Make DAGCombiner's global alias analysis query more precise in the case

where both pointers have non-zero offsets.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@41491 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index fda0589a6de4de2662af49310ca00be5c9126efb..0514bc181bec0dfcd37d8e83e516931713116013 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -4606,8 +4606,9 @@ bool DAGCombiner::isAlias(SDOperand Ptr1, int64_t Size1,
 
   if (CombinerGlobalAA) {
     // Use alias analysis information.
-    int Overlap1 = Size1 + SrcValueOffset1;
-    int Overlap2 = Size2 + SrcValueOffset2;
+    int64_t MinOffset = std::min(SrcValueOffset1, SrcValueOffset2);
+    int64_t Overlap1 = Size1 + SrcValueOffset1 - MinOffset;
+    int64_t Overlap2 = Size2 + SrcValueOffset2 - MinOffset;
     AliasAnalysis::AliasResult AAResult = 
                              AA.alias(SrcValue1, Overlap1, SrcValue2, Overlap2);
     if (AAResult == AliasAnalysis::NoAlias)