MemoryDependenceAnalysis attempts to find the first memory dependency for function calls.

Currently, if GetLocation reports that it did not find a valid pointer (this is the case for volatile load/stores),
we ignore the result. This patch adds code to handle the cases where we did not obtain a valid pointer.

rdar://11872864  PR12899

llvm-svn: 161802

1 files changed, 7 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index 7fb154d68a2..059e57493b9 100644
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -227,13 +227,18 @@ getCallSiteDependencyFrom(CallSite CS, bool isReadOnlyCall,
 
         // Otherwise if the two calls don't interact (e.g. InstCS is readnone)
         // keep scanning.
-        break;
+        continue;
       default:
         return MemDepResult::getClobber(Inst);
       }
     }
+
+    // If we could not obtain a pointer for the instruction and the instruction
+    // touches memory then assume that this is a dependency.
+    if (MR != AliasAnalysis::NoModRef)
+      return MemDepResult::getClobber(Inst);
   }
-  
+
   // No dependence found.  If this is the entry block of the function, it is
   // unknown, otherwise it is non-local.
   if (BB != &BB->getParent()->getEntryBlock())