Pointers to zero-sized objects don't point to overlapping objects.

llvm-svn: 100789

2 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 31a649d5cc4..cfe7a1c0ca2 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -655,6 +655,11 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize,
 AliasAnalysis::AliasResult
 BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size,
                                const Value *V2, unsigned V2Size) {
+  // If either of the memory references is empty, it doesn't matter what the
+  // pointer values are.
+  if (V1Size == 0 || V2Size == 0)
+    return NoAlias;
+
   // Strip off any casts if they exist.
   V1 = V1->stripPointerCasts();
   V2 = V2->stripPointerCasts();
diff --git a/llvm/test/Analysis/BasicAA/empty.ll b/llvm/test/Analysis/BasicAA/empty.ll
new file mode 100644
index 00000000000..689efec26ad
--- /dev/null
+++ b/llvm/test/Analysis/BasicAA/empty.ll
@@ -0,0 +1,10 @@
+; RUN: opt < %s -aa-eval -print-all-alias-modref-info -disable-output \
+; RUN:   |& grep {NoAlias:	\{\}\\* \[%\]p, \{\}\\* \[%\]q}
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+
+define void @foo({}* %p, {}* %q) {
+  store {} {}, {}* %p
+  store {} {}, {}* %q
+  ret void
+}