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gcc/loop-split.patch

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Init gcc-9.3.0
2020-05-14 10:48:46 +08:00
diff --git a/gcc/params.def b/gcc/params.def
index 942447d77e6..df7d1f7c5e7 100644
--- a/gcc/params.def
+++ b/gcc/params.def
@@ -415,6 +415,12 @@ DEFPARAM(PARAM_MAX_UNSWITCH_LEVEL,
"The maximum number of unswitchings in a single loop.",
3, 0, 0)
+DEFPARAM(PARAM_MIN_LOOP_COND_SPLIT_PROB,
+ "min-loop-cond-split-prob",
+ "The minimum threshold for probability of semi-invariant condition "
+ "statement to trigger loop split.",
+ 30, 0, 100)
+
/* The maximum number of insns in loop header duplicated by the copy loop
headers pass. */
DEFPARAM(PARAM_MAX_LOOP_HEADER_INSNS,
diff --git a/gcc/testsuite/g++.dg/tree-ssa/loop-cond-split-1.C b/gcc/testsuite/g++.dg/tree-ssa/loop-cond-split-1.C
new file mode 100644
index 00000000000..0d679cb9035
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/loop-cond-split-1.C
@@ -0,0 +1,33 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-tree-lsplit-details" } */
+
+#include <string>
+#include <map>
+
+using namespace std;
+
+class A
+{
+public:
+ bool empty;
+ void set (string s);
+};
+
+class B
+{
+ map<int, string> m;
+ void f ();
+};
+
+extern A *ga;
+
+void B::f ()
+{
+ for (map<int, string>::iterator iter = m.begin (); iter != m.end (); ++iter)
+ {
+ if (ga->empty)
+ ga->set (iter->second);
+ }
+}
+
+/* { dg-final { scan-tree-dump-times "loop split on semi-invariant condition at false branch" 1 "lsplit" } } */
diff --git a/gcc/testsuite/gcc.dg/torture/pr55107.c b/gcc/testsuite/gcc.dg/torture/pr55107.c
index 2402716be30..d757c041220 100644
--- a/gcc/testsuite/gcc.dg/torture/pr55107.c
+++ b/gcc/testsuite/gcc.dg/torture/pr55107.c
@@ -1,4 +1,5 @@
/* { dg-do compile } */
+/* { dg-additional-options "-fno-split-loops" } */
typedef unsigned short uint16_t;
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/loop-cond-split-1.c b/gcc/testsuite/gcc.dg/tree-ssa/loop-cond-split-1.c
new file mode 100644
index 00000000000..feb776e8373
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/loop-cond-split-1.c
@@ -0,0 +1,97 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-tree-lsplit-details" } */
+
+extern const int step;
+
+int ga, gb;
+
+__attribute__((pure)) __attribute__((noinline)) int inc (int i)
+{
+ return i + step;
+}
+
+extern int do_something (void);
+
+void test1 (int n)
+{
+ int i;
+
+ for (i = 0; i < n; i = inc (i))
+ {
+ if (ga)
+ ga = do_something ();
+ }
+}
+
+void test2 (int n, int p)
+{
+ int i;
+ int v;
+
+ for (i = 0; i < n ; i = inc (i))
+ {
+ if (ga)
+ {
+ v = inc (2);
+ gb += 1;
+ }
+ else
+ {
+ v = p * p;
+ gb *= 3;
+ }
+
+ if (v < 10)
+ ga = do_something ();
+ }
+}
+
+void test3 (int n, int p)
+{
+ int i;
+ int c = p + 1;
+ int v;
+
+ for (i = 0; i < n ; i = inc (i))
+ {
+ if (c)
+ {
+ v = inc (c);
+ gb += 1;
+ }
+ else
+ {
+ v = p * p;
+ gb *= 3;
+ }
+
+ if (v < 10)
+ c = do_something ();
+ }
+}
+
+void test4 (int n, int p)
+{
+ int i;
+ int v;
+
+ for (i = 0; i < n ; i = inc (i))
+ {
+ if (ga)
+ {
+ v = inc (2);
+ if (gb > 16)
+ v = inc (5);
+ }
+ else
+ {
+ v = p * p;
+ gb += 2;
+ }
+
+ if (v < 10)
+ ga = do_something ();
+ }
+}
+
+/* { dg-final { scan-tree-dump-times "loop split on semi-invariant condition at false branch" 3 "lsplit" } } */
diff --git a/gcc/tree-ssa-loop-split.c b/gcc/tree-ssa-loop-split.c
index f5f083384bc..6302d044e09 100644
--- a/gcc/tree-ssa-loop-split.c
+++ b/gcc/tree-ssa-loop-split.c
@@ -32,7 +32,10 @@ along with GCC; see the file COPYING3. If not see
#include "tree-ssa-loop.h"
#include "tree-ssa-loop-manip.h"
#include "tree-into-ssa.h"
+#include "tree-inline.h"
+#include "tree-cfgcleanup.h"
#include "cfgloop.h"
+#include "params.h"
#include "tree-scalar-evolution.h"
#include "gimple-iterator.h"
#include "gimple-pretty-print.h"
@@ -40,7 +43,9 @@ along with GCC; see the file COPYING3. If not see
#include "gimple-fold.h"
#include "gimplify-me.h"
-/* This file implements loop splitting, i.e. transformation of loops like
+/* This file implements two kinds of loop splitting.
