Commit 6291b0d9 authored by Hans Wennborg's avatar Hans Wennborg
Browse files

Merging r323759: 

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r323759 | spatel | 2018-01-30 14:53:59 +0100 (Tue, 30 Jan 2018) | 10 lines

[DSE] make sure memory is not modified before partial store merging (PR36129)

We missed a critical check in D30703. We must make sure that no intermediate 
store is sitting between the stores that we want to merge.

This should fix:
https://bugs.llvm.org/show_bug.cgi?id=36129

Differential Revision: https://reviews.llvm.org/D42663

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llvm-svn: 324086
parent 7a8cd3ec

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

+2 −1
Original line number Diff line number Diff line
@@ -1176,7 +1176,8 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA, 
          auto *Earlier = dyn_cast<StoreInst>(DepWrite);

          auto *Later = dyn_cast<StoreInst>(Inst);

          if (Earlier && isa<ConstantInt>(Earlier->getValueOperand()) &&

              Later && isa<ConstantInt>(Later->getValueOperand())) {

              Later && isa<ConstantInt>(Later->getValueOperand()) &&

              memoryIsNotModifiedBetween(Earlier, Later, AA)) {

            // If the store we find is:

            //   a) partially overwritten by the store to 'Loc'

            //   b) the later store is fully contained in the earlier one and

llvm/test/Transforms/DeadStoreElimination/merge-stores.ll

+17 −0
Original line number Diff line number Diff line
@@ -186,6 +186,23 @@ define void @PR34074(i32* %x, i64* %y) { 
  ret void

}



; We can't eliminate the last store because P and Q may alias.



define void @PR36129(i32* %P, i32* %Q) {

; CHECK-LABEL: @PR36129(

; CHECK-NEXT:    store i32 1, i32* [[P:%.*]]

; CHECK-NEXT:    [[P2:%.*]] = bitcast i32* [[P]] to i8*

; CHECK-NEXT:    store i32 2, i32* [[Q:%.*]]

; CHECK-NEXT:    store i8 3, i8* [[P2]]

; CHECK-NEXT:    ret void

;

  store i32 1, i32* %P

  %P2 = bitcast i32* %P to i8*

  store i32 2, i32* %Q

  store i8 3, i8* %P2

  ret void

}



!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 5.0.0 (trunk 306512)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)

!1 = !DIFile(filename: "me.cpp", directory: "/compiler-explorer")

!2 = !{}