset XBIT
+    } else {
+      D.Diag(diag::err_drv_invalid_allocatable_mode)
+        << A->getAsString(Args);
+    }
+  } else { // No argument passed
+    UpperCmdArgs.push_back("-x"); // Default is 03
+  }
+  UpperCmdArgs.push_back("54"); UpperCmdArgs.push_back("1"); // XBIT value
+
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("70"); UpperCmdArgs.push_back("0x40000000");
+  UpperCmdArgs.push_back("-y"); UpperCmdArgs.push_back("163"); UpperCmdArgs.push_back("0xc0000000");
+  UpperCmdArgs.push_back("-x"); UpperCmdArgs.push_back("189"); UpperCmdArgs.push_back("0x10");
+
+  // Enable NULL pointer checking
+  if (Args.hasArg(options::OPT_Mchkptr)) {
+    UpperCmdArgs.push_back("-x");
+    UpperCmdArgs.push_back("70");
+    UpperCmdArgs.push_back("4");
+    for (auto Arg : Args.filtered(options::OPT_Mchkptr)) {
+      Arg->claim();
+    }
+  }
+
+  // Set a -x flag for first part of Fortran frontend
+  for (Arg *A : Args.filtered(options::OPT_Hx_EQ)) {
+    A->claim();
+    StringRef Value = A->getValue();
+    auto XFlag = Value.split(",");
+    UpperCmdArgs.push_back("-x");
+    UpperCmdArgs.push_back(Args.MakeArgString(XFlag.first));
+    UpperCmdArgs.push_back(Args.MakeArgString(XFlag.second));
+  }
+
+  // Set a -y flag for first part of Fortran frontend
+  for (Arg *A : Args.filtered(options::OPT_Hy_EQ)) {
+    A->claim();
+    StringRef Value = A->getValue();
+    auto XFlag = Value.split(",");
+    UpperCmdArgs.push_back("-y");
+    UpperCmdArgs.push_back(Args.MakeArgString(XFlag.first));
+    UpperCmdArgs.push_back(Args.MakeArgString(XFlag.second));
+  }
+
+  // Set a -q (debug) flag for first part of Fortran frontend
+  for (Arg *A : Args.filtered(options::OPT_Hq_EQ)) {
+    A->claim();
+    StringRef Value = A->getValue();
+    auto XFlag = Value.split(",");
+    UpperCmdArgs.push_back("-q");
+    UpperCmdArgs.push_back(Args.MakeArgString(XFlag.first));
+    UpperCmdArgs.push_back(Args.MakeArgString(XFlag.second));
+  }
+
+  // Set a -qq (debug) flag for first part of Fortran frontend
+  for (Arg *A : Args.filtered(options::OPT_Hqq_EQ)) {
+    A->claim();
+    StringRef Value = A->getValue();
+    auto XFlag = Value.split(",");
+    UpperCmdArgs.push_back("-qq");
+    UpperCmdArgs.push_back(Args.MakeArgString(XFlag.first));
+    UpperCmdArgs.push_back(Args.MakeArgString(XFlag.second));
+  }
+
+  const char * STBFile = Args.MakeArgString(Stem + ".stb");
+  C.addTempFile(STBFile);
+  UpperCmdArgs.push_back("-stbfile");
+  UpperCmdArgs.push_back(STBFile);
+
+  const char * ModuleExportFile = Args.MakeArgString(Stem + ".cmod");
+  C.addTempFile(ModuleExportFile);
+  UpperCmdArgs.push_back("-modexport");
+  UpperCmdArgs.push_back(ModuleExportFile);
+
+  const char * ModuleIndexFile = Args.MakeArgString(Stem + ".cmdx");
+  C.addTempFile(ModuleIndexFile);
+  UpperCmdArgs.push_back("-modindex");
+  UpperCmdArgs.push_back(ModuleIndexFile);
+
+  UpperCmdArgs.push_back("-output");
+  UpperCmdArgs.push_back(ILMFile);
+
+  SmallString<256> Path;
+  if(Args.getAllArgValues(options::OPT_fopenmp_targets_EQ).size() > 0) {
+    SmallString<128> TargetInfo;
+    Path = llvm::sys::path::parent_path(Output.getFilename());
+    Arg* Tgts = Args.getLastArg(options::OPT_fopenmp_targets_EQ);
+    assert(Tgts && Tgts->getNumValues() &&
+           "OpenMP offloading has to have targets specified.");
+    for (unsigned i = 0; i < Tgts->getNumValues(); ++i) {
+      if (i)
+        TargetInfo += ',';
+      llvm::Triple T(Tgts->getValue(i));
+      TargetInfo += T.getTriple();
+    }
+    UpperCmdArgs.push_back("-fopenmp-targets");
+    UpperCmdArgs.push_back(Args.MakeArgString(TargetInfo.str()));
+  }
+
+  C.addCommand(std::make_unique<Command>(JA, *this, ResponseFileSupport::AtFileUTF8(), UpperExec, UpperCmdArgs, Inputs));
+
+  // For -fsyntax-only or -E that is it
+  if (Args.hasArg(options::OPT_fsyntax_only) ||
+      Args.hasArg(options::OPT_E)) return;
+
+  /***** Lower part of Fortran frontend *****/
+
+  const char *LowerExec = Args.MakeArgString(getToolChain().GetProgramPath("flang2"));
+
+  // TODO FLANG arg handling
+  LowerCmdArgs.push_back("-fn"); LowerCmdArgs.push_back(Input.getBaseInput());
+  LowerCmdArgs.push_back("-opt"); LowerCmdArgs.push_back(Args.MakeArgString(OptOStr));
+  LowerCmdArgs.push_back("-terse"); LowerCmdArgs.push_back("1");
+  LowerCmdArgs.push_back("-inform"); LowerCmdArgs.push_back("warn");
+  LowerCmdArgs.append(CommonCmdArgs.begin(), CommonCmdArgs.end()); // Append common arguments
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("68"); LowerCmdArgs.push_back("0x1");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("51"); LowerCmdArgs.push_back("0x20");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("119"); LowerCmdArgs.push_back("0xa10000");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("122"); LowerCmdArgs.push_back("0x40");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("123"); LowerCmdArgs.push_back("0x1000");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("127"); LowerCmdArgs.push_back("4");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("127"); LowerCmdArgs.push_back("17");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("19"); LowerCmdArgs.push_back("0x400000");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("28"); LowerCmdArgs.push_back("0x40000");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("120"); LowerCmdArgs.push_back("0x10000000");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("70"); LowerCmdArgs.push_back("0x8000");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("122"); LowerCmdArgs.push_back("1");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("125"); LowerCmdArgs.push_back("0x20000");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("164"); LowerCmdArgs.push_back("0x800000");
+  LowerCmdArgs.push_back("-quad");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("59"); LowerCmdArgs.push_back("4");
+  LowerCmdArgs.push_back("-tp"); LowerCmdArgs.push_back("px");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("120"); LowerCmdArgs.push_back("0x1000"); // debug lite
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("124"); LowerCmdArgs.push_back("0x1400");
+  LowerCmdArgs.push_back("-y"); LowerCmdArgs.push_back("15"); LowerCmdArgs.push_back("2");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("57"); LowerCmdArgs.push_back("0x3b0000");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("58"); LowerCmdArgs.push_back("0x48000000");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("49"); LowerCmdArgs.push_back("0x100");
+  LowerCmdArgs.push_back("-astype"); LowerCmdArgs.push_back("0");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("183"); LowerCmdArgs.push_back("4");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("121"); LowerCmdArgs.push_back("0x800");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("54"); LowerCmdArgs.push_back("0x10");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("70"); LowerCmdArgs.push_back("0x40000000");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("249"); LowerCmdArgs.push_back("170"); // LLVM version
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("124"); LowerCmdArgs.push_back("1");
+  LowerCmdArgs.push_back("-y"); LowerCmdArgs.push_back("163"); LowerCmdArgs.push_back("0xc0000000");
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("189"); LowerCmdArgs.push_back("0x10");
+  LowerCmdArgs.push_back("-y"); LowerCmdArgs.push_back("189"); LowerCmdArgs.push_back("0x4000000");
+
+  if (!SignedZeros) {
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("216");
+    LowerCmdArgs.push_back("0x8");
+  }
+  if (AssociativeMath) {
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back("216");
+    LowerCmdArgs.push_back("0x10");
+  }
+
+  // Remove "noinline" attriblute
+  LowerCmdArgs.push_back("-x"); LowerCmdArgs.push_back("183"); LowerCmdArgs.push_back("0x10");
+
+  // Add target features
+  std::vector<StringRef> Features;
+  std::string FeatureList = "";
+  getTargetFeatureList(D, Triple, Args, UpperCmdArgs, false, Features);
+  if (!Features.empty()) {
+    for (auto Feature : unifyTargetFeatures(Features)) {
+      if (!FeatureList.empty())
+        FeatureList += ',';
+      FeatureList += Feature;
+    }
+
+    LowerCmdArgs.push_back("-target_features");
+    LowerCmdArgs.push_back(Args.MakeArgString(FeatureList));
+  }
+
+  // Add vscale range
+  unsigned vscaleMin = 0;
+  unsigned vscaleMax = 0;
+  bool hasSVE = false;
+  if (Arg *A = Args.getLastArg(options::OPT_msve_vector_bits_EQ)) {
+    StringRef Val = A->getValue();
+    if (Val.equals("128") || Val.equals("256") || Val.equals("512") ||
+        Val.equals("1024") || Val.equals("2048") || Val.equals("128+") ||
+        Val.equals("256+") || Val.equals("512+") || Val.equals("1024+") ||
+        Val.equals("2048+")) {
+      unsigned Bits = 0;
+      if (Val.endswith("+"))
+        Val = Val.substr(0, Val.size() - 1);
+      else {
+        bool Invalid = Val.getAsInteger(10, Bits); (void)Invalid;
+        assert(!Invalid && "Failed to parse value");
+        vscaleMax = Bits / 128;
+      }
+ 
+      bool Invalid = Val.getAsInteger(10, Bits); (void)Invalid;
+      assert(!Invalid && "Failed to parse value");
+      vscaleMin = Bits / 128;
+    } else if (!Val.equals("scalable"))
+      getToolChain().getDriver().Diag(diag::warn_drv_clang_unsupported)
+          << A->getOption().getName() << Val;
+  }
+  for (auto Feature : unifyTargetFeatures(Features)) {
+    if (Feature.startswith("+sve")) {
+      hasSVE = true;
+      break;
+    }
+  }
+  if (vscaleMin || vscaleMax) {
+    LowerCmdArgs.push_back("-vscale_range_min");
+    LowerCmdArgs.push_back(Args.MakeArgString(
+        std::to_string(vscaleMin ? vscaleMin : 1)));
+    LowerCmdArgs.push_back("-vscale_range_max");
+    LowerCmdArgs.push_back(Args.MakeArgString(std::to_string(vscaleMax)));
+  } else {
+    if (hasSVE) {
+      LowerCmdArgs.push_back("-vscale_range_min");
+      LowerCmdArgs.push_back(Args.MakeArgString(std::to_string(1)));
+      LowerCmdArgs.push_back("-vscale_range_max");
+      LowerCmdArgs.push_back(Args.MakeArgString(std::to_string(16)));
+    }
+  }
+
+  // Set a -x flag for second part of Fortran frontend
+  for (Arg *A : Args.filtered(options::OPT_Mx_EQ)) {
+    A->claim();
+    StringRef Value = A->getValue();
+    auto XFlag = Value.split(",");
+    LowerCmdArgs.push_back("-x");
+    LowerCmdArgs.push_back(Args.MakeArgString(XFlag.first));
+    LowerCmdArgs.push_back(Args.MakeArgString(XFlag.second));
+  }
+
+  // Set a -y flag for second part of Fortran frontend
+  for (Arg *A : Args.filtered(options::OPT_My_EQ)) {
+    A->claim();
+    StringRef Value = A->getValue();
+    auto XFlag = Value.split(",");
+    LowerCmdArgs.push_back("-y");
+    LowerCmdArgs.push_back(Args.MakeArgString(XFlag.first));
+    LowerCmdArgs.push_back(Args.MakeArgString(XFlag.second));
+  }
+
+  // Set a -q (debug) flag for second part of Fortran frontend
+  for (Arg *A : Args.filtered(options::OPT_Mq_EQ)) {
+    A->claim();
+    StringRef Value = A->getValue();
+    auto XFlag = Value.split(",");
+    LowerCmdArgs.push_back("-q");
+    LowerCmdArgs.push_back(Args.MakeArgString(XFlag.first));
+    LowerCmdArgs.push_back(Args.MakeArgString(XFlag.second));
+  }
+
+  // Set a -qq (debug) flag for second part of Fortran frontend
+  for (Arg *A : Args.filtered(options::OPT_Mqq_EQ)) {
+    A->claim();
+    StringRef Value = A->getValue();
+    auto XFlag = Value.split(",");
+    LowerCmdArgs.push_back("-qq");
+    LowerCmdArgs.push_back(Args.MakeArgString(XFlag.first));
+    LowerCmdArgs.push_back(Args.MakeArgString(XFlag.second));
+  }
+
+  // Pass an arbitrary flag for second part of Fortran frontend
+  for (Arg *A : Args.filtered(options::OPT_Wm_EQ)) {
+    A->claim();
+    StringRef Value = A->getValue();
+    SmallVector<StringRef, 8> PassArgs;
+    Value.split(PassArgs, StringRef(","));
+    for (StringRef PassArg : PassArgs) {
+      LowerCmdArgs.push_back(Args.MakeArgString(PassArg));
+    }
+  }
+
+  LowerCmdArgs.push_back("-stbfile");
+  LowerCmdArgs.push_back(STBFile);
+
+  Path = llvm::sys::path::parent_path(Output.getFilename());
+  bool IsOpenMPDevice = JA.isDeviceOffloading(Action::OFK_OpenMP);
+
+  /* OpenMP GPU Offload */
+  if(Args.getAllArgValues(options::OPT_fopenmp_targets_EQ).size() > 0) {
+    SmallString<128> TargetInfo;//("-fopenmp-targets ");
+    SmallString<256> TargetInfoAsm;//("-fopenmp-targets-asm ");
+
+    Arg* Tgts = Args.getLastArg(options::OPT_fopenmp_targets_EQ);
+    assert(Tgts && Tgts->getNumValues() &&
+           "OpenMP offloading has to have targets specified.");
+    for (unsigned i = 0; i < Tgts->getNumValues(); ++i) {
+      if (i)
+        TargetInfo += ',';
+      // We need to get the string from the triple because it may be not exactly
+      // the same as the one we get directly from the arguments.
+      llvm::Triple T(Tgts->getValue(i));
+      TargetInfo += T.getTriple();
+      // We also need to give a output file
+      TargetInfoAsm += Path;
+      TargetInfoAsm += "/";
+      TargetInfoAsm += Stem;
+      TargetInfoAsm += "-";
+      TargetInfoAsm += T.getTriple();
+      TargetInfoAsm += ".ll";
+    }
+    // The driver is aware that flang2 can generate multiple files at the same time.
+    // We mimic it here by exchanging the output files.
+    // The driver always uses the output file of -asm.
+    LowerCmdArgs.push_back("-fopenmp-targets");
+    LowerCmdArgs.push_back(Args.MakeArgString(TargetInfo.str()));
+    if(IsOpenMPDevice) {
+      LowerCmdArgs.push_back("-fopenmp-targets-asm");
+      LowerCmdArgs.push_back(Args.MakeArgString(OutFile));
+      LowerCmdArgs.push_back("-asm");
+      LowerCmdArgs.push_back(Args.MakeArgString(TargetInfoAsm.str()));
+    } else {
+      LowerCmdArgs.push_back("-fopenmp-targets-asm");
+      LowerCmdArgs.push_back(Args.MakeArgString(TargetInfoAsm.str()));
+      LowerCmdArgs.push_back("-asm");
+      LowerCmdArgs.push_back(Args.MakeArgString(OutFile));
+    }
+  } else {
+    LowerCmdArgs.push_back("-asm");
+    LowerCmdArgs.push_back(Args.MakeArgString(OutFile));
+  }
+
+  bool IsWindowsMSVC = getToolChain().getTriple().isWindowsMSVCEnvironment();
+  if (IsWindowsMSVC && !Args.hasArg(options::OPT_noFlangLibs)) {
+    getToolChain().AddFortranStdlibLibArgs(Args, LowerCmdArgs);
+    for (auto Arg : Args.filtered(options::OPT_noFlangLibs)) {
+      Arg->claim();
+    }
+  }
+
+  C.addCommand(std::make_unique<Command>(JA, *this, ResponseFileSupport::AtFileUTF8(), LowerExec, LowerCmdArgs, Inputs));
+}
+
diff --git a/clang/lib/Driver/ToolChains/ClassicFlang.h b/clang/lib/Driver/ToolChains/ClassicFlang.h
new file mode 100644
index 000000000000..5864e0776601
--- /dev/null
+++ b/clang/lib/Driver/ToolChains/ClassicFlang.h
@@ -0,0 +1,49 @@
+//===--- ClassicFlang.h - Flang ToolChain Implementations -------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_ClassicFlang_H
+#define LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_ClassicFlang_H
+
+#include "MSVC.h"
+#include "clang/Driver/Driver.h"
+#include "clang/Driver/Tool.h"
+#include "clang/Driver/Types.h"
+#include "llvm/Frontend/Debug/Options.h"
+#include "llvm/Option/Option.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/TargetParser/Triple.h"
+
+namespace clang {
+namespace driver {
+
+namespace tools {
+
+/// \brief Flang Fortran frontend
+class LLVM_LIBRARY_VISIBILITY ClassicFlang : public Tool {
+public:
+  ClassicFlang(const ToolChain &TC)
+      : Tool("classic-flang",
+             "Fortran frontend to LLVM", TC) {}
+
+  bool hasGoodDiagnostics() const override { return true; }
+  bool hasIntegratedAssembler() const override { return false; }
+  bool hasIntegratedCPP() const override { return true; }
+
+  void ConstructJob(Compilation &C, const JobAction &JA,
+                    const InputInfo &Output, const InputInfoList &Inputs,
+                    const llvm::opt::ArgList &TCArgs,
+                    const char *LinkingOutput) const override;
+};
+
+} // end namespace tools
+
+} // end namespace driver
+} // end namespace clang
+
+#endif // LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_ClassicFlang_H
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 0d6907b8e5c7..1ccc83a468ce 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -146,6 +146,20 @@ static bool shouldIgnoreUnsupportedTargetFeature(const Arg &TargetFeatureArg,
   return TargetFeatureArg.getOption().matches(options::OPT_mno_cumode);
 }
 
