Another BasicAA fix. If a value does not alias a GEP's base pointer, then it

cannot alias the GEP. GEP pointer alias rule states this clearly:
A pointer value formed from a getelementptr instruction is associated with the
addresses associated with the first operand of the getelementptr.

llvm-svn: 84079

1 files changed, 30 insertions, 0 deletions

diff --git a/llvm/test/Analysis/BasicAA/2009-10-13-GEP-BaseNoAlias.ll b/llvm/test/Analysis/BasicAA/2009-10-13-GEP-BaseNoAlias.ll
new file mode 100644
index 00000000000..771636f42cf
--- /dev/null
+++ b/llvm/test/Analysis/BasicAA/2009-10-13-GEP-BaseNoAlias.ll
@@ -0,0 +1,30 @@
+; RUN: opt < %s -aa-eval -print-all-alias-modref-info -disable-output |& grep {NoAlias:.*%P,.*@Z}
+; If GEP base doesn't alias Z, then GEP doesn't alias Z.
+; rdar://7282591
+
+@Y = common global i32 0
+@Z = common global i32 0
+
+define void @foo(i32 %cond) nounwind ssp {
+entry:
+  %a = alloca i32
+  %tmp = icmp ne i32 %cond, 0
+  br i1 %tmp, label %bb, label %bb1
+
+bb:
+  %b = getelementptr i32* %a, i32 0
+  br label %bb2
+
+bb1:
+  br label %bb2
+
+bb2:
+  %P = phi i32* [ %b, %bb ], [ @Y, %bb1 ]
+  %tmp1 = load i32* @Z, align 4
+  store i32 123, i32* %P, align 4
+  %tmp2 = load i32* @Z, align 4
+  br label %return
+
+return:
+  ret void
+}