[PATCH] D93810: [RS4GC] Lazily set changed flag when folding single entry phis

[Yevgeny Rouban via Phabricator via llvm-commits]

yrouban created this revision.
yrouban added reviewers: apilipenko, reames.
Herald added subscribers: dantrushin, hiraditya.
yrouban requested review of this revision.
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Herald added a subscriber: llvm-commits.

The function //FoldSingleEntryPHINodes()// is changed to return if it has changed IR or not. This return value is used by RS4GC to set the //MadeChange// flag respectively.
The change is simple. No test is needed.


https://reviews.llvm.org/D93810

Files:
  llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
  llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
  llvm/lib/Transforms/Utils/BasicBlockUtils.cpp


Index: llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
===================================================================
--- llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -136,9 +136,10 @@
   return !DeadBlocks.empty();
 }
 
-void llvm::FoldSingleEntryPHINodes(BasicBlock *BB,
+bool llvm::FoldSingleEntryPHINodes(BasicBlock *BB,
                                    MemoryDependenceResults *MemDep) {
-  if (!isa<PHINode>(BB->begin())) return;
+  if (!isa<PHINode>(BB->begin()))
+    return false;
 
   while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
     if (PN->getIncomingValue(0) != PN)
@@ -151,6 +152,7 @@
 
     PN->eraseFromParent();
   }
+  return true;
 }
 
 bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI,
Index: llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
+++ llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
@@ -2736,10 +2736,8 @@
   // of liveness sets for no good reason.  It may be harder to do this post
   // insertion since relocations and base phis can confuse things.
   for (BasicBlock &BB : F)
-    if (BB.getUniquePredecessor()) {
-      MadeChange = true;
-      FoldSingleEntryPHINodes(&BB);
-    }
+    if (BB.getUniquePredecessor())
+      MadeChange |= FoldSingleEntryPHINodes(&BB);
 
   // Before we start introducing relocations, we want to tweak the IR a bit to
   // avoid unfortunate code generation effects.  The main example is that we
Index: llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
===================================================================
--- llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -74,7 +74,7 @@
 /// in it, fold them away. This handles the case when all entries to the PHI
 /// nodes in a block are guaranteed equal, such as when the block has exactly
 /// one predecessor.
-void FoldSingleEntryPHINodes(BasicBlock *BB,
+bool FoldSingleEntryPHINodes(BasicBlock *BB,
                              MemoryDependenceResults *MemDep = nullptr);
 
 /// Examine each PHI in the given block and delete it if it is dead. Also


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