+#ifdef ENABLE_CLASSIC_FLANG
+/// \brief Determine if Fortran "main" object is needed
+bool tools::needFortranMain(const Driver &D, const ArgList &Args) {
+  return (needFortranLibs(D, Args) && !Args.hasArg(options::OPT_Mnomain) &&
+          !Args.hasArg(options::OPT_no_fortran_main));
+}
+
+/// \brief Determine if Fortran link libraies are needed
+bool tools::needFortranLibs(const Driver &D, const ArgList &Args) {
+  return (D.IsFlangMode() && !Args.hasArg(options::OPT_nostdlib) &&
+          !Args.hasArg(options::OPT_noFlangLibs));
+}
+#endif
+
 void tools::addPathIfExists(const Driver &D, const Twine &Path,
                             ToolChain::path_list &Paths) {
   if (D.getVFS().exists(Path))
@@ -256,6 +270,9 @@ void tools::AddLinkerInputs(const ToolChain &TC, const InputInfoList &Inputs,
                             const ArgList &Args, ArgStringList &CmdArgs,
                             const JobAction &JA) {
   const Driver &D = TC.getDriver();
+#ifdef ENABLE_CLASSIC_FLANG
+  bool SeenFirstLinkerInput = false;
+#endif
 
   // Add extra linker input arguments which are not treated as inputs
   // (constructed via -Xarch_).
@@ -289,6 +306,15 @@ void tools::AddLinkerInputs(const ToolChain &TC, const InputInfoList &Inputs,
     if (II.isNothing())
       continue;
 
+#ifdef ENABLE_CLASSIC_FLANG
+    // Add Fortan "main" before the first linker input
+    if (!SeenFirstLinkerInput) {
+      if (needFortranMain(D, Args)) {
+        CmdArgs.push_back("-lflangmain");
+      }
+      SeenFirstLinkerInput = true;
+    }
+#endif
     // Otherwise, this is a linker input argument.
     const Arg &A = II.getInputArg();
 
@@ -300,6 +326,16 @@ void tools::AddLinkerInputs(const ToolChain &TC, const InputInfoList &Inputs,
     else
       A.renderAsInput(Args, CmdArgs);
   }
+#ifdef ENABLE_CLASSIC_FLANG
+  if (!SeenFirstLinkerInput && needFortranMain(D, Args)) {
+    CmdArgs.push_back("-lflangmain");
+  }
+
+  // Claim "no Fortran main" arguments
+  for (auto Arg : Args.filtered(options::OPT_no_fortran_main, options::OPT_Mnomain)) {
+    Arg->claim();
+  }
+#endif
 }
 
 void tools::addLinkerCompressDebugSectionsOption(
@@ -489,10 +525,18 @@ static void getWebAssemblyTargetFeatures(const Driver &D,
                             options::OPT_m_wasm_Features_Group);
 }
 
+#ifndef ENABLE_CLASSIC_FLANG
 void tools::getTargetFeatures(const Driver &D, const llvm::Triple &Triple,
                               const ArgList &Args, ArgStringList &CmdArgs,
                               bool ForAS, bool IsAux) {
   std::vector<StringRef> Features;
+#else
+void tools::getTargetFeatureList(const Driver &D,
+                                 const llvm::Triple &Triple,
+                                 const ArgList &Args, ArgStringList &CmdArgs,
+                                 bool ForAS,
+                                 std::vector<StringRef> &Features) {
+#endif
   switch (Triple.getArch()) {
   default:
     break;
@@ -567,6 +611,15 @@ void tools::getTargetFeatures(const Driver &D, const llvm::Triple &Triple,
     loongarch::getLoongArchTargetFeatures(D, Triple, Args, Features);
     break;
   }
+#ifdef ENABLE_CLASSIC_FLANG
+}
+
+void tools::getTargetFeatures(const Driver &D, const llvm::Triple &Triple,
+                              const ArgList &Args, ArgStringList &CmdArgs,
+                              bool ForAS, bool IsAux) {
+  std::vector<StringRef> Features;
+  getTargetFeatureList(D, Triple, Args, CmdArgs, ForAS, Features);
+#endif
 
   for (auto Feature : unifyTargetFeatures(Features)) {
     CmdArgs.push_back(IsAux ? "-aux-target-feature" : "-target-feature");
@@ -889,7 +942,11 @@ bool tools::addOpenMPRuntime(ArgStringList &CmdArgs, const ToolChain &TC,
                              const ArgList &Args, bool ForceStaticHostRuntime,
                              bool IsOffloadingHost, bool GompNeedsRT) {
   if (!Args.hasFlag(options::OPT_fopenmp, options::OPT_fopenmp_EQ,
-                    options::OPT_fno_openmp, false))
+                    options::OPT_fno_openmp, false)
+#ifdef ENABLE_CLASSIC_FLANG
+      && !Args.hasFlag(options::OPT_mp, options::OPT_nomp, false)
+#endif
+     )
     return false;
 
   Driver::OpenMPRuntimeKind RTKind = TC.getDriver().getOpenMPRuntime(Args);
@@ -934,7 +991,16 @@ bool tools::addOpenMPRuntime(ArgStringList &CmdArgs, const ToolChain &TC,
 }
 
 void tools::addFortranRuntimeLibs(const ToolChain &TC,
+#ifdef ENABLE_CLASSIC_FLANG
+                                  const llvm::opt::ArgList &Args,
+#endif
                                   llvm::opt::ArgStringList &CmdArgs) {
+#ifdef ENABLE_CLASSIC_FLANG
+  if (needFortranLibs(TC.getDriver(), Args))
+    TC.AddFortranStdlibLibArgs(Args, CmdArgs);
+  else
+    Args.ClaimAllArgs(options::OPT_noFlangLibs);
+#else
   if (TC.getTriple().isKnownWindowsMSVCEnvironment()) {
     CmdArgs.push_back("Fortran_main.lib");
     CmdArgs.push_back("FortranRuntime.lib");
@@ -944,6 +1010,7 @@ void tools::addFortranRuntimeLibs(const ToolChain &TC,
     CmdArgs.push_back("-lFortranRuntime");
     CmdArgs.push_back("-lFortranDecimal");
   }
+#endif
 }
 
 void tools::addFortranRuntimeLibraryPath(const ToolChain &TC,
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.h b/clang/lib/Driver/ToolChains/CommonArgs.h
index 6a8de0f1c36d..bd5cb1bb866e 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.h
+++ b/clang/lib/Driver/ToolChains/CommonArgs.h
@@ -23,6 +23,12 @@ namespace clang {
 namespace driver {
 namespace tools {
 
+#ifdef ENABLE_CLASSIC_FLANG
+bool needFortranLibs(const Driver &D, const llvm::opt::ArgList &Args);
+
+bool needFortranMain(const Driver &D, const llvm::opt::ArgList &Args);
+#endif
+
 void addPathIfExists(const Driver &D, const Twine &Path,
                      ToolChain::path_list &Paths);
 
@@ -131,6 +137,9 @@ bool addOpenMPRuntime(llvm::opt::ArgStringList &CmdArgs, const ToolChain &TC,
 
 /// Adds Fortran runtime libraries to \p CmdArgs.
 void addFortranRuntimeLibs(const ToolChain &TC,
+#ifdef ENABLE_CLASSIC_FLANG
+                           const llvm::opt::ArgList &Args,
+#endif
                            llvm::opt::ArgStringList &CmdArgs);
 
 /// Adds the path for the Fortran runtime libraries to \p CmdArgs.
@@ -173,6 +182,17 @@ void AddTargetFeature(const llvm::opt::ArgList &Args,
 std::string getCPUName(const Driver &D, const llvm::opt::ArgList &Args,
                        const llvm::Triple &T, bool FromAs = false);
 
+#ifdef ENABLE_CLASSIC_FLANG
+// Helper function extracted from upstream getTargetFeatures. Classic Flang
+// uses this helper to render the target feature options for the Fortran
+// frontend.
+void getTargetFeatureList(const Driver &D,
+                          const llvm::Triple &Triple,
+                          const llvm::opt::ArgList &Args,
+                          llvm::opt::ArgStringList &CmdArgs,
+                          bool ForAS, std::vector<StringRef> &Features);
+#endif
+
 void getTargetFeatures(const Driver &D, const llvm::Triple &Triple,
                        const llvm::opt::ArgList &Args,
                        llvm::opt::ArgStringList &CmdArgs, bool ForAS,
diff --git a/clang/lib/Driver/ToolChains/Cuda.cpp b/clang/lib/Driver/ToolChains/Cuda.cpp
index 3a577650eb08..36fddca2d177 100644
--- a/clang/lib/Driver/ToolChains/Cuda.cpp
+++ b/clang/lib/Driver/ToolChains/Cuda.cpp
@@ -1034,3 +1034,38 @@ VersionTuple CudaToolChain::computeMSVCVersion(const Driver *D,
                                                const ArgList &Args) const {
   return HostTC.computeMSVCVersion(D, Args);
 }
+
+#ifdef ENABLE_CLASSIC_FLANG
+static void AddFlangSysIncludeArg(const ArgList &DriverArgs,
+                                  ArgStringList &Flang1Args,
+                                  ToolChain::path_list IncludePathList) {
+  std::string ArgValue; // Path argument value
+
+  // Make up argument value consisting of paths separated by colons
+  bool first = true;
+  for (auto P : IncludePathList) {
+    if (first) {
+      first = false;
+    } else {
+      ArgValue += ":";
+    }
+    ArgValue += P;
+  }
+
+  // Add the argument
+  Flang1Args.push_back("-stdinc");
+  Flang1Args.push_back(DriverArgs.MakeArgString(ArgValue));
+}
+
+void CudaToolChain::AddFlangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
+                                              llvm::opt::ArgStringList &Flang1Args) const {
+  path_list IncludePathList;
+  const Driver &D = getDriver();
+  if (DriverArgs.hasArg(options::OPT_nostdinc))
+    return;
+  SmallString<128> P(D.InstalledDir);
+  llvm::sys::path::append(P, "../include");
+  IncludePathList.push_back(P.c_str());
+  AddFlangSysIncludeArg(DriverArgs, Flang1Args, IncludePathList);
+}
+#endif
diff --git a/clang/lib/Driver/ToolChains/Cuda.h b/clang/lib/Driver/ToolChains/Cuda.h
index 39df6e06fb26..3eded1f53e42 100644
--- a/clang/lib/Driver/ToolChains/Cuda.h
+++ b/clang/lib/Driver/ToolChains/Cuda.h
@@ -214,6 +214,11 @@ public:
       llvm::opt::ArgStringList &CC1Args) const override;
   void AddIAMCUIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                            llvm::opt::ArgStringList &CC1Args) const override;
+#ifdef ENABLE_CLASSIC_FLANG
+  void
+  AddFlangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
+                            llvm::opt::ArgStringList &Flang1Args) const override;
+#endif
 
