Fix PR8728, a miscompilation I recently introduced. When optimizing

memcpy's like:
  memcpy(A, B)
  memcpy(A, C)

we cannot delete the first memcpy as dead if A and C might be aliases.
If so, we actually get:

  memcpy(A, B)
  memcpy(A, A)

which is not correct to transform into:

  memcpy(A, A)

This patch was heavily influenced by Jakub Staszak's patch in PR8728, thanks
Jakub!



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120974 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 15 insertions, 1 deletions

diff --git a/test/Transforms/DeadStoreElimination/simple.ll b/test/Transforms/DeadStoreElimination/simple.ll
index 203cf37193..a61eac9729 100644
--- a/test/Transforms/DeadStoreElimination/simple.ll
+++ b/test/Transforms/DeadStoreElimination/simple.ll
@@ -203,7 +203,7 @@ define void @test16(i8* %P, i8* %Q) nounwind ssp {
 }
 
 ;; Overwrite of memset by memcpy.
-define void @test17(i8* %P, i8* %Q) nounwind ssp {
+define void @test17(i8* %P, i8* noalias %Q) nounwind ssp {
   tail call void @llvm.memset.i64(i8* %P, i8 42, i64 8, i32 1)
   tail call void @llvm.memcpy.i64(i8* %P, i8* %Q, i64 12, i32 1)
   ret void
@@ -222,3 +222,17 @@ define void @test17v(i8* %P, i8* %Q) nounwind ssp {
 ; CHECK-NEXT: call void @llvm.memcpy
 ; CHECK-NEXT: ret
 }
+
+; PR8728
+; Do not delete instruction where possible situation is:
+; A = B
+; A = A
+define void @test18(i8* %P, i8* %Q, i8* %R) nounwind ssp {
+  tail call void @llvm.memcpy.i64(i8* %P, i8* %Q, i64 12, i32 1)
+  tail call void @llvm.memcpy.i64(i8* %P, i8* %R, i64 12, i32 1)
+  ret void
+; CHECK: @test18
+; CHECK-NEXT: call void @llvm.memcpy
+; CHECK-NEXT: call void @llvm.memcpy
+; CHECK-NEXT: ret
+}