Revert commit 131781, to see if it fixes the x86-64 dragonegg buildbot.

Original log message:
When BasicAA can determine that two pointers have the same base but
differ by a dynamic offset, return PartialAlias instead of MayAlias.
See the comment in the code for details. This fixes PR9971.

llvm-svn: 131809

1 files changed, 1 insertions, 11 deletions

diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index f50660844fe..f1bb8a38f09 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -940,17 +940,7 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
       return NoAlias;
   }
   
-  // Statically, we can see that the base objects are the same, but the
-  // pointers have dynamic offsets which we can't resolve. And none of our
-  // little tricks above worked.
-  //
-  // TODO: Returning PartialAlias instead of MayAlias is a mild hack; the
-  // practical effect of this is protecting TBAA in the case of dynamic
-  // indices into arrays of unions. An alternative way to solve this would
-  // be to have clang emit extra metadata for unions and/or union accesses.
-  // A union-specific solution wouldn't handle the problem for malloc'd
-  // memory however.
-  return PartialAlias;
+  return MayAlias;
 }
 
 /// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select