enhance basicaa to return "Mod" for a memcpy call when the

queried location doesn't overlap the source, and add a testcase.

llvm-svn: 120370

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 3e634240901..74bee947a3d 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -687,10 +687,15 @@ BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
         Len = LenCI->getZExtValue();
       Value *Dest = II->getArgOperand(0);
       Value *Src = II->getArgOperand(1);
+      // If it can't overlap the source dest, then it doesn't modref the loc.
       if (isNoAlias(Location(Dest, Len), Loc)) {
         if (isNoAlias(Location(Src, Len), Loc))
           return NoModRef;
+        // If it can't overlap the dest, then worst case it reads the loc.
         Min = Ref;
+      } else if (isNoAlias(Location(Src, Len), Loc)) {
+        // If it can't overlap the source, then worst case it mutates the loc.
+        Min = Mod;
       }
       break;
     }