[llvm] r323759 - [DSE] make sure memory is not modified before partial store merging (PR36129)

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Tue Jan 30 05:53:59 2018
New Revision: 323759

URL: http://llvm.org/viewvc/llvm-project?rev=323759&view=rev
Log:
[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

Modified:
    llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
    llvm/trunk/test/Transforms/DeadStoreElimination/merge-stores.ll

Modified: llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp?rev=323759&r1=323758&r2=323759&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Tue Jan 30 05:53:59 2018
@@ -1172,7 +1172,8 @@ static bool eliminateDeadStores(BasicBlo
           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

Modified: llvm/trunk/test/Transforms/DeadStoreElimination/merge-stores.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadStoreElimination/merge-stores.ll?rev=323759&r1=323758&r2=323759&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/DeadStoreElimination/merge-stores.ll (original)
+++ llvm/trunk/test/Transforms/DeadStoreElimination/merge-stores.ll Tue Jan 30 05:53:59 2018
@@ -186,12 +186,14 @@ define void @PR34074(i32* %x, i64* %y) {
   ret void
 }
 
-; FIXME: We can't eliminate the last store because P and Q may alias.
+; 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 3, i32* [[P:%.*]]
+; 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