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, 5 insertions, 0 deletions

diff --git a/include/llvm/Analysis/AliasAnalysis.h b/include/llvm/Analysis/AliasAnalysis.h
index 7d5c5fc99b..167371b6b2 100644
--- a/include/llvm/Analysis/AliasAnalysis.h
+++ b/include/llvm/Analysis/AliasAnalysis.h
@@ -188,6 +188,11 @@ public:
     return alias(LocA, LocB) == MustAlias;
   }
 
+  /// isMustAlias - A convenience wrapper.
+  bool isMustAlias(const Value *V1, const Value *V2) {
+    return alias(V1, 1, V2, 1) == MustAlias;
+  }
+  
   /// pointsToConstantMemory - If the specified memory location is
   /// known to be constant, return true. If OrLocal is true and the
   /// specified memory location is known to be "local" (derived from