[PATCH] D106591: [MergeICmps] Relax sinking check

[Nikita Popov via Phabricator via llvm-commits]

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The check for sinking instructions past the load + cmp sequence currently checks for side-effects, which includes writing to memory and unwinding. However, I don't believe we care about sinking the instructions past an unwind (as they don't have any side-effects themselves).

Noticed this will reviewing uses of mayHaveSideEffect() for an upcoming change.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D106591

Files:
  llvm/lib/Transforms/Scalar/MergeICmps.cpp
  llvm/test/Transforms/MergeICmps/X86/split-block-does-work.ll


Index: llvm/test/Transforms/MergeICmps/X86/split-block-does-work.ll
===================================================================
--- llvm/test/Transforms/MergeICmps/X86/split-block-does-work.ll
+++ llvm/test/Transforms/MergeICmps/X86/split-block-does-work.ll
@@ -3,7 +3,7 @@
 
 %S = type { i32, i32, i32, i32 }
 
-declare void @foo(...)  nounwind readnone
+declare void @foo(...) readonly
 
 ; We can split %entry and create a memcmp(16 bytes).
 define zeroext i1 @opeq1(
Index: llvm/lib/Transforms/Scalar/MergeICmps.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/MergeICmps.cpp
+++ llvm/lib/Transforms/Scalar/MergeICmps.cpp
@@ -248,9 +248,9 @@
 bool BCECmpBlock::canSinkBCECmpInst(const Instruction *Inst,
                                     DenseSet<Instruction *> &BlockInsts,
                                     AliasAnalysis &AA) const {
-  // If this instruction has side effects and its in middle of the BCE cmp block
-  // instructions, then bail for now.
-  if (Inst->mayHaveSideEffects()) {
+  // If this instruction may clobber the loads and is in middle of the BCE cmp
+  // block instructions, then bail for now.
+  if (Inst->mayWriteToMemory()) {
     // Bail if this is not a simple load or store
     if (!isSimpleLoadOrStore(Inst))
       return false;


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