Teach BasicAliasAnalysis to understand constant gep indices that fall

beyond their associated static array type.

I believe that this fixes a legitimate bug, because BasicAliasAnalysis
already has code to check for this condition that works for non-constant
indices, however it was missing the case of constant indices. With this
change, it checks for both.

This fixes PR4267, and miscompiles of SPEC 188.ammp and 464.h264.href.

llvm-svn: 72451

1 files changed, 27 insertions, 0 deletions

diff --git a/llvm/test/Analysis/BasicAA/constant-over-index.ll b/llvm/test/Analysis/BasicAA/constant-over-index.ll
new file mode 100644
index 00000000000..e92995be5e6
--- /dev/null
+++ b/llvm/test/Analysis/BasicAA/constant-over-index.ll
@@ -0,0 +1,27 @@
+; RUN: llvm-as < %s | opt -aa-eval -print-all-alias-modref-info \
+; RUN:   |& grep {MayAlias:	double\\* \[%\]p.0.i.0, double\\* \[%\]p3\$}
+; PR4267
+
+; %p3 is equal to %p.0.i.0 on the second iteration of the loop,
+; so MayAlias is needed.
+
+define void @foo([3 x [3 x double]]* noalias %p) {
+entry:
+  %p3 = getelementptr [3 x [3 x double]]* %p, i64 0, i64 0, i64 3
+  br label %loop
+
+loop:
+  %i = phi i64 [ 0, %entry ], [ %i.next, %loop ]
+
+  %p.0.i.0 = getelementptr [3 x [3 x double]]* %p, i64 0, i64 %i, i64 0
+
+  volatile store double 0.0, double* %p3
+  volatile store double 0.1, double* %p.0.i.0
+
+  %i.next = add i64 %i, 1
+  %cmp = icmp slt i64 %i.next, 3
+  br i1 %cmp, label %loop, label %exit
+
+exit:
+  ret void
+}