[GlobalsAA] Relax condition in checking globals as args to functions

Summary:
Since globals may escape as function arguments (even when they have been 
found to be non-escaping, because of optimizations such as memcpyoptimizer
that replaces stores with memcpy), all arguments to a function are checked
during query to make sure they are identifiable. At that time, also ensure
we return a conservative result only if the arguments don't alias to our global.

Reviewers: hfinkel, jmolloy

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D16140

llvm-svn: 257750

1 files changed, 5 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/GlobalsModRef.cpp b/llvm/lib/Analysis/GlobalsModRef.cpp
index 1babb822074..425d9de876b 100644
--- a/llvm/lib/Analysis/GlobalsModRef.cpp
+++ b/llvm/lib/Analysis/GlobalsModRef.cpp
@@ -863,7 +863,11 @@ ModRefInfo GlobalsAAResult::getModRefInfoForArgument(ImmutableCallSite CS,
     GetUnderlyingObjects(A, Objects, DL);
     
     // All objects must be identified.
-    if (!std::all_of(Objects.begin(), Objects.end(), isIdentifiedObject))
+    if (!std::all_of(Objects.begin(), Objects.end(), isIdentifiedObject) &&
+        // Try ::alias to see if all objects are known not to alias GV.
+        !std::all_of(Objects.begin(), Objects.end(), [&](Value *V) {
+          return this->alias(MemoryLocation(V), MemoryLocation(GV)) == NoAlias;
+          }))
       return ConservativeResult;
 
     if (std::find(Objects.begin(), Objects.end(), GV) != Objects.end())