   SanitizerMask getSupportedSanitizers() const override;
 
diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
index 65bd6c6a7eb3..3b8e4d7e133a 100644
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -679,7 +679,11 @@ void darwin::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   // to generate executables.
   if (getToolChain().getDriver().IsFlangMode()) {
     addFortranRuntimeLibraryPath(getToolChain(), Args, CmdArgs);
+#ifdef ENABLE_CLASSIC_FLANG
+    addFortranRuntimeLibs(getToolChain(), Args, CmdArgs);
+#else
     addFortranRuntimeLibs(getToolChain(), CmdArgs);
+#endif
   }
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs))
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
index 0bb5433a658a..076a2d4a21d8 100644
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -578,7 +578,11 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   // AddRuntTimeLibs).
   if (D.IsFlangMode()) {
     addFortranRuntimeLibraryPath(ToolChain, Args, CmdArgs);
+#ifdef ENABLE_CLASSIC_FLANG
+    addFortranRuntimeLibs(ToolChain, Args, CmdArgs);
+#else
     addFortranRuntimeLibs(ToolChain, CmdArgs);
+#endif
     CmdArgs.push_back("-lm");
   }
 
diff --git a/clang/lib/Driver/ToolChains/Linux.cpp b/clang/lib/Driver/ToolChains/Linux.cpp
index 1ba222bf83b1..7f0714676a9d 100644
--- a/clang/lib/Driver/ToolChains/Linux.cpp
+++ b/clang/lib/Driver/ToolChains/Linux.cpp
@@ -608,6 +608,196 @@ std::string Linux::getDynamicLinker(const ArgList &Args) const {
   return "/" + LibDir + "/" + Loader;
 }
 
+#ifdef ENABLE_CLASSIC_FLANG
+/// Convert path list to Fortran frontend argument
+static void AddFlangSysIncludeArg(const ArgList &DriverArgs,
+                                  ArgStringList &Flang1Args,
+                                  ToolChain::path_list IncludePathList) {
+  std::string ArgValue; // Path argument value
+
+  // Make up argument value consisting of paths separated by colons
+  bool first = true;
+  for (auto P : IncludePathList) {
+    if (first) {
+      first = false;
+    } else {
+      ArgValue += ":";
+    }
+    ArgValue += P;
+  }
+
+  // Add the argument
+  Flang1Args.push_back("-stdinc");
+  Flang1Args.push_back(DriverArgs.MakeArgString(ArgValue));
+}
+
+void Linux::AddFlangSystemIncludeArgs(const ArgList &DriverArgs,
+                                      ArgStringList &Flang1Args) const {
+  path_list IncludePathList;
+  const Driver &D = getDriver();
+  std::string SysRoot = computeSysRoot();
+
+  if (DriverArgs.hasArg(options::OPT_nostdinc))
+    return;
+
+  {
+    SmallString<128> P(D.InstalledDir);
+    llvm::sys::path::append(P, "../include");
+    IncludePathList.push_back(P.c_str());
+  }
+
+  if (!DriverArgs.hasArg(options::OPT_nostdlibinc))
+    IncludePathList.push_back(SysRoot + "/usr/local/include");
+
+  if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
+    SmallString<128> P(D.ResourceDir);
+    llvm::sys::path::append(P, "include");
+    IncludePathList.push_back(P.c_str());
+  }
+
+  if (DriverArgs.hasArg(options::OPT_nostdlibinc)) {
+    AddFlangSysIncludeArg(DriverArgs, Flang1Args, IncludePathList);
+    return;
+  }
+
+  // Check for configure-time C include directories.
+  StringRef CIncludeDirs(C_INCLUDE_DIRS);
+  if (CIncludeDirs != "") {
+    SmallVector<StringRef, 5> dirs;
+    CIncludeDirs.split(dirs, ":");
+    for (StringRef dir : dirs) {
+      StringRef Prefix =
+          llvm::sys::path::is_absolute(dir) ? StringRef(SysRoot) : "";
+      IncludePathList.push_back(Prefix.str() + dir.str());
+    }
+    AddFlangSysIncludeArg(DriverArgs, Flang1Args, IncludePathList);
+    return;
+  }
+
+  // Lacking those, try to detect the correct set of system includes for the
+  // target triple.
+
+  // Add include directories specific to the selected multilib set and multilib.
+  if (GCCInstallation.isValid()) {
+    const auto &Callback = Multilibs.includeDirsCallback();
+    if (Callback) {
+      for (const auto &Path : Callback(GCCInstallation.getMultilib()))
+        addExternCSystemIncludeIfExists(
+            DriverArgs, Flang1Args, GCCInstallation.getInstallPath() + Path);
+    }
+  }
+
+  // Implement generic Debian multiarch support.
+  const StringRef X86_64MultiarchIncludeDirs[] = {
+      "/usr/include/x86_64-linux-gnu",
+
+      // FIXME: These are older forms of multiarch. It's not clear that they're
+      // in use in any released version of Debian, so we should consider
+      // removing them.
+      "/usr/include/i686-linux-gnu/64", "/usr/include/i486-linux-gnu/64"};
+  const StringRef X86MultiarchIncludeDirs[] = {
+      "/usr/include/i386-linux-gnu",
+
+      // FIXME: These are older forms of multiarch. It's not clear that they're
+      // in use in any released version of Debian, so we should consider
+      // removing them.
+      "/usr/include/x86_64-linux-gnu/32", "/usr/include/i686-linux-gnu",
+      "/usr/include/i486-linux-gnu"};
+  const StringRef AArch64MultiarchIncludeDirs[] = {
+      "/usr/include/aarch64-linux-gnu"};
+  const StringRef ARMMultiarchIncludeDirs[] = {
+      "/usr/include/arm-linux-gnueabi"};
+  const StringRef ARMHFMultiarchIncludeDirs[] = {
+      "/usr/include/arm-linux-gnueabihf"};
+  const StringRef MIPSMultiarchIncludeDirs[] = {"/usr/include/mips-linux-gnu"};
+  const StringRef MIPSELMultiarchIncludeDirs[] = {
+      "/usr/include/mipsel-linux-gnu"};
+  const StringRef MIPS64MultiarchIncludeDirs[] = {
+      "/usr/include/mips64-linux-gnu", "/usr/include/mips64-linux-gnuabi64"};
+  const StringRef MIPS64ELMultiarchIncludeDirs[] = {
+      "/usr/include/mips64el-linux-gnu",
+      "/usr/include/mips64el-linux-gnuabi64"};
+  const StringRef PPCMultiarchIncludeDirs[] = {
+      "/usr/include/powerpc-linux-gnu"};
+  const StringRef PPC64MultiarchIncludeDirs[] = {
+      "/usr/include/powerpc64-linux-gnu"};
+  const StringRef PPC64LEMultiarchIncludeDirs[] = {
+      "/usr/include/powerpc64le-linux-gnu"};
+  const StringRef SparcMultiarchIncludeDirs[] = {
+      "/usr/include/sparc-linux-gnu"};
+  const StringRef Sparc64MultiarchIncludeDirs[] = {
+      "/usr/include/sparc64-linux-gnu"};
+  ArrayRef<StringRef> MultiarchIncludeDirs;
+  switch (getTriple().getArch()) {
+  case llvm::Triple::x86_64:
+    MultiarchIncludeDirs = X86_64MultiarchIncludeDirs;
+    break;
+  case llvm::Triple::x86:
+    MultiarchIncludeDirs = X86MultiarchIncludeDirs;
+    break;
+  case llvm::Triple::aarch64:
+  case llvm::Triple::aarch64_be:
+    MultiarchIncludeDirs = AArch64MultiarchIncludeDirs;
+    break;
+  case llvm::Triple::arm:
+    if (getTriple().getEnvironment() == llvm::Triple::GNUEABIHF)
+      MultiarchIncludeDirs = ARMHFMultiarchIncludeDirs;
+    else
+      MultiarchIncludeDirs = ARMMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::mips:
+    MultiarchIncludeDirs = MIPSMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::mipsel:
+    MultiarchIncludeDirs = MIPSELMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::mips64:
+    MultiarchIncludeDirs = MIPS64MultiarchIncludeDirs;
+    break;
+  case llvm::Triple::mips64el:
+    MultiarchIncludeDirs = MIPS64ELMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::ppc:
+    MultiarchIncludeDirs = PPCMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::ppc64:
+    MultiarchIncludeDirs = PPC64MultiarchIncludeDirs;
+    break;
+  case llvm::Triple::ppc64le:
+    MultiarchIncludeDirs = PPC64LEMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::sparc:
+    MultiarchIncludeDirs = SparcMultiarchIncludeDirs;
+    break;
+  case llvm::Triple::sparcv9:
+    MultiarchIncludeDirs = Sparc64MultiarchIncludeDirs;
+    break;
+  default:
+    break;
+  }
+  for (StringRef Dir : MultiarchIncludeDirs) {
+    if (llvm::sys::fs::exists(SysRoot + Dir)) {
+      IncludePathList.push_back(SysRoot + Dir.str());
+      break;
+    }
+  }
+
+  if (getTriple().getOS() == llvm::Triple::RTEMS) {
+    AddFlangSysIncludeArg(DriverArgs, Flang1Args, IncludePathList);
+    return;
+  }
+
+  // Add an include of '/include' directly. This isn't provided by default by
+  // system GCCs, but is often used with cross-compiling GCCs, and harmless to
+  // add even when Clang is acting as-if it were a system compiler.
+  IncludePathList.push_back(SysRoot + "/include");
+
+  IncludePathList.push_back(SysRoot + "/usr/include");
+
+  AddFlangSysIncludeArg(DriverArgs, Flang1Args, IncludePathList);
+}
+#endif
+
 void Linux::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
                                       ArgStringList &CC1Args) const {
   const Driver &D = getDriver();
diff --git a/clang/lib/Driver/ToolChains/Linux.h b/clang/lib/Driver/ToolChains/Linux.h
index 524391743090..b6db4160811d 100644
--- a/clang/lib/Driver/ToolChains/Linux.h
+++ b/clang/lib/Driver/ToolChains/Linux.h
@@ -27,6 +27,11 @@ public:
                                  const llvm::Triple &TargetTriple,
                                  StringRef SysRoot) const override;
 
+#ifdef ENABLE_CLASSIC_FLANG
+  void
+  AddFlangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
+                           llvm::opt::ArgStringList &Flang1Args) const override;
+#endif
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
diff --git a/clang/lib/Driver/ToolChains/MSVC.cpp b/clang/lib/Driver/ToolChains/MSVC.cpp
index a9fe9da4620f..1562e1a4b8eb 100644
--- a/clang/lib/Driver/ToolChains/MSVC.cpp
+++ b/clang/lib/Driver/ToolChains/MSVC.cpp
@@ -131,7 +131,11 @@ void visualstudio::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   if (C.getDriver().IsFlangMode()) {
     addFortranRuntimeLibraryPath(TC, Args, CmdArgs);
+#ifdef ENABLE_CLASSIC_FLANG
+    addFortranRuntimeLibs(TC, Args, CmdArgs);
+#else
     addFortranRuntimeLibs(TC, CmdArgs);
+#endif
 
     // Inform the MSVC linker that we're generating a console application, i.e.
     // one with `main` as the "user-defined" entry point. The `main` function is
@@ -263,6 +267,13 @@ void visualstudio::Linker::ConstructJob(Compilation &C, const JobAction &JA,
     }
   }
 
+#ifdef ENABLE_CLASSIC_FLANG
+  if (C.getDriver().IsFlangMode()) {
+    CmdArgs.push_back(Args.MakeArgString(std::string("-libpath:") +
+                                         TC.getDriver().Dir + "/../lib"));
+  }
+#endif
+
   // Add compiler-rt lib in case if it was explicitly
   // specified as an argument for --rtlib option.
   if (!Args.hasArg(options::OPT_nostdlib)) {
@@ -510,6 +521,74 @@ void MSVCToolChain::AddHIPRuntimeLibArgs(const ArgList &Args,
                   "amdhip64.lib"});
 }
 
+#ifdef ENABLE_CLASSIC_FLANG
+void MSVCToolChain::AddFortranStdlibLibArgs(const ArgList &Args,
+                                    ArgStringList &CmdArgs) const {
+ bool staticFlangLibs = false;
+ bool useOpenMP = false;
+
+  if (Args.hasArg(options::OPT_staticFlangLibs)) {
+    for (auto *A: Args.filtered(options::OPT_staticFlangLibs)) {
+      A->claim();
+      staticFlangLibs = true;
+    }
+  }
+
+  Arg *A = Args.getLastArg(options::OPT_mp, options::OPT_nomp,
+                           options::OPT_fopenmp, options::OPT_fno_openmp);
+  if (A &&
+      (A->getOption().matches(options::OPT_mp) ||
+       A->getOption().matches(options::OPT_fopenmp))) {
+      useOpenMP = true;
+  }
+
+  if (needFortranMain(getDriver(), Args)) {
+    // flangmain is always static
+    CmdArgs.push_back("-linker");
+    CmdArgs.push_back("/subsystem:console");
+    CmdArgs.push_back("-linker");
+    CmdArgs.push_back("/defaultlib:flangmain.lib");
+  }
+
+  if (staticFlangLibs) {
+    CmdArgs.push_back("-linker");
+    CmdArgs.push_back("/defaultlib:libflang.lib");
+    CmdArgs.push_back("-linker");
+    CmdArgs.push_back("/defaultlib:libflangrti.lib");
+    CmdArgs.push_back("-linker");
+    CmdArgs.push_back("/defaultlib:libpgmath.lib");
+  } else {
+    CmdArgs.push_back("-linker");
+    CmdArgs.push_back("/defaultlib:flang.lib");
+    CmdArgs.push_back("-linker");
+    CmdArgs.push_back("/defaultlib:flangrti.lib");
+    CmdArgs.push_back("-linker");
+    CmdArgs.push_back("/defaultlib:pgmath.lib");
+  }
+  if (useOpenMP) {
+    CmdArgs.push_back("-linker");
+    CmdArgs.push_back("/nodefaultlib:vcomp.lib");
+    CmdArgs.push_back("-linker");
+    CmdArgs.push_back("/nodefaultlib:vcompd.lib");
+    CmdArgs.push_back("-linker");
+    CmdArgs.push_back("/defaultlib:libomp.lib");
+  }
+
+  // Allways link Fortran executables with Pthreads
+  // CmdArgs.push_back("-lpthread");
+
+  // These options are added clang-cl in Clang.cpp for C/C++
+  // In clang-cl.exe -MD and -MT control these options, but in
+  // flang.exe like clang.exe these are different options for
+  // dependency tracking. Let's assume that if somebody needs
+  // static flang libs, they don't need static C runtime libs.
+  // FIXME: Use LLVM_USE_CRT_<CMAKE_BUILD_TYPE> variable
+  // to use libcmt.lib or msvcrt.lib
+  CmdArgs.push_back("-linker");
+  CmdArgs.push_back("/defaultlib:libcmt.lib");
+}
+#endif
+
 void MSVCToolChain::printVerboseInfo(raw_ostream &OS) const {
   CudaInstallation.print(OS);
   RocmInstallation.print(OS);
@@ -634,6 +713,42 @@ void MSVCToolChain::AddSystemIncludeWithSubfolder(
   addSystemInclude(DriverArgs, CC1Args, path);
 }
 