+
+ One transformation of loops like:
for (i = 0; i < 100; i++)
{
@@ -487,8 +492,9 @@ compute_new_first_bound (gimple_seq *stmts, class tree_niter_desc *niter,
single exit of LOOP. */
static bool
-split_loop (struct loop *loop1, struct tree_niter_desc *niter)
+split_loop (struct loop *loop1)
{
+ struct tree_niter_desc niter;
basic_block *bbs;
unsigned i;
bool changed = false;
@@ -496,8 +502,28 @@ split_loop (class loop *loop1, class tree_niter_desc *niter)
tree border = NULL_TREE;
affine_iv iv;
+ if (!single_exit (loop1)
+ /* ??? We could handle non-empty latches when we split the latch edge
+ (not the exit edge), and put the new exit condition in the new block.
+ OTOH this executes some code unconditionally that might have been
+ skipped by the original exit before. */
+ || !empty_block_p (loop1->latch)
+ || !easy_exit_values (loop1)
+ || !number_of_iterations_exit (loop1, single_exit (loop1), &niter,
+ false, true)
+ || niter.cmp == ERROR_MARK
+ /* We can't yet handle loops controlled by a != predicate. */
+ || niter.cmp == NE_EXPR)
+ return false;
+
bbs = get_loop_body (loop1);
+ if (!can_copy_bbs_p (bbs, loop1->num_nodes))
+ {
+ free (bbs);
+ return false;
+ }
+
/* Find a splitting opportunity. */
for (i = 0; i < loop1->num_nodes; i++)
if ((guard_iv = split_at_bb_p (loop1, bbs[i], &border, &iv)))
@@ -505,8 +531,8 @@ split_loop (class loop *loop1, class tree_niter_desc *niter)
/* Handling opposite steps is not implemented yet. Neither
is handling different step sizes. */
if ((tree_int_cst_sign_bit (iv.step)
- != tree_int_cst_sign_bit (niter->control.step))
- || !tree_int_cst_equal (iv.step, niter->control.step))
+ != tree_int_cst_sign_bit (niter.control.step))
+ || !tree_int_cst_equal (iv.step, niter.control.step))
continue;
/* Find a loop PHI node that defines guard_iv directly,
@@ -575,7 +601,7 @@ split_loop (class loop *loop1, class tree_niter_desc *niter)
Compute the new bound for the guarding IV and patch the
loop exit to use it instead of original IV and bound. */
gimple_seq stmts = NULL;
- tree newend = compute_new_first_bound (&stmts, niter, border,
+ tree newend = compute_new_first_bound (&stmts, &niter, border,
guard_code, guard_init);
if (stmts)
gsi_insert_seq_on_edge_immediate (loop_preheader_edge (loop1),
@@ -612,6 +638,956 @@ split_loop (class loop *loop1, class tree_niter_desc *niter)
return changed;
}
+/* Another transformation of loops like:
+
+ for (i = INIT (); CHECK (i); i = NEXT ())
+ {
+ if (expr (a_1, a_2, ..., a_n)) // expr is pure
+ a_j = ...; // change at least one a_j
+ else
+ S; // not change any a_j
+ }
+
+ into:
+
+ for (i = INIT (); CHECK (i); i = NEXT ())
+ {
+ if (expr (a_1, a_2, ..., a_n))
+ a_j = ...;
+ else
+ {
+ S;
+ i = NEXT ();
+ break;
+ }
+ }
+
+ for (; CHECK (i); i = NEXT ())
+ {
+ S;
+ }
+
+ */
+
+/* Data structure to hold temporary information during loop split upon
+ semi-invariant conditional statement. */
+class split_info {
+public:
+ /* Array of all basic blocks in a loop, returned by get_loop_body(). */
+ basic_block *bbs;
+
+ /* All memory store/clobber statements in a loop. */
+ auto_vec<gimple *> memory_stores;
+
+ /* Whether above memory stores vector has been filled. */
+ int need_init;
+
+ /* Control dependencies of basic blocks in a loop. */
+ auto_vec<hash_set<basic_block> *> control_deps;
+
+ split_info () : bbs (NULL), need_init (true) { }
+
+ ~split_info ()
+ {
+ if (bbs)
+ free (bbs);
+
+ for (unsigned i = 0; i < control_deps.length (); i++)
+ delete control_deps[i];
+ }
+};
+
+/* Find all statements with memory-write effect in LOOP, including memory
+ store and non-pure function call, and keep those in a vector. This work
+ is only done one time, for the vector should be constant during analysis
+ stage of semi-invariant condition. */
+
+static void
+find_vdef_in_loop (struct loop *loop)
+{
+ split_info *info = (split_info *) loop->aux;
+ gphi *vphi = get_virtual_phi (loop->header);
+
+ /* Indicate memory store vector has been filled. */
+ info->need_init = false;
+
+ /* If loop contains memory operation, there must be a virtual PHI node in
+ loop header basic block. */
+ if (vphi == NULL)
+ return;
+
+ /* All virtual SSA names inside the loop are connected to be a cyclic
+ graph via virtual PHI nodes. The virtual PHI node in loop header just
+ links the first and the last virtual SSA names, by using the last as
+ PHI operand to define the first. */
+ const edge latch = loop_latch_edge (loop);
+ const tree first = gimple_phi_result (vphi);
+ const tree last = PHI_ARG_DEF_FROM_EDGE (vphi, latch);
+
+ /* The virtual SSA cyclic graph might consist of only one SSA name, who
+ is defined by itself.
