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openjdk-1.8.0/8148754-C2-loop-unrolling-fails-due-to-unexpected-gr.patch
jdkboy 78c7e428f6 delete redundant info
2020-03-21 11:30:48 +08:00

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From be0206e834bab370da41cf9ec9e6b9be710e1987 Mon Sep 17 00:00:00 2001
Date: Fri, 19 Apr 2019 17:40:19 +0000
Subject: [PATCH] 8148754: C2 loop unrolling fails due to unexpected graph shape
Summary: C2 loop unrolling fails due to unexpected graph shape
Bug url: https://bugs.openjdk.java.net/browse/JDK-8148754
---
hotspot/src/share/vm/opto/loopTransform.cpp | 44 ++++++++-------------
hotspot/src/share/vm/opto/loopnode.cpp | 36 +++++++++++++++++
hotspot/src/share/vm/opto/loopnode.hpp | 3 ++
hotspot/src/share/vm/opto/superword.cpp | 18 +++------
4 files changed, 61 insertions(+), 40 deletions(-)
diff --git a/hotspot/src/share/vm/opto/loopTransform.cpp b/hotspot/src/share/vm/opto/loopTransform.cpp
index e3637b652..f6783b910 100644
--- a/hotspot/src/share/vm/opto/loopTransform.cpp
+++ b/hotspot/src/share/vm/opto/loopTransform.cpp
@@ -1222,21 +1222,14 @@ void PhaseIdealLoop::do_unroll( IdealLoopTree *loop, Node_List &old_new, bool ad
Node *opaq = NULL;
if (adjust_min_trip) { // If not maximally unrolling, need adjustment
- // Search for zero-trip guard.
- assert( loop_head->is_main_loop(), "" );
- assert( ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "" );
- Node *iff = ctrl->in(0);
- assert( iff->Opcode() == Op_If, "" );
- Node *bol = iff->in(1);
- assert( bol->Opcode() == Op_Bool, "" );
- Node *cmp = bol->in(1);
- assert( cmp->Opcode() == Op_CmpI, "" );
- opaq = cmp->in(2);
- // Occasionally it's possible for a zero-trip guard Opaque1 node to be
- // optimized away and then another round of loop opts attempted.
- // We can not optimize this particular loop in that case.
- if (opaq->Opcode() != Op_Opaque1)
- return; // Cannot find zero-trip guard! Bail out!
+ // Check the shape of the graph at the loop entry. If an inappropriate
+ // graph shape is encountered, the compiler bails out loop unrolling;
+ // compilation of the method will still succeed.
+ if (!is_canonical_main_loop_entry(loop_head)) {
+ return;
+ }
+ // get a not shared opaque' node for Zero-trip test
+ opaq = ctrl->in(0)->in(1)->in(1)->in(2);
// Zero-trip test uses an 'opaque' node which is not shared.
assert(opaq->outcnt() == 1 && opaq->in(1) == limit, "");
}
@@ -1806,7 +1799,6 @@ void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
#endif
assert(RangeCheckElimination, "");
CountedLoopNode *cl = loop->_head->as_CountedLoop();
- assert(cl->is_main_loop(), "");
// protect against stride not being a constant
if (!cl->stride_is_con())
@@ -1818,20 +1810,18 @@ void PhaseIdealLoop::do_range_check( IdealLoopTree *loop, Node_List &old_new ) {
// to not ever trip end tests
Node *main_limit = cl->limit();
+ // Check graph shape. Cannot optimize a loop if zero-trip
+ // Opaque1 node is optimized away and then another round
+ // of loop opts attempted.
+ if (!is_canonical_main_loop_entry(cl)) {
+ return;
+ }
+
// Need to find the main-loop zero-trip guard
Node *ctrl = cl->in(LoopNode::EntryControl);
- assert(ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "");
Node *iffm = ctrl->in(0);
- assert(iffm->Opcode() == Op_If, "");
- Node *bolzm = iffm->in(1);
- assert(bolzm->Opcode() == Op_Bool, "");
- Node *cmpzm = bolzm->in(1);
- assert(cmpzm->is_Cmp(), "");
- Node *opqzm = cmpzm->in(2);
- // Can not optimize a loop if zero-trip Opaque1 node is optimized
- // away and then another round of loop opts attempted.
- if (opqzm->Opcode() != Op_Opaque1)
- return;
+ // get the zero-trip Opaque1 node for testing the main limits
+ Node *opqzm = iffm->in(1)->in(1)->in(2);
assert(opqzm->in(1) == main_limit, "do not understand situation");
// Find the pre-loop limit; we will expand it's iterations to
diff --git a/hotspot/src/share/vm/opto/loopnode.cpp b/hotspot/src/share/vm/opto/loopnode.cpp
index 37c56681d..e2c0645cf 100644
--- a/hotspot/src/share/vm/opto/loopnode.cpp
+++ b/hotspot/src/share/vm/opto/loopnode.cpp
@@ -3284,6 +3284,42 @@ Node* PhaseIdealLoop::compute_lca_of_uses(Node* n, Node* early, bool verify) {
return LCA;
}
+// Check the shape of the graph at the loop entry. In some cases,
+// the shape of the graph does not match the shape outlined below.