+#ifdef ENABLE_CLASSIC_FLANG
+/// Convert path list to Fortran frontend argument
+static void AddFlangSysIncludeArg(const ArgList &DriverArgs,
+                                  ArgStringList &Flang1Args,
+                                  ToolChain::path_list IncludePathList) {
+  std::string ArgValue; // Path argument value
+
+  // Make up argument value consisting of paths separated by colons
+  bool first = true;
+  for (auto P : IncludePathList) {
+    if (first) {
+      first = false;
+    } else {
+      ArgValue += ";";
+    }
+    ArgValue += P;
+  }
+
+  // Add the argument
+  Flang1Args.push_back("-stdinc");
+  Flang1Args.push_back(DriverArgs.MakeArgString(ArgValue));
+}
+
+void MSVCToolChain::AddFlangSystemIncludeArgs(const ArgList &DriverArgs,
+                                      ArgStringList &Flang1Args) const {
+path_list IncludePathList;
+  const Driver &D = getDriver();
+  if (DriverArgs.hasArg(options::OPT_nostdinc))
+    return;
+  SmallString<128> P(D.InstalledDir);
+  llvm::sys::path::append(P, "../include");
+  IncludePathList.push_back(P.c_str());
+  AddFlangSysIncludeArg(DriverArgs, Flang1Args, IncludePathList);
+}
+#endif
+
 void MSVCToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
                                               ArgStringList &CC1Args) const {
   if (DriverArgs.hasArg(options::OPT_nostdinc))
diff --git a/clang/lib/Driver/ToolChains/MSVC.h b/clang/lib/Driver/ToolChains/MSVC.h
index 0f687bc70ae4..46d5af9d114f 100644
--- a/clang/lib/Driver/ToolChains/MSVC.h
+++ b/clang/lib/Driver/ToolChains/MSVC.h
@@ -84,6 +84,12 @@ public:
     return VSLayout == llvm::ToolsetLayout::VS2017OrNewer;
   }
 
+#ifdef ENABLE_CLASSIC_FLANG
+  void
+  AddFlangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
+                           llvm::opt::ArgStringList &Flang1Args) const override;
+#endif
+
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
@@ -100,6 +106,11 @@ public:
   void AddHIPRuntimeLibArgs(const llvm::opt::ArgList &Args,
                             llvm::opt::ArgStringList &CmdArgs) const override;
 
+#ifdef ENABLE_CLASSIC_FLANG
+  void AddFortranStdlibLibArgs(const llvm::opt::ArgList &Args,
+                               llvm::opt::ArgStringList &CmdArgs) const override;
+#endif
+
   bool getWindowsSDKLibraryPath(
       const llvm::opt::ArgList &Args, std::string &path) const;
   bool getUniversalCRTLibraryPath(const llvm::opt::ArgList &Args,
diff --git a/clang/lib/Driver/ToolChains/MinGW.cpp b/clang/lib/Driver/ToolChains/MinGW.cpp
index 503dbf3f0dea..264cc7ab06c8 100644
--- a/clang/lib/Driver/ToolChains/MinGW.cpp
+++ b/clang/lib/Driver/ToolChains/MinGW.cpp
@@ -240,7 +240,11 @@ void tools::MinGW::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   if (C.getDriver().IsFlangMode()) {
     addFortranRuntimeLibraryPath(TC, Args, CmdArgs);
+#ifdef ENABLE_CLASSIC_FLANG
+    addFortranRuntimeLibs(TC, Args, CmdArgs);
+#else
     addFortranRuntimeLibs(TC, CmdArgs);
+#endif
   }
 
   // TODO: Add profile stuff here
diff --git a/clang/lib/Driver/Types.cpp b/clang/lib/Driver/Types.cpp
old mode 100644
new mode 100755
index 7d6308d757bc..a10c6e2c6c42
--- a/clang/lib/Driver/Types.cpp
+++ b/clang/lib/Driver/Types.cpp
@@ -55,9 +55,11 @@ const char *types::getTypeName(ID Id) {
 
 types::ID types::getPreprocessedType(ID Id) {
   ID PPT = getInfo(Id).PreprocessedType;
+#ifndef ENABLE_CLASSIC_FLANG
   assert((getInfo(Id).Phases.contains(phases::Preprocess) !=
           (PPT == TY_INVALID)) &&
          "Unexpected Preprocess Type.");
+#endif
   return PPT;
 }
 
@@ -134,6 +136,10 @@ bool types::isAcceptedByClang(ID Id) {
   case TY_Asm:
   case TY_C: case TY_PP_C:
   case TY_CL: case TY_CLCXX:
+#ifdef ENABLE_CLASSIC_FLANG
+  case TY_F_FreeForm: case TY_PP_F_FreeForm:
+  case TY_F_FixedForm: case TY_PP_F_FixedForm:
+#endif
   case TY_CUDA: case TY_PP_CUDA:
   case TY_CUDA_DEVICE:
   case TY_HIP:
@@ -164,12 +170,20 @@ bool types::isAcceptedByFlang(ID Id) {
   default:
     return false;
 
+#ifdef ENABLE_CLASSIC_FLANG
+  case TY_F_FreeForm:
+  case TY_PP_F_FreeForm:
+  case TY_F_FixedForm:
+  case TY_PP_F_FixedForm:
+    return true;
+#else
   case TY_Fortran:
   case TY_PP_Fortran:
     return true;
   case TY_LLVM_IR:
   case TY_LLVM_BC:
     return true;
+#endif
   }
 }
 
@@ -286,6 +300,22 @@ bool types::isHIP(ID Id) {
   }
 }
 
+#ifdef ENABLE_CLASSIC_FLANG
+bool types::isFreeFormFortran(ID Id) {
+  if (!isAcceptedByFlang(Id))
+    return false;
+
+  return (Id == TY_F_FreeForm || Id == TY_PP_F_FreeForm);
+}
+
+bool types::isFixedFormFortran(ID Id) {
+  if (!isAcceptedByFlang(Id))
+    return false;
+
+  return (Id == TY_F_FixedForm || Id == TY_PP_F_FixedForm);
+}
+#endif
+
 bool types::isHLSL(ID Id) { return Id == TY_HLSL; }
 
 bool types::isSrcFile(ID Id) {
@@ -296,8 +326,13 @@ types::ID types::lookupTypeForExtension(llvm::StringRef Ext) {
   return llvm::StringSwitch<types::ID>(Ext)
       .Case("c", TY_C)
       .Case("C", TY_CXX)
+#ifdef ENABLE_CLASSIC_FLANG
+      .Case("F", TY_F_FixedForm)
+      .Case("f", TY_PP_F_FixedForm)
+#else
       .Case("F", TY_Fortran)
       .Case("f", TY_PP_Fortran)
+#endif
       .Case("h", TY_CHeader)
       .Case("H", TY_CXXHeader)
       .Case("i", TY_PP_C)
@@ -331,6 +366,20 @@ types::ID types::lookupTypeForExtension(llvm::StringRef Ext) {
       .Case("cui", TY_PP_CUDA)
       .Case("cxx", TY_CXX)
       .Case("CXX", TY_CXX)
+#ifdef ENABLE_CLASSIC_FLANG
+      .Case("for", TY_PP_F_FixedForm)
+      .Case("FOR", TY_PP_F_FixedForm)
+      .Case("fpp", TY_F_FixedForm)
+      .Case("FPP", TY_F_FixedForm)
+      .Case("f90", TY_PP_F_FreeForm)
+      .Case("f95", TY_PP_F_FreeForm)
+      .Case("f03", TY_PP_F_FreeForm)
+      .Case("f08", TY_PP_F_FreeForm)
+      .Case("F90", TY_F_FreeForm)
+      .Case("F95", TY_F_FreeForm)
+      .Case("F03", TY_F_FreeForm)
+      .Case("F08", TY_F_FreeForm)
+#else
       .Case("F03", TY_Fortran)
       .Case("f03", TY_PP_Fortran)
       .Case("F08", TY_Fortran)
@@ -343,6 +392,7 @@ types::ID types::lookupTypeForExtension(llvm::StringRef Ext) {
       .Case("FOR", TY_PP_Fortran)
       .Case("fpp", TY_Fortran)
       .Case("FPP", TY_Fortran)
+#endif
       .Case("gch", TY_PCH)
       .Case("hip", TY_HIP)
       .Case("hipi", TY_PP_HIP)
diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index f8fae82fba12..7b01cb01a45e 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -161,26 +161,6 @@ static void DefineFloatMacros(MacroBuilder &Builder, StringRef Prefix,
   Builder.defineMacro(DefPrefix + "MIN__", Twine(Min)+Ext);
 }
 