+
+ .MEM_1 = PHI <.MEM_2(loop entry edge), .MEM_1(latch edge)>
+
+ This means the loop contains only memory loads, so we can skip it. */
+ if (first == last)
+ return;
+
+ auto_vec<gimple *> other_stores;
+ auto_vec<tree> worklist;
+ auto_bitmap visited;
+
+ bitmap_set_bit (visited, SSA_NAME_VERSION (first));
+ bitmap_set_bit (visited, SSA_NAME_VERSION (last));
+ worklist.safe_push (last);
+
+ do
+ {
+ tree vuse = worklist.pop ();
+ gimple *stmt = SSA_NAME_DEF_STMT (vuse);
+
+ /* We mark the first and last SSA names as visited at the beginning,
+ and reversely start the process from the last SSA name towards the
+ first, which ensures that this do-while will not touch SSA names
+ defined outside the loop. */
+ gcc_assert (gimple_bb (stmt)
+ && flow_bb_inside_loop_p (loop, gimple_bb (stmt)));
+
+ if (gimple_code (stmt) == GIMPLE_PHI)
+ {
+ gphi *phi = as_a <gphi *> (stmt);
+
+ for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i)
+ {
+ tree arg = gimple_phi_arg_def (stmt, i);
+
+ if (bitmap_set_bit (visited, SSA_NAME_VERSION (arg)))
+ worklist.safe_push (arg);
+ }
+ }
+ else
+ {
+ tree prev = gimple_vuse (stmt);
+
+ /* Non-pure call statement is conservatively assumed to impact all
+ memory locations. So place call statements ahead of other memory
+ stores in the vector with an idea of of using them as shortcut
+ terminators to memory alias analysis. */
+ if (gimple_code (stmt) == GIMPLE_CALL)
+ info->memory_stores.safe_push (stmt);
+ else
+ other_stores.safe_push (stmt);
+
+ if (bitmap_set_bit (visited, SSA_NAME_VERSION (prev)))
+ worklist.safe_push (prev);
+ }
+ } while (!worklist.is_empty ());
+
+ info->memory_stores.safe_splice (other_stores);
+}
+
+/* Two basic blocks have equivalent control dependency if one dominates to
+ the other, and it is post-dominated by the latter. Given a basic block
+ BB in LOOP, find farest equivalent dominating basic block. For BB, there
+ is a constraint that BB does not post-dominate loop header of LOOP, this
+ means BB is control-dependent on at least one basic block in LOOP. */
+
+static basic_block
+get_control_equiv_head_block (struct loop *loop, basic_block bb)
+{
+ while (!bb->aux)
+ {
+ basic_block dom_bb = get_immediate_dominator (CDI_DOMINATORS, bb);
+
+ gcc_checking_assert (dom_bb && flow_bb_inside_loop_p (loop, dom_bb));
+
+ if (!dominated_by_p (CDI_POST_DOMINATORS, dom_bb, bb))
+ break;
+
+ bb = dom_bb;
+ }
+ return bb;
+}
+
+/* Given a BB in LOOP, find out all basic blocks in LOOP that BB is control-
+ dependent on. */
+
+static hash_set<basic_block> *
+find_control_dep_blocks (struct loop *loop, basic_block bb)
+{
+ /* BB has same control dependency as loop header, then it is not control-
+ dependent on any basic block in LOOP. */
+ if (dominated_by_p (CDI_POST_DOMINATORS, loop->header, bb))
+ return NULL;
+
+ basic_block equiv_head = get_control_equiv_head_block (loop, bb);
+
+ if (equiv_head->aux)
+ {
+ /* There is a basic block containing control dependency equivalent
+ to BB. No need to recompute that, and also set this information
+ to other equivalent basic blocks. */
+ for (; bb != equiv_head;
+ bb = get_immediate_dominator (CDI_DOMINATORS, bb))
+ bb->aux = equiv_head->aux;
+ return (hash_set<basic_block> *) equiv_head->aux;
+ }
+
+ /* A basic block X is control-dependent on another Y iff there exists
+ a path from X to Y, in which every basic block other than X and Y
+ is post-dominated by Y, but X is not post-dominated by Y.
+
+ According to this rule, traverse basic blocks in the loop backwards
+ starting from BB, if a basic block is post-dominated by BB, extend
+ current post-dominating path to this block, otherwise it is another
+ one that BB is control-dependent on. */
+
+ auto_vec<basic_block> pdom_worklist;
+ hash_set<basic_block> pdom_visited;
+ hash_set<basic_block> *dep_bbs = new hash_set<basic_block>;
+
+ pdom_worklist.safe_push (equiv_head);
+
+ do
+ {
+ basic_block pdom_bb = pdom_worklist.pop ();
+ edge_iterator ei;
+ edge e;
+
+ if (pdom_visited.add (pdom_bb))
+ continue;
+
+ FOR_EACH_EDGE (e, ei, pdom_bb->preds)
+ {
+ basic_block pred_bb = e->src;
+
+ if (!dominated_by_p (CDI_POST_DOMINATORS, pred_bb, bb))
+ {
+ dep_bbs->add (pred_bb);
+ continue;
+ }
+
+ pred_bb = get_control_equiv_head_block (loop, pred_bb);
+
+ if (pdom_visited.contains (pred_bb))
+ continue;
+
+ if (!pred_bb->aux)
+ {
+ pdom_worklist.safe_push (pred_bb);
+ continue;
+ }
+
