[llvm-commits] [llvm] r132611 - in /llvm/trunk: lib/Analysis/BasicAliasAnalysis.cpp test/Analysis/BasicAA/2010-09-15-GEP-SignedArithmetic.ll test/Analysis/TypeBasedAliasAnalysis/dynamic-indices.ll

[Dan Gohman]

Author: djg
Date: Fri Jun  3 19:46:31 2011
New Revision: 132611

URL: http://llvm.org/viewvc/llvm-project?rev=132611&view=rev
Log:
Reapply r131781 (revert r131809), now that some BasicAA shortcomings
it exposed are fixed.

Added:
    llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/dynamic-indices.ll
      - copied unchanged from r131808, llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/dynamic-indices.ll
Modified:
    llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
    llvm/trunk/test/Analysis/BasicAA/2010-09-15-GEP-SignedArithmetic.ll

Modified: llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=132611&r1=132610&r2=132611&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Fri Jun  3 19:46:31 2011
@@ -944,7 +944,17 @@
       return NoAlias;
   }
   
-  return MayAlias;
+  // 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;
 }
 
 static AliasAnalysis::AliasResult

Modified: llvm/trunk/test/Analysis/BasicAA/2010-09-15-GEP-SignedArithmetic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/2010-09-15-GEP-SignedArithmetic.ll?rev=132611&r1=132610&r2=132611&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/BasicAA/2010-09-15-GEP-SignedArithmetic.ll (original)
+++ llvm/trunk/test/Analysis/BasicAA/2010-09-15-GEP-SignedArithmetic.ll Fri Jun  3 19:46:31 2011
@@ -1,4 +1,4 @@
-; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output |& grep {1 may alias}
+; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output |& grep {1 partial alias}
 ; PR7959
 
 target datalayout = "e-p:32:32:32"