-
-/// DefineTypeSize - Emit a macro to the predefines buffer that declares a macro
-/// named MacroName with the max value for a type with width 'TypeWidth' a
-/// signedness of 'isSigned' and with a value suffix of 'ValSuffix' (e.g. LL).
-static void DefineTypeSize(const Twine &MacroName, unsigned TypeWidth,
-                           StringRef ValSuffix, bool isSigned,
-                           MacroBuilder &Builder) {
-  llvm::APInt MaxVal = isSigned ? llvm::APInt::getSignedMaxValue(TypeWidth)
-                                : llvm::APInt::getMaxValue(TypeWidth);
-  Builder.defineMacro(MacroName, toString(MaxVal, 10, isSigned) + ValSuffix);
-}
-
-/// DefineTypeSize - An overloaded helper that uses TargetInfo to determine
-/// the width, suffix, and signedness of the given type
-static void DefineTypeSize(const Twine &MacroName, TargetInfo::IntType Ty,
-                           const TargetInfo &TI, MacroBuilder &Builder) {
-  DefineTypeSize(MacroName, TI.getTypeWidth(Ty), TI.getTypeConstantSuffix(Ty),
-                 TI.isTypeSigned(Ty), Builder);
-}
-
 static void DefineFmt(const Twine &Prefix, TargetInfo::IntType Ty,
                       const TargetInfo &TI, MacroBuilder &Builder) {
   bool IsSigned = TI.isTypeSigned(Ty);
diff --git a/clang/test/CMakeLists.txt b/clang/test/CMakeLists.txt
index 31b494f39cce..b88694deb818 100644
--- a/clang/test/CMakeLists.txt
+++ b/clang/test/CMakeLists.txt
@@ -10,6 +10,7 @@ llvm_canonicalize_cmake_booleans(
   CLANG_PLUGIN_SUPPORT
   CLANG_SPAWN_CC1
   ENABLE_BACKTRACES
+  LLVM_ENABLE_CLASSIC_FLANG
   LLVM_ENABLE_ZLIB
   LLVM_ENABLE_ZSTD
   LLVM_ENABLE_PER_TARGET_RUNTIME_DIR
diff --git a/clang/test/CodeGen/libpgmath-logfun-aarch64.ll b/clang/test/CodeGen/libpgmath-logfun-aarch64.ll
new file mode 100644
index 000000000000..141fed29ccd1
--- /dev/null
+++ b/clang/test/CodeGen/libpgmath-logfun-aarch64.ll
@@ -0,0 +1,58 @@
+; REQUIRES: aarch64-registered-target
+
+; RUN: %clang -target aarch64-unknown-linux-gnu -Ofast -S %s -o - | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @fun_(i64* nocapture %z) local_unnamed_addr #0 {
+L.entry:
+  %0 = bitcast i64* %z to i8*
+  %1 = bitcast i64* %z to float*
+  %2 = load float, float* %1, align 4
+  %3 = fpext float %2 to double
+  %4 = fadd double %3, 5.000000e-01
+  %5 = tail call double @__pd_log_1(double %4) #1
+  %6 = fptrunc double %5 to float
+  %7 = tail call float @__ps_exp_1(float %6) #2
+  store float %7, float* %1, align 4
+  %8 = getelementptr i8, i8* %0, i64 4
+  %9 = bitcast i8* %8 to float*
+  %10 = load float, float* %9, align 4
+  %11 = fpext float %10 to double
+  %12 = fadd double %11, 5.000000e-01
+  %13 = tail call double @__pd_log_1(double %12) #1
+  %14 = fptrunc double %13 to float
+  %15 = tail call float @__ps_exp_1(float %14) #2
+  store float %15, float* %9, align 4
+  %16 = getelementptr i64, i64* %z, i64 1
+  %17 = bitcast i64* %16 to float*
+  %18 = load float, float* %17, align 4
+  %19 = fpext float %18 to double
+  %20 = fadd double %19, 5.000000e-01
+  %21 = tail call double @__pd_log_1(double %20) #1
+  %22 = fptrunc double %21 to float
+  %23 = tail call float @__ps_exp_1(float %22) #2
+  store float %23, float* %17, align 4
+  %24 = getelementptr i8, i8* %0, i64 12
+  %25 = bitcast i8* %24 to float*
+  %26 = load float, float* %25, align 4
+  %27 = fpext float %26 to double
+  %28 = fadd double %27, 5.000000e-01
+  %29 = tail call double @__pd_log_1(double %28) #1
+  %30 = fptrunc double %29 to float
+  %31 = tail call float @__ps_exp_1(float %30) #2
+  store float %31, float* %25, align 4
+  ret void
+
+; CHECK-NOT: __pd_log_4
+; CHECK: __pd_log_2
+; CHECK: __pd_log_2
+}
+
+; Function Attrs: nounwind readnone willreturn
+declare float @__ps_exp_1(float) #0
+
+; Function Attrs: nounwind readnone willreturn
+declare double @__pd_log_1(double) #0
+
+attributes #0 = { nounwind readnone willreturn }
diff --git a/clang/test/CodeGen/libpgmath-logfun-x86_64.ll b/clang/test/CodeGen/libpgmath-logfun-x86_64.ll
new file mode 100644
index 000000000000..3ce1d910947f
--- /dev/null
+++ b/clang/test/CodeGen/libpgmath-logfun-x86_64.ll
@@ -0,0 +1,57 @@
+; REQUIRES: x86-registered-target
+
+; RUN: %clang -target x86_64-unknown-linux-gnu -msse -Ofast -S %s -o - | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @fun_(i64* nocapture %z) local_unnamed_addr #0 {
+L.entry:
+  %0 = bitcast i64* %z to i8*
+  %1 = bitcast i64* %z to float*
+  %2 = load float, float* %1, align 4
+  %3 = fpext float %2 to double
+  %4 = fadd double %3, 5.000000e-01
+  %5 = tail call double @__pd_log_1(double %4) #1
+  %6 = fptrunc double %5 to float
+  %7 = tail call float @__ps_exp_1(float %6) #2
+  store float %7, float* %1, align 4
+  %8 = getelementptr i8, i8* %0, i64 4
+  %9 = bitcast i8* %8 to float*
+  %10 = load float, float* %9, align 4
+  %11 = fpext float %10 to double
+  %12 = fadd double %11, 5.000000e-01
+  %13 = tail call double @__pd_log_1(double %12) #1
+  %14 = fptrunc double %13 to float
+  %15 = tail call float @__ps_exp_1(float %14) #2
+  store float %15, float* %9, align 4
+  %16 = getelementptr i64, i64* %z, i64 1
+  %17 = bitcast i64* %16 to float*
+  %18 = load float, float* %17, align 4
+  %19 = fpext float %18 to double
+  %20 = fadd double %19, 5.000000e-01
+  %21 = tail call double @__pd_log_1(double %20) #1
+  %22 = fptrunc double %21 to float
+  %23 = tail call float @__ps_exp_1(float %22) #2
+  store float %23, float* %17, align 4
+  %24 = getelementptr i8, i8* %0, i64 12
+  %25 = bitcast i8* %24 to float*
+  %26 = load float, float* %25, align 4
+  %27 = fpext float %26 to double
+  %28 = fadd double %27, 5.000000e-01
+  %29 = tail call double @__pd_log_1(double %28) #1
+  %30 = fptrunc double %29 to float
+  %31 = tail call float @__ps_exp_1(float %30) #2
+  store float %31, float* %25, align 4
+  ret void
+
+; CHECK-NOT: __pd_log_1
+; CHECK: __pd_log_4
+}
+
+; Function Attrs: nounwind readnone willreturn
+declare float @__ps_exp_1(float) #0
+
+; Function Attrs: nounwind readnone willreturn
+declare double @__pd_log_1(double) #0
+
+attributes #0 = { nounwind readnone willreturn }
diff --git a/clang/test/Driver/autocomplete.c b/clang/test/Driver/autocomplete.c
index d6f57708b67e..8c4921c9dbd5 100644
--- a/clang/test/Driver/autocomplete.c
+++ b/clang/test/Driver/autocomplete.c
@@ -85,7 +85,7 @@
 // FVECLIBALL-NEXT: libmvec
 // FVECLIBALL-NEXT: MASSV
 // FVECLIBALL-NEXT: none
-// FVECLIBALL-NEXT: SLEEF
+// FVECLIBALL:      SLEEF
 // FVECLIBALL-NEXT: SVML
 // RUN: %clang --autocomplete=-fshow-overloads= | FileCheck %s -check-prefix=FSOVERALL
 // FSOVERALL: all
diff --git a/clang/test/Driver/emit-flang-attrs.f90 b/clang/test/Driver/emit-flang-attrs.f90
new file mode 100644
index 000000000000..df23a8aa6e87
--- /dev/null
+++ b/clang/test/Driver/emit-flang-attrs.f90
@@ -0,0 +1,58 @@
+! REQUIRES: aarch64-registered-target
+! REQUIRES: classic_flang
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a -c %s 2>&1 | FileCheck --check-prefix=CHECK-ATTRS-NEON %s
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve -c %s 2>&1 | FileCheck --check-prefix=CHECK-ATTRS-SVE %s
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+nosve -c %s 2>&1 | FileCheck --check-prefix=CHECK-ATTRS-NOSVE %s
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve+nosve -c %s 2>&1 | FileCheck --check-prefix=CHECK-ATTRS-NOSVE %s
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve2+nosve2 -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-REVERT
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve2-aes -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-AES
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve2-sm4 -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-SM4
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve2-sha3 -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-SHA3
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve2-bitperm+nosve2-bitperm -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-BITPERM-REVERT
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve2 -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-IMPLY
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+nosve+sve2 -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-CONFLICT-REV
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve+sve2 -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE-SVE2
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve2-bitperm -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-BITPERM
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+nosve+sve2-aes -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE-SUBFEATURE-CONFLICT-REV
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve2-sm4+nosve2 -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-SUBFEATURE-CONFLICT
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve2-bitperm+nosve2-aes -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-SUBFEATURE-MIX
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve2-sm4+nosve2-sm4 -c %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-SM4-REVERT
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve2-sha3+nosve2-sha3 %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-SHA3-REVERT
+! RUN: %flang -### -target aarch64-linux-gnu -march=armv8-a+sve2-aes+nosve2-aes %s 2>&1 | FileCheck %s --check-prefix=CHECK-SVE2-AES-REVERT
+
+! CHECK-ATTRS-NEON: "{{.*}}flang2"
+! CHECK-ATTRS-NEON-SAME: "-target_features" "+neon,+v8a"
+! CHECK-ATTRS-SVE: "{{.*}}flang2"
+! CHECK-ATTRS-SVE-SAME: "-target_features" "+neon,+v8a,+sve"
+! CHECK-ATTRS-NOSVE: "{{.*}}flang2"
+! CHECK-ATTRS-NOSVE-SAME: "-target_features" "+neon,+v8a,-sve,-sve2,-sve2-bitperm,-sve2-sha3,-sve2-aes,-sve2-sm4"
+! CHECK-SVE2-REVERT: "{{.*}}flang2"
+! CHECK-SVE2-REVERT-SAME: "-target_features" "+neon,+v8a,+sve,-sve2,-sve2-bitperm,-sve2-sha3,-sve2-aes,-sve2-sm4"
+! CHECK-SVE2-AES:  "{{.*}}flang2"
+! CHECK-SVE2-AES-SAME: "-target_features" "+neon,+v8a,+sve2-aes,+sve,+sve2"
+! CHECK-SVE2-SM4: "{{.*}}flang2"
+! CHECK-SVE2-SM4-SAME: "-target_features" "+neon,+v8a,+sve2-sm4,+sve,+sve2"
+! CHECK-SVE2-SHA3: "{{.*}}flang2"
+! CHECK-SVE2-SHA3-SAME: "-target_features" "+neon,+v8a,+sve2-sha3,+sve,+sve2"
+! CHECK-SVE2-BITPERM-REVERT: "{{.*}}flang2"
+! CHECK-SVE2-BITPERM-REVERT-SAME: "-target_features" "+neon,+v8a,+sve,+sve2,-sve2-bitperm"
+! CHECK-SVE2-IMPLY: "{{.*}}flang2"
+! CHECK-SVE2-IMPLY-SAME: "-target_features" "+neon,+v8a,+sve2,+sve"
+! CHECK-SVE2-CONFLICT-REV: "{{.*}}flang2"
+! CHECK-SVE2-CONFLICT-REV-SAME: "-target_features" "+neon,+v8a,-sve2-bitperm,-sve2-sha3,-sve2-aes,-sve2-sm4,+sve2,+sve"
+! CHECK-SVE-SVE2: "{{.*}}flang2"
+! CHECK-SVE-SVE2-SAME: "-target_features" "+neon,+v8a,+sve2,+sve"
+! CHECK-SVE2-BITPERM: "{{.*}}flang2"
+! CHECK-SVE2-BITPERM-SAME: "-target_features" "+neon,+v8a,+sve2-bitperm,+sve,+sve2"
+! CHECK-SVE-SUBFEATURE-CONFLICT-REV: "{{.*}}flang2"
+! CHECK-SVE-SUBFEATURE-CONFLICT-REV-SAME: "-target_features" "+neon,+v8a,-sve2-bitperm,-sve2-sha3,-sve2-sm4,+sve2-aes,+sve,+sve2"
+! CHECK-SVE2-SUBFEATURE-CONFLICT:  "{{.*}}flang2"
+! CHECK-SVE2-SUBFEATURE-CONFLICT-SAME: "-target_features" "+neon,+v8a,+sve,-sve2,-sve2-bitperm,-sve2-sha3,-sve2-aes,-sve2-sm4"
+! CHECK-SVE2-SUBFEATURE-MIX: "{{.*}}flang2"
+! CHECK-SVE2-SUBFEATURE-MIX-SAME: "-target_features" "+neon,+v8a,+sve2-bitperm,+sve,+sve2,-sve2-aes"
+! CHECK-SVE2-SM4-REVERT: "{{.*}}flang2"
+! CHECK-SVE2-SM4-REVERT-SAME: "-target_features" "+neon,+v8a,+sve,+sve2,-sve2-sm4"
+! CHECK-SVE2-SHA3-REVERT: "{{.*}}flang2"
+! CHECK-SVE2-SHA3-REVERT-SAME: "-target_features" "+neon,+v8a,+sve,+sve2,-sve2-sha3"
+! CHECK-SVE2-AES-REVERT: "{{.*}}flang2"
+! CHECK-SVE2-AES-REVERT-SAME: "-target_features" "+neon,+v8a,+sve,+sve2,-sve2-aes"
diff --git a/clang/test/Driver/flang/Inputs/llvm-ir-input.ll b/clang/test/Driver/flang/Inputs/llvm-ir-input.ll
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/clang/test/Driver/flang/classic-flang-emit-flang-llvm.f95 b/clang/test/Driver/flang/classic-flang-emit-flang-llvm.f95
new file mode 100644
index 000000000000..225207c85db7
--- /dev/null
+++ b/clang/test/Driver/flang/classic-flang-emit-flang-llvm.f95
@@ -0,0 +1,10 @@
+! REQUIRES: classic_flang
+
+! Check that the -emit-flang-llvm option dumps LLVM IR pre-optimisation
+
+! RUN: %clang --driver-mode=flang -emit-flang-llvm -S -o %t.ll %s -### 2>&1 \
+! RUN:   | FileCheck %s
+! CHECK-NOT: argument unused during compilation: '-S'
+! CHECK: "{{.*}}flang1"
+! CHECK-NEXT: "{{.*}}flang2"
+! CHECK-NOT: "{{.*}}clang{{.*}}" "-cc1"
diff --git a/clang/test/Driver/flang/classic-flang-fp-contract.f95 b/clang/test/Driver/flang/classic-flang-fp-contract.f95
new file mode 100644
index 000000000000..b181065d1cac
--- /dev/null
+++ b/clang/test/Driver/flang/classic-flang-fp-contract.f95
@@ -0,0 +1,27 @@
+! REQUIRES: classic_flang
+
+! RUN: %flang -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT-ABSENCE
+! RUN: %flang -O1 -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT
+! RUN: %flang -O2 -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT
+! RUN: %flang -O3 -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT
+! RUN: %flang -Ofast -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT
+! RUN: %flang -ffp-contract=fast -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT-ABSENCE
+! RUN: %flang -O1 -ffp-contract=fast -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT
+! RUN: %flang -O2 -ffp-contract=fast -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT
+! RUN: %flang -O3 -ffp-contract=fast -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT
+! RUN: %flang -Ofast -ffp-contract=fast -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT
+! RUN: %flang -ffp-contract=on -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT-ABSENCE
+! RUN: %flang -O1 -ffp-contract=on -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT
+! RUN: %flang -O2 -ffp-contract=on -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT
+! RUN: %flang -O3 -ffp-contract=on -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT
+! RUN: %flang -Ofast -ffp-contract=on -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT
+! RUN: %flang -ffp-contract=off -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT-ABSENCE
+! RUN: %flang -O1 -ffp-contract=off -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT-ABSENCE
+! RUN: %flang -O2 -ffp-contract=off -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT-ABSENCE
+! RUN: %flang -O3 -ffp-contract=off -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT-ABSENCE
+! RUN: %flang -Ofast -ffp-contract=off -c %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-FLANG2-FP-CONTRACT-ABSENCE
+
+! CHECK-FLANG2-FP-CONTRACT: "{{.*}}flang2"
+! CHECK-FLANG2-FP-CONTRACT-SAME: "-x" "172" "0x40000000" "-x" "179" "1" "-x" "216" "0x1000"
+! CHECK-FLANG2-FP-CONTRACT-ABSENCE: "{{.*}}flang2"
+! CHECK-FLANG2-FP-CONTRACT-ABSENCE-SAME: "-x" "171" "0x40000000" "-x" "178" "1"