+ /* If control dependency of basic block is available, fast extend
+ post-dominating path using the information instead of advancing
+ forward step-by-step. */
+ hash_set<basic_block> *pred_dep_bbs
+ = (hash_set<basic_block> *) pred_bb->aux;
+
+ for (hash_set<basic_block>::iterator iter = pred_dep_bbs->begin ();
+ iter != pred_dep_bbs->end (); ++iter)
+ {
+ basic_block pred_dep_bb = *iter;
+
+ /* Basic blocks can either be in control dependency of BB, or
+ must be post-dominated by BB, if so, extend the path from
+ these basic blocks. */
+ if (!dominated_by_p (CDI_POST_DOMINATORS, pred_dep_bb, bb))
+ dep_bbs->add (pred_dep_bb);
+ else if (!pdom_visited.contains (pred_dep_bb))
+ pdom_worklist.safe_push (pred_dep_bb);
+ }
+ }
+ } while (!pdom_worklist.is_empty ());
+
+ /* Record computed control dependencies in loop so that we can reach them
+ when reclaiming resources. */
+ ((split_info *) loop->aux)->control_deps.safe_push (dep_bbs);
+
+ /* Associate control dependence with related equivalent basic blocks. */
+ for (equiv_head->aux = dep_bbs; bb != equiv_head;
+ bb = get_immediate_dominator (CDI_DOMINATORS, bb))
+ bb->aux = dep_bbs;
+
+ return dep_bbs;
+}
+
+/* Forward declaration */
+
+static bool
+stmt_semi_invariant_p_1 (struct loop *loop, gimple *stmt,
+ const_basic_block skip_head,
+ hash_map<gimple *, bool> &stmt_stat);
+
+/* Given STMT, memory load or pure call statement, check whether it is impacted
+ by some memory store in LOOP, excluding trace starting from SKIP_HEAD (the
+ trace is composed of SKIP_HEAD and those basic block dominated by it, always
+ corresponds to one branch of a conditional statement). If SKIP_HEAD is
+ NULL, all basic blocks of LOOP are checked. */
+
+static bool
+vuse_semi_invariant_p (struct loop *loop, gimple *stmt,
+ const_basic_block skip_head)
+{
+ split_info *info = (split_info *) loop->aux;
+ tree rhs = NULL_TREE;
+ ao_ref ref;
+ gimple *store;
+ unsigned i;
+
+ /* Collect memory store/clobber statements if haven't done that. */
+ if (info->need_init)
+ find_vdef_in_loop (loop);
+
+ if (is_gimple_assign (stmt))
+ rhs = gimple_assign_rhs1 (stmt);
+
+ ao_ref_init (&ref, rhs);
+
+ FOR_EACH_VEC_ELT (info->memory_stores, i, store)
+ {
+ /* Skip basic blocks dominated by SKIP_HEAD, if non-NULL. */
+ if (skip_head
+ && dominated_by_p (CDI_DOMINATORS, gimple_bb (store), skip_head))
+ continue;
+
+ if (!ref.ref || stmt_may_clobber_ref_p_1 (store, &ref))
+ return false;
+ }
+
+ return true;
+}
+
+/* Suppose one condition branch, led by SKIP_HEAD, is not executed since
+ certain iteration of LOOP, check whether an SSA name (NAME) remains
+ unchanged in next iteration. We call this characteristic semi-
+ invariantness. SKIP_HEAD might be NULL, if so, nothing excluded, all basic
+ blocks and control flows in the loop will be considered. Semi-invariant
+ state of checked statement is cached in hash map STMT_STAT to avoid
+ redundant computation in possible following re-check. */
+
+static inline bool
+ssa_semi_invariant_p (struct loop *loop, tree name,
+ const_basic_block skip_head,
+ hash_map<gimple *, bool> &stmt_stat)
+{
+ gimple *def = SSA_NAME_DEF_STMT (name);
+ const_basic_block def_bb = gimple_bb (def);
+
+ /* An SSA name defined outside loop is definitely semi-invariant. */
+ if (!def_bb || !flow_bb_inside_loop_p (loop, def_bb))
+ return true;
+
+ return stmt_semi_invariant_p_1 (loop, def, skip_head, stmt_stat);
+}
+
+/* Check whether a loop iteration PHI node (LOOP_PHI) defines a value that is
+ semi-invariant in LOOP. Basic blocks dominated by SKIP_HEAD (if non-NULL),
+ are excluded from LOOP. */
+
+static bool
+loop_iter_phi_semi_invariant_p (struct loop *loop, gphi *loop_phi,
+ const_basic_block skip_head)
+{
+ const_edge latch = loop_latch_edge (loop);
+ tree name = gimple_phi_result (loop_phi);
+ tree from = PHI_ARG_DEF_FROM_EDGE (loop_phi, latch);
+
+ gcc_checking_assert (from);
+
+ /* Loop iteration PHI node locates in loop header, and it has two source
+ operands, one is an initial value coming from outside the loop, the other
+ is a value through latch of the loop, which is derived in last iteration,
+ we call the latter latch value. From the PHI node to definition of latch
+ value, if excluding branch trace starting from SKIP_HEAD, except copy-
+ assignment or likewise, there is no other kind of value redefinition, SSA
+ name defined by the PHI node is semi-invariant.
+
+ loop entry
+ | .--- latch ---.
