Allow basicaa to walk through geps with identical indices in

parallel, allowing it to decide that P/Q must alias if A/B
must alias in things like:
 P = gep A, 0, i, 1
 Q = gep B, 0, i, 1

This allows GVN to delete 62 more instructions out of 403.gcc.

llvm-svn: 60820

1 files changed, 16 insertions, 0 deletions

diff --git a/llvm/test/Analysis/BasicAA/2008-12-09-GEP-IndicesAlias.ll b/llvm/test/Analysis/BasicAA/2008-12-09-GEP-IndicesAlias.ll
new file mode 100644
index 00000000000..967a36edcb3
--- /dev/null
+++ b/llvm/test/Analysis/BasicAA/2008-12-09-GEP-IndicesAlias.ll
@@ -0,0 +1,16 @@
+; RUN: llvm-as < %s | opt -aa-eval -print-all-alias-modref-info -disable-output |& grep {MustAlias:.*%R,.*%r}
+; Make sure that basicaa thinks R and r are must aliases.
+
+define i32 @test(i8 * %P) {
+entry:
+	%Q = bitcast i8* %P to {i32, i32}*
+	%R = getelementptr {i32, i32}* %Q, i32 0, i32 1
+	%S = load i32* %R
+
+	%q = bitcast i8* %P to {i32, i32}*
+	%r = getelementptr {i32, i32}* %q, i32 0, i32 1
+	%s = load i32* %r
+
+	%t = sub i32 %S, %s
+	ret i32 %t
+}