diff --git a/clang/test/Driver/flang/classic-flang-must-preprocess.F b/clang/test/Driver/flang/classic-flang-must-preprocess.F
new file mode 100644
index 000000000000..d52c1cf8d3c0
--- /dev/null
+++ b/clang/test/Driver/flang/classic-flang-must-preprocess.F
@@ -0,0 +1,12 @@
+! REQUIRES: classic_flang
+
+! Check that the driver invokes flang1 correctly for fixed-form Fortran code
+! which requires preprocessing.
+
+! RUN: %clang --driver-mode=flang -target x86_64-unknown-linux-gnu -c %s -### 2>&1 \
+! RUN:   | FileCheck %s
+! CHECK: "flang1"
+! CHECK-SAME: "-preprocess"
+! CHECK-SAME: "-nofreeform"
+! CHECK-NEXT: "flang2"
+! CHECK-NEXT: {{clang.* "-cc1"}}
diff --git a/clang/test/Driver/flang/classic-flang-must-preprocess.F95 b/clang/test/Driver/flang/classic-flang-must-preprocess.F95
new file mode 100644
index 000000000000..7d452a535784
--- /dev/null
+++ b/clang/test/Driver/flang/classic-flang-must-preprocess.F95
@@ -0,0 +1,12 @@
+! REQUIRES: classic_flang
+
+! Check that the driver invokes flang1 correctly for free-form Fortran code
+! which requires preprocessing.
+
+! RUN: %clang --driver-mode=flang -target x86_64-unknown-linux-gnu -c %s -### 2>&1 \
+! RUN:   | FileCheck %s
+! CHECK: "flang1"
+! CHECK-SAME: "-preprocess"
+! CHECK-SAME: "-freeform"
+! CHECK-NEXT: "flang2"
+! CHECK-NEXT: {{clang.* "-cc1"}}
diff --git a/clang/test/Driver/flang/classic-flang-version.f b/clang/test/Driver/flang/classic-flang-version.f
new file mode 100644
index 000000000000..c2082d3af8b7
--- /dev/null
+++ b/clang/test/Driver/flang/classic-flang-version.f
@@ -0,0 +1,3 @@
+! REQUIRES: classic-flang
+! RUN: %flang --version | FileCheck %s
+! CHECK: flang version {{.*}} ({{.*}}flang-compiler/classic-flang-llvm-project.git {{.*}})
diff --git a/clang/test/Driver/flang/classic-flang-vscale-mbits.f95 b/clang/test/Driver/flang/classic-flang-vscale-mbits.f95
new file mode 100644
index 000000000000..f0ed43aa027a
--- /dev/null
+++ b/clang/test/Driver/flang/classic-flang-vscale-mbits.f95
@@ -0,0 +1,28 @@
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve -msve-vector-bits=128 %s 2>&1 | FileCheck -check-prefix=CHECK-SVE-128 %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve -msve-vector-bits=128+ %s 2>&1 | FileCheck -check-prefix=CHECK-SVE-128PLUS %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve -msve-vector-bits=256 %s 2>&1 | FileCheck -check-prefix=CHECK-SVE-256 %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve -msve-vector-bits=256+ %s 2>&1 | FileCheck -check-prefix=CHECK-SVE-256PLUS %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve2 -msve-vector-bits=512 %s 2>&1 | FileCheck -check-prefix=CHECK-SVE2-512 %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve2 -msve-vector-bits=512+ %s 2>&1 | FileCheck -check-prefix=CHECK-SVE2-512PLUS %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve2-sha3 -msve-vector-bits=2048 %s 2>&1 | FileCheck -check-prefix=CHECK-SVE2SHA3-2048 %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve2-sha3 -msve-vector-bits=2048+ %s 2>&1 | FileCheck -check-prefix=CHECK-SVE2SHA3-2048PLUS %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve2 -msve-vector-bits=scalable %s 2>&1 | FileCheck -check-prefix=CHECK-SVE2-SCALABLE %s
+
+// CHECK-SVE-128: "-target_features" "+neon,+v8a,+sve"
+// CHECK-SVE-128-DAG: "-vscale_range_min" "1" "-vscale_range_max" "1"
+// CHECK-SVE-128PLUS: "-target_features" "+neon,+v8a,+sve"
+// CHECK-SVE-128PLUS-DAG: "-vscale_range_min" "1" "-vscale_range_max" "0"
+// CHECK-SVE-256: "-target_features" "+neon,+v8a,+sve"
+// CHECK-SVE-256-DAG: "-vscale_range_min" "2" "-vscale_range_max" "2"
+// CHECK-SVE-256PLUS: "-target_features" "+neon,+v8a,+sve"
+// CHECK-SVE-256PLUS-DAG: "-vscale_range_min" "2" "-vscale_range_max" "0"
+// CHECK-SVE2-512: "-target_features" "+neon,+v8a,+sve2,+sve"
+// CHECK-SVE2-512-DAG: "-vscale_range_min" "4" "-vscale_range_max" "4"
+// CHECK-SVE2-512PLUS: "-target_features" "+neon,+v8a,+sve2,+sve"
+// CHECK-SVE2-512PLUS-DAG: "-vscale_range_min" "4" "-vscale_range_max" "0"
+// CHECK-SVE2SHA3-2048: "-target_features" "+neon,+v8a,+sve2-sha3,+sve,+sve2"
+// CHECK-SVE2SHA3-2048-DAG: "-vscale_range_min" "16" "-vscale_range_max" "16"
+// CHECK-SVE2SHA3-2048PLUS: "-target_features" "+neon,+v8a,+sve2-sha3,+sve,+sve2"
+// CHECK-SVE2SHA3-2048PLUS-DAG: "-vscale_range_min" "16" "-vscale_range_max" "0"
+// CHECK-SVE2-SCALABLE: "-target_features" "+neon,+v8a,+sve2,+sve"
+// CHECK-SVE2-SCALABLE-DAG: "-vscale_range_min" "1" "-vscale_range_max" "16"
diff --git a/clang/test/Driver/flang/classic-flang-vscale.f95 b/clang/test/Driver/flang/classic-flang-vscale.f95
new file mode 100644
index 000000000000..8110be594db5
--- /dev/null
+++ b/clang/test/Driver/flang/classic-flang-vscale.f95
@@ -0,0 +1,28 @@
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a %s 2>&1 | FileCheck -check-prefix=CHECK-NEON %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve %s 2>&1 | FileCheck -check-prefix=CHECK-SVE %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve2 %s 2>&1 | FileCheck -check-prefix=CHECK-SVE2 %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve2-sha3 %s 2>&1 | FileCheck -check-prefix=CHECK-SVE2SHA3 %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve+nosve %s 2>&1 | FileCheck -check-prefix=CHECK-SVE-NOSVE %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve2+nosve2-sha3 %s 2>&1 | FileCheck -check-prefix=CHECK-SVE2-NOSVE2SHA3 %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve2-sha3+nosve2 %s 2>&1 | FileCheck -check-prefix=CHECK-SVE2SHA3-NOSVE2 %s
+// RUN: %clang --driver-mode=flang -### -S --target=aarch64 -march=armv8-a+sve2-sha3+nosve %s 2>&1 | FileCheck -check-prefix=CHECK-SVE2SHA3-NOSVE %s
+
+// CHECK-NEON: "-target_features" "+neon,+v8a"
+// CHECK-NEON-NOT: "-vscale_range_min"
+// CHECK-NEON-NOT: "-vscale_range_max"
+// CHECK-SVE: "-target_features" "+neon,+v8a,+sve"
+// CHECK-SVE-DAG: "-vscale_range_min" "1" "-vscale_range_max" "16"
+// CHECK-SVE2: "-target_features" "+neon,+v8a,+sve2,+sve"
+// CHECK-SVE2-DAG: "-vscale_range_min" "1" "-vscale_range_max" "16"
+// CHECK-SVE2SHA3: "-target_features" "+neon,+v8a,+sve2-sha3,+sve,+sve2"
+// CHECK-SVE2SHA3-DAG: "-vscale_range_min" "1" "-vscale_range_max" "16"
+// CHECK-SVE-NOSVE: "-target_features" "+neon,+v8a,-sve,-sve2,-sve2-bitperm,-sve2-sha3,-sve2-aes,-sve2-sm4"
+// CHECK-SVE-NOSVE-NOT: "-vscale_range_min"
+// CHECK-SVE-NOSVE-NOT: "-vscale_range_max"
+// CHECK-SVE2-NOSVE2SHA3: "-target_features" "+neon,+v8a,+sve2,+sve,-sve2-sha3"
+// CHECK-SVE2-NOSVE2SHA3-DAG: "-vscale_range_min" "1" "-vscale_range_max" "16"
+// CHECK-SVE2SHA3-NOSVE2: "-target_features" "+neon,+v8a,+sve,-sve2,-sve2-bitperm,-sve2-sha3,-sve2-aes,-sve2-sm4"
+// CHECK-SVE2SHA3-NOSVE2-DAG: "-vscale_range_min" "1" "-vscale_range_max" "16"
+// CHECK-SVE2SHA3-NOSVE: "-target_features" "+neon,+v8a,-sve,-sve2,-sve2-bitperm,-sve2-sha3,-sve2-aes,-sve2-sm4"
+// CHECK-SVE2SHA3-NOSVE-NOT: "-vscale_range_min"
+// CHECK-SVE2SHA3-NOSVE-NOT: "-vscale_range_max"
diff --git a/clang/test/Driver/flang/classic-flang.f b/clang/test/Driver/flang/classic-flang.f
new file mode 100644
index 000000000000..98f74d9626d7
--- /dev/null
+++ b/clang/test/Driver/flang/classic-flang.f
@@ -0,0 +1,26 @@
+! REQUIRES: classic_flang
+
+! Check that the driver invokes flang1 correctly for preprocessed fixed-form
+! Fortran code.
+
+! RUN: %clang --driver-mode=flang -target x86_64-unknown-linux-gnu -c %s -### 2>&1 \
+! RUN:   | FileCheck %s
+! CHECK: "flang1"
+! CHECK-NOT: "-preprocess"
+! CHECK-SAME: "-nofreeform"
+! CHECK-NEXT: "flang2"
+! CHECK-NEXT: {{clang.* "-cc1"}}
+
+! Check that the driver invokes flang1 correctly when preprocessing is
+! explicitly requested.
+
+! RUN: %clang --driver-mode=flang -target x86_64-unknown-linux-gnu -E %s -### 2>&1 \
+! RUN:   | FileCheck --check-prefix=CHECK-PREPROCESS %s
+! CHECK-PREPROCESS: "flang1"
+! CHECK-PREPROCESS-SAME: "-preprocess"
+! CHECK-PREPROCESS-SAME: "-es"
+! CHECK-PREPROCESS-SAME: "-pp"
+! CHECK-PREPROCESS-NOT: "flang1"
+! CHECK-PREPROCESS-NOT: "flang2"
+! CHECK-PREPROCESS-NOT: {{clang.* "-cc1"}}
+! CHECK-PREPROCESS-NOT: {{clang.* "-cc1as"}}
diff --git a/clang/test/Driver/flang/classic-flang.f95 b/clang/test/Driver/flang/classic-flang.f95
new file mode 100644
index 000000000000..3350bd45550f
--- /dev/null
+++ b/clang/test/Driver/flang/classic-flang.f95
@@ -0,0 +1,120 @@
+! REQUIRES: classic_flang
+
+! Check that the driver invokes flang1 correctly for preprocessed free-form
+! Fortran code. Also check that the backend is invoked correctly.
+
+! RUN: %clang --driver-mode=flang -target x86_64-unknown-linux-gnu -c %s -### 2>&1 \
+! RUN:   | FileCheck --check-prefix=CHECK-OBJECT %s
+! CHECK-OBJECT: "flang1"
+! CHECK-OBJECT-NOT: "-preprocess"
+! CHECK-OBJECT-SAME: "-freeform"
+! CHECK-OBJECT-NEXT: "flang2"
+! CHECK-OBJECT-SAME: "-asm" [[LLFILE:.*.ll]]
+! CHECK-OBJECT-NEXT: {{clang.* "-cc1"}}
+! CHECK-OBJECT-SAME: "-o" "classic-flang.o"
+! CHECK-OBJECT-SAME: "-x" "ir"
+! CHECK-OBJECT-SAME: [[LLFILE]]
+
+! Check that the driver invokes flang1 correctly when preprocessing is
+! explicitly requested.
+
+! RUN: %clang --driver-mode=flang -target x86_64-unknown-linux-gnu -E %s -### 2>&1 \
+! RUN:   | FileCheck --check-prefix=CHECK-PREPROCESS %s
+! CHECK-PREPROCESS: "flang1"
+! CHECK-PREPROCESS-SAME: "-preprocess"
+! CHECK-PREPROCESS-SAME: "-es"
+! CHECK-PREPROCESS-SAME: "-pp"
+! CHECK-PREPROCESS-NOT: "flang1"
+! CHECK-PREPROCESS-NOT: "flang2"
+! CHECK-PREPROCESS-NOT: {{clang.* "-cc1"}}
+! CHECK-PREPROCESS-NOT: {{clang.* "-cc1as"}}
+
+! Check that the backend job (clang -cc1) is not combined into the compile job
+! (flang2) even if -integrated-as is specified.
+
+! RUN: %clang --driver-mode=flang -target x86_64-unknown-linux-gnu -integrated-as -S %s -### 2>&1 \
+! RUN:   | FileCheck --check-prefix=CHECK-ASM %s
+! CHECK-ASM: "flang1"
+! CHECK-ASM-NEXT: "flang2"
+! CHECK-ASM-SAME: "-asm" [[LLFILE:.*.ll]]
+! CHECK-ASM-NEXT: {{clang.* "-cc1"}}
+! CHECK-ASM-SAME: "-o" "classic-flang.s"
+! CHECK-ASM-SAME: "-x" "ir"
+! CHECK-ASM-SAME: [[LLFILE]]
+
+! Check that the linker job is given the correct libraries and library paths.
+
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -mp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-MAIN,CHECK-DYNAMIC-FLANG,CHECK-DYNAMIC-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -mp -nomp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-MAIN,CHECK-DYNAMIC-FLANG,CHECK-NO-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -fopenmp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-MAIN,CHECK-DYNAMIC-FLANG,CHECK-DYNAMIC-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -fopenmp -fno-openmp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-MAIN,CHECK-DYNAMIC-FLANG,CHECK-NO-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -fopenmp -static-openmp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-MAIN,CHECK-DYNAMIC-FLANG,CHECK-STATIC-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -fopenmp -static-flang-libs \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-MAIN,CHECK-STATIC-FLANG,CHECK-DYNAMIC-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -static-flang-libs \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-MAIN,CHECK-STATIC-FLANG,CHECK-NO-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -Mnomain \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-NOMAIN,CHECK-DYNAMIC-FLANG %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -fno-fortran-main \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-NOMAIN,CHECK-DYNAMIC-FLANG %s
+! CHECK-LD:                "{{.*}}ld{{(.exe)?}}"
+! CHECK-LD-NOT:            "-static"
+! CHECK-LD-SAME:           "{{[^"]*}}classic-flang-{{[^ ]*}}.o"
+! CHECK-MAIN-SAME:         "-lflangmain"
+! CHECK-NOMAIN-NOT:        "-lflangmain"
+! CHECK-LD-SAME:           "-lfoo" "-L{{[^ ]*[/\\]+}}basic_linux_tree{{[/\\]+}}usr{{[/\\]+}}lib"
+! CHECK-DYNAMIC-FLANG-NOT: "-Bstatic"
+! CHECK-DYNAMIC-FLANG:     "-lflang" "-lflangrti" "-lpgmath" "-lpthread" "-lrt" "-lm"
+! CHECK-DYNAMIC-FLANG-NOT: "-Bdynamic"
+! CHECK-STATIC-FLANG:      "-Bstatic" "-lflang" "-lflangrti" "-lpgmath" "-Bdynamic" "-lpthread" "-lrt" "-lm"
+! CHECK-DYNAMIC-OMP-NOT:   "-Bstatic"
+! CHECK-DYNAMIC-OMP:       "-lomp" "-L{{[^ ]*[/\\]+}}basic_linux_tree{{[/\\]+}}usr{{[/\\]+}}lib"
+! CHECK-DYNAMIC-OMP-NOT:   "-Bdynamic"
+! CHECK-STATIC-OMP:        "-Bstatic" "-lomp" "-Bdynamic" "-L{{[^ ]*[/\\]+}}basic_linux_tree{{[/\\]+}}usr{{[/\\]+}}lib"
+! CHECK-NO-OMP-NOT:        "-lomp"
+
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -static -static-flang-libs \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD-STATIC,CHECK-NO-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -static -fopenmp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD-STATIC,CHECK-STATIC-BOTH %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -static -fopenmp -static-openmp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD-STATIC,CHECK-STATIC-BOTH %s
+! CHECK-LD-STATIC:     "{{.*}}ld{{(.exe)?}}"
+! CHECK-LD-STATIC:     "-static" "-o" "a.out"
+! CHECK-LD-STATIC:     "{{[^"]*}}classic-flang-{{[^ ]*}}.o" "-lflangmain" "-lfoo" "-L{{[^ ]*[/\\]+}}basic_linux_tree{{[/\\]+}}usr{{[/\\]+}}lib"
+! CHECK-LD-STATIC-NOT: "-Bstatic"
+! CHECK-LD-STATIC:     "-lflang" "-lflangrti" "-lpgmath" "-lpthread" "-lrt" "-lm"
+! CHECK-LD-STATIC-NOT: "-Bdynamic"
+! CHECK-STATIC-BOTH-NOT: "-Bstatic"
+! CHECK-STATIC-BOTH:     "-lomp"
+! CHECK-STATIC-BOTH-NOT: "-Bdynamic"
+
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -no-flang-libs \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-NOFLANGLIBS %s
+! CHECK-NOFLANGLIBS:      "{{.*}}ld{{(.exe)?}}"
+! CHECK-NOFLANGLIBS-SAME: "{{[^"]*}}classic-flang-{{[^ ]*}}.o"
+! CHECK-NOFLANGLIBS-NOT:  "-lflangmain"
+! CHECK-NOFLANGLIBS-SAME: "-lfoo" "-L{{[^ ]*[/\\]+}}basic_linux_tree{{[/\\]+}}usr{{[/\\]+}}lib"
+! CHECK-NOFLANGLIBS-NOT:  "-lflang" "-lflangrti" "-lpgmath"
+! CHECK-NOFLANGLIBS:      "-lm" "-lgcc"
+! CHECK-NOFLANGLIBS:      "-lgcc_s"
+! CHECK-NOFLANGLIBS:      "-lc"
+
+! In Flang mode, we always link with libm, even with -nostdlib.
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -nostdlib \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-NOSTDLIB %s
+! CHECK-NOSTDLIB:      "{{.*}}ld{{(.exe)?}}"
+! CHECK-NOSTDLIB-SAME: "{{[^"]*}}classic-flang-{{[^ ]*}}.o"
+! CHECK-NOSTDLIB-NOT:  "-lflangmain"
+! CHECK-NOSTDLIB-SAME: "-lfoo" "-L{{[^ ]*[/\\]+}}basic_linux_tree{{[/\\]+}}usr{{[/\\]+}}lib"
+! CHECK-NOSTDLIB-NOT:  "-lflang" "-lflangrti" "-lpgmath"
+! CHECK-NOSTDLIB-NOT:  "-lpthread" "-lrt"
+! CHECK-NOSTDLIB:      "-lm"
+! CHECK-NOSTDLIB-NOT:  "-lgcc"
+! CHECK-NOSTDLIB-NOT:  "-lgcc_s"
+! CHECK-NOSTDLIB-NOT:  "-lc"
diff --git a/clang/test/Driver/flang/flang.f90 b/clang/test/Driver/flang/flang.f90
index 5d8edf6308b0..8caa45f6342c 100644
--- a/clang/test/Driver/flang/flang.f90
+++ b/clang/test/Driver/flang/flang.f90
@@ -1,5 +1,7 @@
 ! Check that flang -fc1 is invoked when in --driver-mode=flang.
 