+ | | |
+ v v |
+ x_1 = PHI <x_0, x_3> |
+ | |
+ v |
+ .------- if (cond) -------. |
+ | | |
+ | [ SKIP ] |
+ | | |
+ | x_2 = ... |
+ | | |
+ '---- T ---->.<---- F ----' |
+ | |
+ v |
+ x_3 = PHI <x_1, x_2> |
+ | |
+ '----------------------'
+
+ Suppose in certain iteration, execution flow in above graph goes through
+ true branch, which means that one source value to define x_3 in false
+ branch (x_2) is skipped, x_3 only comes from x_1, and x_1 in next
+ iterations is defined by x_3, we know that x_1 will never changed if COND
+ always chooses true branch from then on. */
+
+ while (from != name)
+ {
+ /* A new value comes from a CONSTANT. */
+ if (TREE_CODE (from) != SSA_NAME)
+ return false;
+
+ gimple *stmt = SSA_NAME_DEF_STMT (from);
+ const_basic_block bb = gimple_bb (stmt);
+
+ /* A new value comes from outside the loop. */
+ if (!bb || !flow_bb_inside_loop_p (loop, bb))
+ return false;
+
+ from = NULL_TREE;
+
+ if (gimple_code (stmt) == GIMPLE_PHI)
+ {
+ gphi *phi = as_a <gphi *> (stmt);
+
+ for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i)
+ {
+ if (skip_head)
+ {
+ const_edge e = gimple_phi_arg_edge (phi, i);
+
+ /* Don't consider redefinitions in excluded basic blocks. */
+ if (dominated_by_p (CDI_DOMINATORS, e->src, skip_head))
+ continue;
+ }
+
+ tree arg = gimple_phi_arg_def (phi, i);
+
+ if (!from)
+ from = arg;
+ else if (!operand_equal_p (from, arg, 0))
+ /* There are more than one source operands that provide
+ different values to the SSA name, it is variant. */
+ return false;
+ }
+ }
+ else if (gimple_code (stmt) == GIMPLE_ASSIGN)
+ {
+ /* For simple value copy, check its rhs instead. */
+ if (gimple_assign_ssa_name_copy_p (stmt))
+ from = gimple_assign_rhs1 (stmt);
+ }
+
+ /* Any other kind of definition is deemed to introduce a new value
+ to the SSA name. */
+ if (!from)
+ return false;
+ }
+ return true;
+}
+
+/* Check whether conditional predicates that BB is control-dependent on, are
+ semi-invariant in LOOP. Basic blocks dominated by SKIP_HEAD (if non-NULL),
+ are excluded from LOOP. Semi-invariant state of checked statement is cached
+ in hash map STMT_STAT. */
+
+static bool
+control_dep_semi_invariant_p (struct loop *loop, basic_block bb,
+ const_basic_block skip_head,
+ hash_map<gimple *, bool> &stmt_stat)
+{
+ hash_set<basic_block> *dep_bbs = find_control_dep_blocks (loop, bb);
+
+ if (!dep_bbs)
+ return true;
+
+ for (hash_set<basic_block>::iterator iter = dep_bbs->begin ();
+ iter != dep_bbs->end (); ++iter)
+ {
+ gimple *last = last_stmt (*iter);
+
+ if (!last)
+ return false;
+
+ /* Only check condition predicates. */
+ if (gimple_code (last) != GIMPLE_COND
+ && gimple_code (last) != GIMPLE_SWITCH)
+ return false;
+
+ if (!stmt_semi_invariant_p_1 (loop, last, skip_head, stmt_stat))
+ return false;
+ }
+
+ return true;
+}
+
+/* Check whether STMT is semi-invariant in LOOP, iff all its operands are
+ semi-invariant, consequently, all its defined values are semi-invariant.
+ Basic blocks dominated by SKIP_HEAD (if non-NULL), are excluded from LOOP.
+ Semi-invariant state of checked statement is cached in hash map
+ STMT_STAT. */
+
+static bool
+stmt_semi_invariant_p_1 (struct loop *loop, gimple *stmt,
+ const_basic_block skip_head,
+ hash_map<gimple *, bool> &stmt_stat)
+{
+ bool existed;
+ bool &invar = stmt_stat.get_or_insert (stmt, &existed);
+
+ if (existed)
+ return invar;
+
+ /* A statement might depend on itself, which is treated as variant. So set
+ state of statement under check to be variant to ensure that. */
+ invar = false;
+
+ if (gimple_code (stmt) == GIMPLE_PHI)
+ {
+ gphi *phi = as_a <gphi *> (stmt);
+
+ if (gimple_bb (stmt) == loop->header)
+ {
+ invar = loop_iter_phi_semi_invariant_p (loop, phi, skip_head);
+ return invar;
+ }
+
+ /* For a loop PHI node that does not locate in loop header, it is semi-
+ invariant only if two conditions are met. The first is its source
+ values are derived from CONSTANT (including loop-invariant value), or
+ from SSA name defined by semi-invariant loop iteration PHI node. The
+ second is its source incoming edges are control-dependent on semi-
+ invariant conditional predicates. */
+ for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i)
+ {
+ const_edge e = gimple_phi_arg_edge (phi, i);
+ tree arg = gimple_phi_arg_def (phi, i);
+
+ if (TREE_CODE (arg) == SSA_NAME)
+ {
+ if (!ssa_semi_invariant_p (loop, arg, skip_head, stmt_stat))
+ return false;
+
+ /* If source value is defined in location from where the source
+ edge comes in, no need to check control dependency again
+ since this has been done in above SSA name check stage. */
+ if (e->src == gimple_bb (SSA_NAME_DEF_STMT (arg)))
+ continue;
+ }
+
+ if (!control_dep_semi_invariant_p (loop, e->src, skip_head,
+ stmt_stat))
+ return false;