+// That is caused by the Opaque1 node "protecting" the shape of
+// the graph being removed by, for example, the IGVN performed
+// in PhaseIdealLoop::build_and_optimize().
+//
+// After the Opaque1 node has been removed, optimizations (e.g., split-if,
+// loop unswitching, and IGVN, or a combination of them) can freely change
+// the graph's shape. As a result, the graph shape outlined below cannot
+// be guaranteed anymore.
+bool PhaseIdealLoop::is_canonical_main_loop_entry(CountedLoopNode* cl) {
+ assert(cl->is_main_loop(), "check should be applied to main loops");
+ Node* ctrl = cl->in(LoopNode::EntryControl);
+ if (ctrl == NULL || (!ctrl->is_IfTrue() && !ctrl->is_IfFalse())) {
+ return false;
+ }
+ Node* iffm = ctrl->in(0);
+ if (iffm == NULL || !iffm->is_If()) {
+ return false;
+ }
+ Node* bolzm = iffm->in(1);
+ if (bolzm == NULL || !bolzm->is_Bool()) {
+ return false;
+ }
+ Node* cmpzm = bolzm->in(1);
+ if (cmpzm == NULL || !cmpzm->is_Cmp()) {
+ return false;
+ }
+ // get the compare node, if null or not return false
+ Node* opqzm = cmpzm->in(2);
+ if (opqzm == NULL || opqzm->Opcode() != Op_Opaque1) {
+ return false;
+ }
+ return true;
+}
+
//------------------------------get_late_ctrl----------------------------------
// Compute latest legal control.
Node *PhaseIdealLoop::get_late_ctrl( Node *n, Node *early ) {
diff --git a/hotspot/src/share/vm/opto/loopnode.hpp b/hotspot/src/share/vm/opto/loopnode.hpp
index 150d1be0f..558b10504 100644
--- a/hotspot/src/share/vm/opto/loopnode.hpp
+++ b/hotspot/src/share/vm/opto/loopnode.hpp
@@ -621,6 +621,9 @@ private:
bool cast_incr_before_loop(Node* incr, Node* ctrl, Node* loop);
public:
+
+ static bool is_canonical_main_loop_entry(CountedLoopNode* cl);
+
bool has_node( Node* n ) const {
guarantee(n != NULL, "No Node.");
return _nodes[n->_idx] != NULL;
diff --git a/hotspot/src/share/vm/opto/superword.cpp b/hotspot/src/share/vm/opto/superword.cpp
index 0bc171b5c..a14210ee2 100644
--- a/hotspot/src/share/vm/opto/superword.cpp
+++ b/hotspot/src/share/vm/opto/superword.cpp
@@ -2209,21 +2209,13 @@ void SuperWord::align_initial_loop_index(MemNode* align_to_ref) {
//----------------------------get_pre_loop_end---------------------------
// Find pre loop end from main loop. Returns null if none.
CountedLoopEndNode* SuperWord::get_pre_loop_end(CountedLoopNode* cl) {
- Node* ctrl = cl->in(LoopNode::EntryControl);
- if (!ctrl->is_IfTrue() && !ctrl->is_IfFalse()) return NULL;
- Node* iffm = ctrl->in(0);
- if (!iffm->is_If()) return NULL;
- Node* bolzm = iffm->in(1);
- if (!bolzm->is_Bool()) return NULL;
- Node* cmpzm = bolzm->in(1);
- if (!cmpzm->is_Cmp()) return NULL;
- Node* opqzm = cmpzm->in(2);
- // Can not optimize a loop if zero-trip Opaque1 node is optimized
- // away and then another round of loop opts attempted.
- if (opqzm->Opcode() != Op_Opaque1) {
+ // The loop cannot be optimized if the graph shape at
+ // the loop entry is inappropriate.
+ if (!PhaseIdealLoop::is_canonical_main_loop_entry(cl)) {
return NULL;
}
- Node* p_f = iffm->in(0);
+
+ Node* p_f = cl->in(LoopNode::EntryControl)->in(0)->in(0);
if (!p_f->is_IfFalse()) return NULL;
if (!p_f->in(0)->is_CountedLoopEnd()) return NULL;
CountedLoopEndNode* pre_end = p_f->in(0)->as_CountedLoopEnd();
--
2.19.0
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