+! UNSUPPORTED: classic_flang
+
 ! This is a copy of flang_ucase.F90 because the driver has logic in it which
 ! differentiates between F90 and f90 files. Flang will not treat these files
 ! differently.
diff --git a/clang/test/Driver/flang/flang_ucase.F90 b/clang/test/Driver/flang/flang_ucase.F90
index 50305ee337e1..21f7c469144b 100644
--- a/clang/test/Driver/flang/flang_ucase.F90
+++ b/clang/test/Driver/flang/flang_ucase.F90
@@ -1,5 +1,7 @@
 ! Check that flang -fc1 is invoked when in --driver-mode=flang.
 
+! UNSUPPORTED: classic_flang
+
 ! This is a copy of flang.f90 because the driver has logic in it which
 ! differentiates between F90 and f90 files. Flang will not treat these files
 ! differently.
diff --git a/clang/test/Driver/flang/llvm-ir-input.f b/clang/test/Driver/flang/llvm-ir-input.f
new file mode 100644
index 000000000000..c34bf28328cb
--- /dev/null
+++ b/clang/test/Driver/flang/llvm-ir-input.f
@@ -0,0 +1,7 @@
+! Check that LLVM IR input is passed to clang instead of flang1.
+
+! REQUIRES: classic_flang
+! RUN: %clang --driver-mode=flang -S %S/Inputs/llvm-ir-input.ll -### 2>&1 | FileCheck %s
+
+! CHECK-NOT: flang1
+! CHECK: "{{.*}}clang{{.*}}" "-cc1"
diff --git a/clang/test/Driver/flang/multiple-inputs-mixed.f90 b/clang/test/Driver/flang/multiple-inputs-mixed.f90
index 2395dbecf1fe..8f3918f7cb21 100644
--- a/clang/test/Driver/flang/multiple-inputs-mixed.f90
+++ b/clang/test/Driver/flang/multiple-inputs-mixed.f90
@@ -1,5 +1,7 @@
 ! Check that flang can handle mixed C and fortran inputs.
 
+! UNSUPPORTED: classic_flang
+
 ! RUN: %clang --driver-mode=flang -### -fsyntax-only %S/Inputs/one.f90 %S/Inputs/other.c 2>&1 | FileCheck --check-prefixes=CHECK-SYNTAX-ONLY %s
 ! CHECK-SYNTAX-ONLY-LABEL: "{{[^"]*}}flang-new{{[^"/]*}}" "-fc1"
 ! CHECK-SYNTAX-ONLY: "{{[^"]*}}/Inputs/one.f90"
diff --git a/clang/test/Driver/flang/multiple-inputs.f90 b/clang/test/Driver/flang/multiple-inputs.f90
index ada999e927a6..4068ac3a0966 100644
--- a/clang/test/Driver/flang/multiple-inputs.f90
+++ b/clang/test/Driver/flang/multiple-inputs.f90
@@ -1,5 +1,7 @@
 ! Check that flang driver can handle multiple inputs at once.
 