+ }
+ }
+ else
+ {
+ ssa_op_iter iter;
+ tree use;
+
+ /* Volatile memory load or return of normal (non-const/non-pure) call
+ should not be treated as constant in each iteration of loop. */
+ if (gimple_has_side_effects (stmt))
+ return false;
+
+ /* Check if any memory store may kill memory load at this place. */
+ if (gimple_vuse (stmt) && !vuse_semi_invariant_p (loop, stmt, skip_head))
+ return false;
+
+ /* Although operand of a statement might be SSA name, CONSTANT or
+ VARDECL, here we only need to check SSA name operands. This is
+ because check on VARDECL operands, which involve memory loads,
+ must have been done prior to invocation of this function in
+ vuse_semi_invariant_p. */
+ FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
+ if (!ssa_semi_invariant_p (loop, use, skip_head, stmt_stat))
+ return false;
+ }
+
+ if (!control_dep_semi_invariant_p (loop, gimple_bb (stmt), skip_head,
+ stmt_stat))
+ return false;
+
+ /* Here we SHOULD NOT use invar = true, since hash map might be changed due
+ to new insertion, and thus invar may point to invalid memory. */
+ stmt_stat.put (stmt, true);
+ return true;
+}
+
+/* A helper function to check whether STMT is semi-invariant in LOOP. Basic
+ blocks dominated by SKIP_HEAD (if non-NULL), are excluded from LOOP. */
+
+static bool
+stmt_semi_invariant_p (struct loop *loop, gimple *stmt,
+ const_basic_block skip_head)
+{
+ hash_map<gimple *, bool> stmt_stat;
+ return stmt_semi_invariant_p_1 (loop, stmt, skip_head, stmt_stat);
+}
+
+/* Determine when conditional statement never transfers execution to one of its
+ branch, whether we can remove the branch's leading basic block (BRANCH_BB)
+ and those basic blocks dominated by BRANCH_BB. */
+
+static bool
+branch_removable_p (basic_block branch_bb)
+{
+ edge_iterator ei;
+ edge e;
+
+ if (single_pred_p (branch_bb))
+ return true;
+
+ FOR_EACH_EDGE (e, ei, branch_bb->preds)
+ {
+ if (dominated_by_p (CDI_DOMINATORS, e->src, branch_bb))
+ continue;
+
+ if (dominated_by_p (CDI_DOMINATORS, branch_bb, e->src))
+ continue;
+
+ /* The branch can be reached from opposite branch, or from some
+ statement not dominated by the conditional statement. */
+ return false;
+ }
+
+ return true;
+}
+
+/* Find out which branch of a conditional statement (COND) is invariant in the
+ execution context of LOOP. That is: once the branch is selected in certain
+ iteration of the loop, any operand that contributes to computation of the
+ conditional statement remains unchanged in all following iterations. */
+
+static edge
+get_cond_invariant_branch (struct loop *loop, gcond *cond)
+{
+ basic_block cond_bb = gimple_bb (cond);
+ basic_block targ_bb[2];
+ bool invar[2];
+ unsigned invar_checks = 0;
+
+ for (unsigned i = 0; i < 2; i++)
+ {
+ targ_bb[i] = EDGE_SUCC (cond_bb, i)->dest;
+
+ /* One branch directs to loop exit, no need to perform loop split upon
+ this conditional statement. Firstly, it is trivial if the exit branch
+ is semi-invariant, for the statement is just to break loop. Secondly,
+ if the opposite branch is semi-invariant, it means that the statement
+ is real loop-invariant, which is covered by loop unswitch. */
+ if (!flow_bb_inside_loop_p (loop, targ_bb[i]))
+ return NULL;
+ }
+
+ for (unsigned i = 0; i < 2; i++)
+ {
+ invar[!i] = false;
+
+ if (!branch_removable_p (targ_bb[i]))
+ continue;
+
+ /* Given a semi-invariant branch, if its opposite branch dominates
+ loop latch, it and its following trace will only be executed in
+ final iteration of loop, namely it is not part of repeated body
+ of the loop. Similar to the above case that the branch is loop
+ exit, no need to split loop. */
+ if (dominated_by_p (CDI_DOMINATORS, loop->latch, targ_bb[i]))
+ continue;
+
+ invar[!i] = stmt_semi_invariant_p (loop, cond, targ_bb[i]);
+ invar_checks++;
+ }
+
+ /* With both branches being invariant (handled by loop unswitch) or
+ variant is not what we want. */
+ if (invar[0] ^ !invar[1])
+ return NULL;
+
+ /* Found a real loop-invariant condition, do nothing. */
+ if (invar_checks < 2 && stmt_semi_invariant_p (loop, cond, NULL))
+ return NULL;
+
+ return EDGE_SUCC (cond_bb, invar[0] ? 0 : 1);
+}
+
+/* Calculate increased code size measured by estimated insn number if applying
+ loop split upon certain branch (BRANCH_EDGE) of a conditional statement. */
+
+static int
+compute_added_num_insns (struct loop *loop, const_edge branch_edge)
+{
+ basic_block cond_bb = branch_edge->src;
+ unsigned branch = EDGE_SUCC (cond_bb, 1) == branch_edge;
+ basic_block opposite_bb = EDGE_SUCC (cond_bb, !branch)->dest;
+ basic_block *bbs = ((split_info *) loop->aux)->bbs;
+ int num = 0;
+
+ for (unsigned i = 0; i < loop->num_nodes; i++)
+ {
+ /* Do no count basic blocks only in opposite branch. */
