[llvm] 5e855f1 - [MemCpyOpt] Don't hoist store that's not guaranteed to execute

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2020-10-10T10:26:28+02:00
New Revision: 5e855f1e8056ca0800134469ee82e0ff5ad5af59

URL: https://github.com/llvm/llvm-project/commit/5e855f1e8056ca0800134469ee82e0ff5ad5af59
DIFF: https://github.com/llvm/llvm-project/commit/5e855f1e8056ca0800134469ee82e0ff5ad5af59.diff

LOG: [MemCpyOpt] Don't hoist store that's not guaranteed to execute

MemCpyOpt can hoist stores while load+store pairs into memcpy.
This hoisting can currently result in stores being executed that
weren't guaranteed to execute in the original problem.

Differential Revision: https://reviews.llvm.org/D89154

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
    llvm/test/Transforms/MemCpyOpt/fca2memcpy.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 64821c70217b..c7bdf860f14b 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -491,6 +491,11 @@ bool MemCpyOptPass::moveUp(StoreInst *SI, Instruction *P, const LoadInst *LI) {
   for (auto I = --SI->getIterator(), E = P->getIterator(); I != E; --I) {
     auto *C = &*I;
 
+    // Make sure hoisting does not perform a store that was not guaranteed to
+    // happen.
+    if (!isGuaranteedToTransferExecutionToSuccessor(C))
+      return false;
+
     bool MayAlias = isModOrRefSet(AA->getModRefInfo(C, None));
 
     bool NeedLift = false;

diff  --git a/llvm/test/Transforms/MemCpyOpt/fca2memcpy.ll b/llvm/test/Transforms/MemCpyOpt/fca2memcpy.ll
index 6cffce50eb80..d97c6fa39d86 100644
--- a/llvm/test/Transforms/MemCpyOpt/fca2memcpy.ll
+++ b/llvm/test/Transforms/MemCpyOpt/fca2memcpy.ll
@@ -147,12 +147,11 @@ define void @noaliasaddrproducer(%S* %src, %S* noalias %dst, i32* noalias %dstid
 
 define void @throwing_call(%S* noalias %src, %S* %dst) {
 ; CHECK-LABEL: @throwing_call(
-; CHECK-NEXT:    [[TMP1:%.*]] = bitcast %S* [[SRC:%.*]] to i8*
-; CHECK-NEXT:    [[TMP2:%.*]] = bitcast %S* [[DST:%.*]] to i8*
-; CHECK-NEXT:    [[TMP3:%.*]] = bitcast %S* [[SRC]] to i8*
-; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 8 [[TMP2]], i8* align 8 [[TMP3]], i64 16, i1 false)
-; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* align 8 [[TMP1]], i8 0, i64 16, i1 false)
+; CHECK-NEXT:    [[TMP1:%.*]] = load [[S:%.*]], %S* [[SRC:%.*]], align 8
+; CHECK-NEXT:    [[TMP2:%.*]] = bitcast %S* [[SRC]] to i8*
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* align 8 [[TMP2]], i8 0, i64 16, i1 false)
 ; CHECK-NEXT:    call void @call() [[ATTR2:#.*]]
+; CHECK-NEXT:    store [[S]] [[TMP1]], %S* [[DST:%.*]], align 8
 ; CHECK-NEXT:    ret void
 ;
   %1 = load %S, %S* %src