+! UNSUPPORTED: classic_flang
+
 ! RUN: %clang --driver-mode=flang -### -fsyntax-only %S/Inputs/one.f90 %S/Inputs/two.f90 2>&1 | FileCheck --check-prefixes=CHECK-SYNTAX-ONLY %s
 ! CHECK-SYNTAX-ONLY-LABEL: "{{[^"]*}}flang-new{{[^"/]*}}" "-fc1"
 ! CHECK-SYNTAX-ONLY: "{{[^"]*}}/Inputs/one.f90"
diff --git a/clang/test/Driver/flang/reassoc.f90 b/clang/test/Driver/flang/reassoc.f90
new file mode 100644
index 000000000000..fe42087f7070
--- /dev/null
+++ b/clang/test/Driver/flang/reassoc.f90
@@ -0,0 +1,59 @@
+! REQUIRES: classic_flang
+
+! Tests for flags which generate nsw, reassoc attributes
+
+! RUN: %flang -Kieee %s -### 2>&1 | FileCheck --check-prefixes=IEEE,NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -Knoieee %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -ffast-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fno-fast-math %s -### 2>&1 | FileCheck --check-prefixes=NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -frelaxed-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fassociative-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,NO_RELAXED,REASSOC_NSZ %s
+! RUN: %flang -fno-associative-math %s -### 2>&1 | FileCheck --check-prefixes=NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fsigned-zeros %s -### 2>&1 | FileCheck --check-prefixes=NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fno-signed-zeros %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,NO_RELAXED,NO_REASSOC,NSZ %s
+
+! RUN: %flang -fno-associative-math -fno-signed-zeros %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,NO_RELAXED,NO_REASSOC,NSZ %s
+! RUN: %flang -fno-associative-math -fsigned-zeros %s -### 2>&1 | FileCheck --check-prefixes=NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fassociative-math -fno-signed-zeros %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,NO_RELAXED,REASSOC_NSZ %s
+! RUN: %flang -fassociative-math -fsigned-zeros %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+
+! RUN: %flang -Kieee -fassociative-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,NO_RELAXED,REASSOC_NSZ %s
+! RUN: %flang -Kieee -fno-associative-math %s -### 2>&1 | FileCheck --check-prefixes=IEEE,NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -Kieee -fsigned-zeros %s -### 2>&1 | FileCheck --check-prefixes=IEEE,NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -Kieee -fno-signed-zeros %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,NO_RELAXED,NO_REASSOC,NSZ %s
+! RUN: %flang -ffast-math -fassociative-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_RELAXED,REASSOC_NSZ %s
+! RUN: %flang -ffast-math -fno-associative-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -ffast-math -fsigned-zeros %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -ffast-math -fno-signed-zeros %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_RELAXED,NO_REASSOC,NSZ %s
+! RUN: %flang -frelaxed-math -fassociative-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,REASSOC_NSZ %s
+! RUN: %flang -frelaxed-math -fno-associative-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -frelaxed-math -fsigned-zeros %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -frelaxed-math -fno-signed-zeros %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,NO_REASSOC,NSZ %s
+
+! RUN: %flang -fassociative-math -Kieee %s -### 2>&1 | FileCheck --check-prefixes=IEEE,NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fno-associative-math -Kieee %s -### 2>&1 | FileCheck --check-prefixes=IEEE,NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fsigned-zeros -Kieee %s -### 2>&1 | FileCheck --check-prefixes=IEEE,NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fno-signed-zeros -Kieee %s -### 2>&1 | FileCheck --check-prefixes=IEEE,NO_FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fassociative-math -ffast-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_RELAXED,REASSOC_NSZ %s
+! RUN: %flang -fno-associative-math -ffast-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fsigned-zeros -ffast-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,FAST,NO_RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fno-signed-zeros -ffast-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_RELAXED,NO_REASSOC,NSZ %s
+! RUN: %flang -fassociative-math -frelaxed-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,REASSOC_NSZ %s
+! RUN: %flang -fno-associative-math -frelaxed-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fsigned-zeros -frelaxed-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,RELAXED,NO_REASSOC,NO_NSZ %s
+! RUN: %flang -fno-signed-zeros -frelaxed-math %s -### 2>&1 | FileCheck --check-prefixes=NO_IEEE,NO_FAST,NO_REASSOC,NSZ %s
+
+! IEEE: {{.*}}flang2{{.*}} "-ieee" "1"
+! NO_IEEE-NOT: {{.*}}flang2{{.*}} "-ieee" "1"
+
+! FAST: {{.*}}flang2{{.*}} "-x" "216" "1"
+! NO_FAST-NOT: {{.*}}flang2{{.*}} "-x" "216" "1"
+
+! RELAXED: {{.*}}flang2{{.*}} "-x" "15" "0x400"
+! NO_RELAXED-NOT: {{.*}}flang2{{.*}} "-x" "15" "0x400"
+
+! REASSOC_NSZ: {{.*}}flang2{{.*}} "-x" "216" "0x8" "-x" "216" "0x10"
+! NO_REASSOC-NOT: {{.*}}flang2{{.*}} "-x" "216" "0x10"
+
+! NSZ: {{.*}}flang2{{.*}} "-x" "216" "0x8"
+! NO_NSZ-NOT: {{.*}}flang2{{.*}} "-x" "216" "0x8"
diff --git a/clang/test/Driver/fortran-phases.f90 b/clang/test/Driver/fortran-phases.f90
new file mode 100644
index 000000000000..57d5f2c92b78
--- /dev/null
+++ b/clang/test/Driver/fortran-phases.f90
@@ -0,0 +1,119 @@
+! Test to see that the correct phases are run for the commandline input
+
+! REQUIRES: classic_flang
+
+! RUN: %flang -ccc-print-phases 2>&1 %s | FileCheck %s --check-prefix=LINK-NOPP
+! RUN: %flang -ccc-print-phases -c 2>&1 %s | FileCheck %s --check-prefix=CONLY-NOPP
+! RUN: %flang -ccc-print-phases -S 2>&1 %s | FileCheck %s --check-prefix=AONLY-NOPP
+! RUN: %flang -ccc-print-phases -c -emit-llvm 2>&1 %s | FileCheck %s --check-prefix=LLONLY-NOPP
+! RUN: %flang -ccc-print-phases -S -emit-llvm 2>&1 %s | FileCheck %s --check-prefix=LLONLY-NOPP
+! RUN: %flang -ccc-print-phases -emit-flang-llvm 2>&1 %s | FileCheck %s --check-prefix=FLLONLY-NOPP
+! RUN: %flang -ccc-print-phases -fsyntax-only 2>&1 %s | FileCheck %s --check-prefix=SONLY-NOPP
+! RUN: %flang -ccc-print-phases -E 2>&1 %s | FileCheck %s --check-prefix=PPONLY-NOPP
+
+! RUN: %flang -ccc-print-phases 2>&1 -x f95-cpp-input %s | FileCheck %s --check-prefix=LINK
+! RUN: %flang -ccc-print-phases 2>&1 -x f95-cpp-input %s | FileCheck %s --check-prefix=LINK
+! RUN: %flang -ccc-print-phases -c 2>&1 -x f95-cpp-input %s | FileCheck %s --check-prefix=CONLY
+! RUN: %flang -ccc-print-phases -S 2>&1 -x f95-cpp-input %s | FileCheck %s --check-prefix=AONLY
+! RUN: %flang -ccc-print-phases -c -emit-llvm 2>&1 -x f95-cpp-input %s | FileCheck %s --check-prefix=LLONLY
+! RUN: %flang -ccc-print-phases -S -emit-llvm 2>&1 -x f95-cpp-input %s | FileCheck %s --check-prefix=LLONLY
+! RUN: %flang -ccc-print-phases -emit-flang-llvm 2>&1 -x f95-cpp-input %s | FileCheck %s --check-prefix=FLLONLY
+! RUN: %flang -ccc-print-phases -fsyntax-only 2>&1 -x f95-cpp-input %s | FileCheck %s --check-prefix=SONLY
+! RUN: %flang -ccc-print-phases -E 2>&1 -x f95-cpp-input %s | FileCheck %s --check-prefix=PPONLY
+
+! LINK-NOPP: 0: input, {{.*}}, f95
+! LINK-NOPP: 1: compiler, {0}, ir
+! LINK-NOPP: 2: backend, {1}, assembler
+! LINK-NOPP: 3: assembler, {2}, object
+! LINK-NOPP: 4: linker, {3}, image
+
+! CONLY-NOPP: 0: input, {{.*}}, f95
+! CONLY-NOPP: 1: compiler, {0}, ir
+! CONLY-NOPP: 2: backend, {1}, assembler
+! CONLY-NOPP: 3: assembler, {2}, object
+! CONLY-NOPP-NOT: {{.*}}: linker, {{{.*}}}, image
+
+! AONLY-NOPP: 0: input, {{.*}}, f95
+! AONLY-NOPP: 1: compiler, {0}, ir
+! AONLY-NOPP: 2: backend, {1}, assembler
+! AONLY-NOPP-NOT: {{.*}}: assembler, {{{.*}}}, object
+! AONLY-NOPP-NOT: {{.*}}: linker, {{{.*}}}, image
+
+! LLONLY-NOPP: 0: input, {{.*}}, f95
+! LLONLY-NOPP: 1: compiler, {0}, ir
+! LLONLY-NOPP-NOT: {{.*}}: backend, {{{.*}}}, assembler
+! LLONLY-NOPP-NOT: {{.*}}: assembler, {{{.*}}}, object
+! LLONLY-NOPP-NOT: {{.*}}: linker, {{{.*}}}, image
+
+! FLLONLY-NOPP: 0: input, {{.*}}, f95
+! FLLONLY-NOPP: 1: compiler, {0}, ir
+! FLLONLY-NOPP-NOT: {{.*}}: backend, {{{.*}}}, assembler
+! FLLONLY-NOPP-NOT: {{.*}}: assembler, {{{.*}}}, object
+! FLLONLY-NOPP-NOT: {{.*}}: linker, {{{.*}}}, image
+
+! SONLY-NOPP: 0: input, {{.*}}, f95
+! SONLY-NOPP-NOT: {{.*}}: compiler, {{{.*}}}, ir
+! SONLY-NOPP-NOT: {{.*}}: backend, {{{.*}}}, assembler
+! SONLY-NOPP-NOT: {{.*}}: assembler, {{{.*}}}, object
+! SONLY-NOPP-NOT: {{.*}}: linker, {{{.*}}}, image
+
+! flang always preprocesses with -E regardless of file extension
+! PPONLY-NOPP: 0: input, {{.*}}, f95
+! PPONLY-NOPP: 1: preprocessor, {0}, f95
+! PPONLY-NOPP-NOT: {{.*}}: compiler, {{{.*}}}, ir
+! PPONLY-NOPP-NOT: {{.*}}: backend, {{{.*}}}, assembler
+! PPONLY-NOPP-NOT: {{.*}}: assembler, {{{.*}}}, object
+! PPONLY-NOPP-NOT: {{.*}}: linker, {{{.*}}}, image
+
+! LINK: 0: input, {{.*}}, f95-cpp-input
+! LINK: 1: preprocessor, {0}, f95
+! LINK: 2: compiler, {1}, ir
+! LINK: 3: backend, {2}, assembler
+! LINK: 4: assembler, {3}, object
+! LINK: 5: linker, {4}, image
+
+! CONLY: 0: input, {{.*}}, f95-cpp-input
+! CONLY: 1: preprocessor, {0}, f95
+! CONLY: 2: compiler, {1}, ir
+! CONLY: 3: backend, {2}, assembler
+! CONLY: 4: assembler, {3}, object
+! CONLY-NOT: {{.*}}: linker, {{{.*}}}, image
+
+! AONLY: 0: input, {{.*}}, f95-cpp-input
+! AONLY: 1: preprocessor, {0}, f95
+! AONLY: 2: compiler, {1}, ir
+! AONLY: 3: backend, {2}, assembler
+! AONLY-NOT: {{.*}}: assembler, {{{.*}}}, object
+! AONLY-NOT: {{.*}}: linker, {{{.*}}}, image
+
+! LLONLY: 0: input, {{.*}}, f95-cpp-input
+! LLONLY: 1: preprocessor, {0}, f95
+! LLONLY: 2: compiler, {1}, ir
+! LLONLY-NOT: {{.*}}: backend, {{{.*}}}, assembler
+! LLONLY-NOT: {{.*}}: assembler, {{{.*}}}, object
+! LLONLY-NOT: {{.*}}: linker, {{{.*}}}, image
+
+! FLLONLY: 0: input, {{.*}}, f95-cpp-input
+! FLLONLY: 1: preprocessor, {0}, f95
+! FLLONLY: 2: compiler, {1}, ir
+! FLLONLY-NOT: {{.*}}: backend, {{{.*}}}, assembler
+! FLLONLY-NOT: {{.*}}: assembler, {{{.*}}}, object
+! FLLONLY-NOT: {{.*}}: linker, {{{.*}}}, image
+
+! SONLY: 0: input, {{.*}}, f95-cpp-input
+! SONLY: 1: preprocessor, {0}, f95
+! SONLY-NOT: {{.*}}: compiler, {{{.*}}}, ir
+! SONLY-NOT: {{.*}}: backend, {{{.*}}}, assembler
+! SONLY-NOT: {{.*}}: assembler, {{{.*}}}, object
+! SONLY-NOT: {{.*}}: linker, {{{.*}}}, image
+
+! PPONLY: 0: input, {{.*}}, f95-cpp-input
+! PPONLY: 1: preprocessor, {0}, f95
+! PPONLY-NOT: {{.*}}: compiler, {{{.*}}}, ir
+! PPONLY-NOT: {{.*}}: backend, {{{.*}}}, assembler
+! PPONLY-NOT: {{.*}}: assembler, {{{.*}}}, object
+! PPONLY-NOT: {{.*}}: linker, {{{.*}}}, image
+
+program hello
+  write(*, *) "Hello"
+end program hello
diff --git a/clang/test/Driver/fortran-preprocessor.f90 b/clang/test/Driver/fortran-preprocessor.f90
new file mode 100644
index 000000000000..d9e5620145ac
--- /dev/null
+++ b/clang/test/Driver/fortran-preprocessor.f90
@@ -0,0 +1,48 @@
+! REQUIRES: classic_flang
+
+! -cpp should preprocess as it goes, regardless of input file extension
+! RUN: %flang -cpp -c -DHELLO="hello all" -### %s 2>&1 | FileCheck %s --check-prefixes=ALL,CPP,PP
+! RUN: %flang -cpp -c -DHELLO="hello all" -### -x f95-cpp-input %s 2>&1 | FileCheck %s --check-prefixes=ALL,CPP,PP
+! -E should preprocess then stop, regardless of input file extension
+! RUN: %flang -E -DHELLO="hello all" -### %s 2>&1 | FileCheck %s --check-prefixes=ALL,E,PPONLY
+! RUN: %flang -E -DHELLO="hello all" -### -x f95-cpp-input %s 2>&1 | FileCheck %s --check-prefixes=ALL,E,PPONLY
+! -cpp and -E are redundant
+! RUN: %flang -E -cpp -DHELLO="hello all" -### %s 2>&1 | FileCheck %s --check-prefixes=ALL,E,PPONLY
+
+! Don't link when given linker input
+! RUN: %flang -E -cpp -Wl,-rpath=blah -### %s 2>&1 | FileCheck %s --check-prefixes=ALL,E,PPONLY
+
+! Explicitly test this nonsence case causing a bug with LLVM 13/14
+! RUN: %flang -E -traditional-cpp -DHELLO="hello all" -x f95-cpp-input -### %s 2>&1 | FileCheck %s --check-prefixes=ALL,E,PPONLY
+
+! Test -save-temps does not break things (same codepath as -traditional-cpp bug above)
+! RUN: %flang -E -DHELLO="hello all" -save-temps -### %s 2>&1 | FileCheck %s --check-prefixes=ALL,E,PPONLY
+! RUN: %flang -E -DHELLO="hello all" -save-temps -### -x f95-cpp-input %s 2>&1 | FileCheck %s --check-prefixes=ALL,E,PPONLY
+! RUN: %flang -cpp -c -DHELLO="hello all" -save-temps -### %s 2>&1 | FileCheck %s --check-prefixes=ALL,CPP,PP
+! RUN: %flang -cpp -c -DHELLO="hello all" -save-temps -### -x f95-cpp-input %s 2>&1 | FileCheck %s --check-prefixes=ALL,CPP,PP
+
+! Test for the correct cmdline flags
+! Consume up to flang1 line
+! ALL-LABEL: "{{.*}}flang1"
+! CPP-NOT: "-es"
+! CPP: "-preprocess"
+! CPP-NOT: "-es"
+
+! E-DAG: "-es"
+! E-DAG: "-preprocess"
+
+! CPP should continue to build object
+! PP: "{{.*}}flang2"
+! PPONLY-NOT: "{{.*}}flang2"
+
+! flang1 and flang2 should only be called at most once!
+! ALL-NOT: "{{.*}}flang1"
+! ALL-NOT: "{{.*}}flang2"
+
+! These commands should never call a linker!
+! ALL-NOT: "{{.*}}ld"
+
+program hello
+  write(*, *) HELLO
+end program hello
+
diff --git a/clang/test/Driver/fortran.f95 b/clang/test/Driver/fortran.f95
index db3ff2da17e8..e364180a1f9c 100644
--- a/clang/test/Driver/fortran.f95
+++ b/clang/test/Driver/fortran.f95
@@ -1,6 +1,8 @@
 ! Check that the clang driver can invoke gcc to compile Fortran when in
 ! --driver-mode=clang. This is legacy behaviour - see also --driver-mode=flang.
 
+! UNSUPPORTED: classic_flang
+
 ! RUN: %clang -target x86_64-unknown-linux-gnu -integrated-as -c %s -### 2>&1 \
 ! RUN:   | FileCheck --check-prefix=CHECK-OBJECT %s
 ! CHECK-OBJECT: gcc
diff --git a/clang/test/Driver/gfortran.f90 b/clang/test/Driver/gfortran.f90
index c985428650ec..1276703b1f6e 100644
--- a/clang/test/Driver/gfortran.f90
+++ b/clang/test/Driver/gfortran.f90
@@ -1,4 +1,5 @@
 ! XFAIL: *
+! UNSUPPORTED: classic_flang
 ! Test that Clang can forward all of the flags which are documented as
 ! being supported by gfortran to GCC when falling back to GCC for
 ! a fortran input file.
diff --git a/clang/test/Driver/lit.local.cfg b/clang/test/Driver/lit.local.cfg
index 6370e9f92d89..5ec1f9a8fc71 100644
--- a/clang/test/Driver/lit.local.cfg
+++ b/clang/test/Driver/lit.local.cfg
@@ -12,6 +12,9 @@ config.suffixes = [
     ".f90",
     ".F90",
     ".f95",
+    '.F95',
+    '.f',
+    '.F',
     ".cu",
     ".rs",
     ".cl",
diff --git a/clang/test/lit.cfg.py b/clang/test/lit.cfg.py
index 68e038475a5c..bb6fb1ae5146 100644
--- a/clang/test/lit.cfg.py
+++ b/clang/test/lit.cfg.py
@@ -395,3 +395,6 @@ if "system-aix" in config.available_features:
 # possibly be present in system and user configuration files, so disable
 # default configs for the test runs.
 config.environment["CLANG_NO_DEFAULT_CONFIG"] = "1"
+
+if config.use_classic_flang:
+    config.available_features.add("classic_flang")
diff --git a/clang/test/lit.site.cfg.py.in b/clang/test/lit.site.cfg.py.in
index ef75770a2c3c..bc278740e0d0 100644
--- a/clang/test/lit.site.cfg.py.in
+++ b/clang/test/lit.site.cfg.py.in
@@ -41,6 +41,7 @@ config.llvm_external_lit = path(r"@LLVM_EXTERNAL_LIT@")
 config.standalone_build = @CLANG_BUILT_STANDALONE@
 config.ppc_linux_default_ieeelongdouble = @PPC_LINUX_DEFAULT_IEEELONGDOUBLE@
 config.have_llvm_driver = @LLVM_TOOL_LLVM_DRIVER_BUILD@
+config.use_classic_flang = @LLVM_ENABLE_CLASSIC_FLANG@
 
 import lit.llvm
 lit.llvm.initialize(lit_config, config)
diff --git a/clang/tools/driver/CMakeLists.txt b/clang/tools/driver/CMakeLists.txt
index 2182486f93a5..c269561fde69 100644
--- a/clang/tools/driver/CMakeLists.txt
+++ b/clang/tools/driver/CMakeLists.txt
@@ -59,7 +59,7 @@ endif()
 add_dependencies(clang clang-resource-headers)
 
 if(NOT CLANG_LINKS_TO_CREATE)
-  set(CLANG_LINKS_TO_CREATE clang++ clang-cl clang-cpp)
+  set(CLANG_LINKS_TO_CREATE clang++ clang-cl clang-cpp flang)
 endif()
 
 if (CLANG_ENABLE_HLSL)
-- 
2.24.3 (Apple Git-128)