+ if (dominated_by_p (CDI_DOMINATORS, bbs[i], opposite_bb))
+ continue;
+
+ num += estimate_num_insns_seq (bb_seq (bbs[i]), &eni_size_weights);
+ }
+
+ /* It is unnecessary to evaluate expression of the conditional statement
+ in new loop that contains only invariant branch. This expression should
+ be constant value (either true or false). Exclude code size of insns
+ that contribute to computation of the expression. */
+
+ auto_vec<gimple *> worklist;
+ hash_set<gimple *> removed;
+ gimple *stmt = last_stmt (cond_bb);
+
+ worklist.safe_push (stmt);
+ removed.add (stmt);
+ num -= estimate_num_insns (stmt, &eni_size_weights);
+
+ do
+ {
+ ssa_op_iter opnd_iter;
+ use_operand_p opnd_p;
+
+ stmt = worklist.pop ();
+ FOR_EACH_PHI_OR_STMT_USE (opnd_p, stmt, opnd_iter, SSA_OP_USE)
+ {
+ tree opnd = USE_FROM_PTR (opnd_p);
+
+ if (TREE_CODE (opnd) != SSA_NAME || SSA_NAME_IS_DEFAULT_DEF (opnd))
+ continue;
+
+ gimple *opnd_stmt = SSA_NAME_DEF_STMT (opnd);
+ use_operand_p use_p;
+ imm_use_iterator use_iter;
+
+ if (removed.contains (opnd_stmt)
+ || !flow_bb_inside_loop_p (loop, gimple_bb (opnd_stmt)))
+ continue;
+
+ FOR_EACH_IMM_USE_FAST (use_p, use_iter, opnd)
+ {
+ gimple *use_stmt = USE_STMT (use_p);
+
+ if (!is_gimple_debug (use_stmt) && !removed.contains (use_stmt))
+ {
+ opnd_stmt = NULL;
+ break;
+ }
+ }
+
+ if (opnd_stmt)
+ {
+ worklist.safe_push (opnd_stmt);
+ removed.add (opnd_stmt);
+ num -= estimate_num_insns (opnd_stmt, &eni_size_weights);
+ }
+ }
+ } while (!worklist.is_empty ());
+
+ gcc_assert (num >= 0);
+ return num;
+}
+
+/* Find out loop-invariant branch of a conditional statement (COND) if it has,
+ and check whether it is eligible and profitable to perform loop split upon
+ this branch in LOOP. */
+
+static edge
+get_cond_branch_to_split_loop (struct loop *loop, gcond *cond)
+{
+ edge invar_branch = get_cond_invariant_branch (loop, cond);
+ if (!invar_branch)
+ return NULL;
+
+ /* When accurate profile information is available, and execution
+ frequency of the branch is too low, just let it go. */
+ profile_probability prob = invar_branch->probability;
+ if (prob.reliable_p ())
+ {
+ int thres = PARAM_VALUE (PARAM_MIN_LOOP_COND_SPLIT_PROB);
+
+ if (prob < profile_probability::always ().apply_scale (thres, 100))
+ return NULL;
+ }
+
+ /* Add a threshold for increased code size to disable loop split. */
+ if (compute_added_num_insns (loop, invar_branch)
+ > PARAM_VALUE (PARAM_MAX_PEELED_INSNS))
+ return NULL;
+
+ return invar_branch;
+}
+
+/* Given a loop (LOOP1) with a loop-invariant branch (INVAR_BRANCH) of some
+ conditional statement, perform loop split transformation illustrated
+ as the following graph.
+
+ .-------T------ if (true) ------F------.
+ | .---------------. |
+ | | | |
+ v | v v
+ pre-header | pre-header
+ | .------------. | | .------------.
+ | | | | | | |
+ | v | | | v |
+ header | | header |
+ | | | | |
+ .--- if (cond) ---. | | .--- if (true) ---. |
+ | | | | | | |
+ invariant | | | invariant | |
+ | | | | | | |
+ '---T--->.<---F---' | | '---T--->.<---F---' |
+ | | / | |
+ stmts | / stmts |
+ | F T | |
+ / \ | / / \ |
+ .-------* * [ if (cond) ] .-------* * |
+ | | | | | |
+ | latch | | latch |
+ | | | | | |
+ | '------------' | '------------'
+ '------------------------. .-----------'
+ loop1 | | loop2
+ v v
+ exits
+
+ In the graph, loop1 represents the part derived from original one, and
+ loop2 is duplicated using loop_version (), which corresponds to the part
+ of original one being splitted out. In original latch edge of loop1, we
+ insert a new conditional statement duplicated from the semi-invariant cond,
+ and one of its branch goes back to loop1 header as a latch edge, and the
+ other branch goes to loop2 pre-header as an entry edge. And also in loop2,
+ we abandon the variant branch of the conditional statement by setting a
+ constant bool condition, based on which branch is semi-invariant. */
+
+static bool
+do_split_loop_on_cond (struct loop *loop1, edge invar_branch)
+{
+ basic_block cond_bb = invar_branch->src;
+ bool true_invar = !!(invar_branch->flags & EDGE_TRUE_VALUE);
+ gcond *cond = as_a <gcond *> (last_stmt (cond_bb));
+
+ gcc_assert (cond_bb->loop_father == loop1);
+
+ if (dump_enabled_p ())
+ dump_printf_loc (MSG_OPTIMIZED_LOCATIONS, cond,
+ "loop split on semi-invariant condition at %s branch\n",
+ true_invar ? "true" : "false");
+
+ initialize_original_copy_tables ();
+
+ struct loop *loop2 = loop_version (loop1, boolean_true_node, NULL,
+ profile_probability::always (),
+ profile_probability::never (),
+ profile_probability::always (),
+ profile_probability::always (),
+ true);
+ if (!loop2)
+ {
+ free_original_copy_tables ();
+ return false;
+ }
+
+ basic_block cond_bb_copy = get_bb_copy (cond_bb);
+ gcond *cond_copy = as_a<gcond *> (last_stmt (cond_bb_copy));
+
+ /* Replace the condition in loop2 with a bool constant to let PassManager
+ remove the variant branch after current pass completes. */
+ if (true_invar)
+ gimple_cond_make_true (cond_copy);
+ else
+ gimple_cond_make_false (cond_copy);
+
+ update_stmt (cond_copy);
+
+ /* Insert a new conditional statement on latch edge of loop1, its condition
+ is duplicated from the semi-invariant. This statement acts as a switch
+ to transfer execution from loop1 to loop2, when loop1 enters into
+ invariant state. */
+ basic_block latch_bb = split_edge (loop_latch_edge (loop1));
+ basic_block break_bb = split_edge (single_pred_edge (latch_bb));
+ gimple *break_cond = gimple_build_cond (gimple_cond_code(cond),
+ gimple_cond_lhs (cond),
+ gimple_cond_rhs (cond),
+ NULL_TREE, NULL_TREE);
+
+ gimple_stmt_iterator gsi = gsi_last_bb (break_bb);
+ gsi_insert_after (&gsi, break_cond, GSI_NEW_STMT);
+
+ edge to_loop1 = single_succ_edge (break_bb);
+ edge to_loop2 = make_edge (break_bb, loop_preheader_edge (loop2)->src, 0);
+
+ to_loop1->flags &= ~EDGE_FALLTHRU;
+ to_loop1->flags |= true_invar ? EDGE_FALSE_VALUE : EDGE_TRUE_VALUE;
+ to_loop2->flags |= true_invar ? EDGE_TRUE_VALUE : EDGE_FALSE_VALUE;
+
+ update_ssa (TODO_update_ssa);
+
+ /* Due to introduction of a control flow edge from loop1 latch to loop2
+ pre-header, we should update PHIs in loop2 to reflect this connection
+ between loop1 and loop2. */
+ connect_loop_phis (loop1, loop2, to_loop2);
+
+ free_original_copy_tables ();
+
+ rewrite_into_loop_closed_ssa_1 (NULL, 0, SSA_OP_USE, loop1);
+
+ return true;
+}
+
+/* Traverse all conditional statements in LOOP, to find out a good candidate
+ upon which we can do loop split. */
+
+static bool
+split_loop_on_cond (struct loop *loop)
+{
+ split_info *info = new split_info ();
+ basic_block *bbs = info->bbs = get_loop_body (loop);
+ bool do_split = false;
+
+ /* Allocate an area to keep temporary info, and associate its address
+ with loop aux field. */
+ loop->aux = info;
+
+ for (unsigned i = 0; i < loop->num_nodes; i++)
+ bbs[i]->aux = NULL;
+
+ for (unsigned i = 0; i < loop->num_nodes; i++)
+ {
+ basic_block bb = bbs[i];
+
+ /* We only consider conditional statement, which be executed at most once
+ in each iteration of the loop. So skip statements in inner loops. */
+ if ((bb->loop_father != loop) || (bb->flags & BB_IRREDUCIBLE_LOOP))
+ continue;
+
+ /* Actually this check is not a must constraint. With it, we can ensure
+ conditional statement will always be executed in each iteration. */
+ if (!dominated_by_p (CDI_DOMINATORS, loop->latch, bb))
+ continue;
+
+ gimple *last = last_stmt (bb);
+
+ if (!last || gimple_code (last) != GIMPLE_COND)
+ continue;
+
+ gcond *cond = as_a <gcond *> (last);
+ edge branch_edge = get_cond_branch_to_split_loop (loop, cond);
+
+ if (branch_edge)
+ {
+ do_split_loop_on_cond (loop, branch_edge);
+ do_split = true;
+ break;
+ }
+ }
+
+ delete info;
+ loop->aux = NULL;
+
+ return do_split;
+}
+
/* Main entry point. Perform loop splitting on all suitable loops. */
static unsigned int
@@ -621,13 +1597,15 @@ tree_ssa_split_loops (void)
bool changed = false;
gcc_assert (scev_initialized_p ());
+
+ calculate_dominance_info (CDI_POST_DOMINATORS);
+
FOR_EACH_LOOP (loop, LI_INCLUDE_ROOT)
loop->aux = NULL;
/* Go through all loops starting from innermost. */
FOR_EACH_LOOP (loop, LI_FROM_INNERMOST)
{
- struct tree_niter_desc niter;
if (loop->aux)
{
/* If any of our inner loops was split, don't split us,
@@ -636,35 +1614,24 @@ tree_ssa_split_loops (void)
continue;
}
- if (single_exit (loop)
- /* ??? We could handle non-empty latches when we split
- the latch edge (not the exit edge), and put the new
- exit condition in the new block. OTOH this executes some
- code unconditionally that might have been skipped by the
- original exit before. */
- && empty_block_p (loop->latch)
- && !optimize_loop_for_size_p (loop)
- && easy_exit_values (loop)
- && number_of_iterations_exit (loop, single_exit (loop), &niter,
- false, true)
- && niter.cmp != ERROR_MARK
- /* We can't yet handle loops controlled by a != predicate. */
- && niter.cmp != NE_EXPR
- && can_duplicate_loop_p (loop))
+ if (optimize_loop_for_size_p (loop))
+ continue;
+
+ if (split_loop (loop) || split_loop_on_cond (loop))
{
- if (split_loop (loop, &niter))
- {
- /* Mark our containing loop as having had some split inner
- loops. */
- loop_outer (loop)->aux = loop;
- changed = true;
- }
+ /* Mark our containing loop as having had some split inner loops. */
+ loop_outer (loop)->aux = loop;
+ changed = true;
}
}
FOR_EACH_LOOP (loop, LI_INCLUDE_ROOT)
loop->aux = NULL;
+ clear_aux_for_blocks ();
+
+ free_dominance_info (CDI_POST_DOMINATORS);
+
if (changed)
return TODO_cleanup_cfg;
return 0;
Reference in New Issue Copy Permalink