Teach BasicAA that a constant expression can't alias memory provably not

allocated until runtime (such as an alloca). Patch by Hans Wennborg!

llvm-svn: 88760

1 files changed, 39 insertions, 0 deletions

diff --git a/llvm/test/Transforms/DeadStoreElimination/const-pointers.ll b/llvm/test/Transforms/DeadStoreElimination/const-pointers.ll
new file mode 100644
index 00000000000..ce18c6fb819
--- /dev/null
+++ b/llvm/test/Transforms/DeadStoreElimination/const-pointers.ll
@@ -0,0 +1,39 @@
+; RUN: opt %s -dse -S | FileCheck %s
+
+%t = type { i32 }
+
+@g = global i32 42;
+
+define void @test1(%t* noalias %pp) {
+  %p = getelementptr inbounds %t* %pp, i32 0, i32 0
+
+  store i32 1, i32* %p; <-- This is dead
+  %x = load i32* inttoptr (i32 12345 to i32*)
+  store i32 %x, i32* %p
+  ret void
+; CHECK define void @test1
+; CHECK: store
+; CHECK-NOT: store
+; CHECK: ret void
+}
+
+define void @test3() {
+  store i32 1, i32* @g; <-- This is dead.
+  store i32 42, i32* @g
+  ret void
+;CHECK define void @test3
+;CHECK: store
+;CHECK-NOT: store
+;CHECK: ret void
+}
+
+define void @test4(i32* %p) {
+  store i32 1, i32* %p
+  %x = load i32* @g; <-- %p and @g could alias
+  store i32 %x, i32* %p
+  ret void
+; CHECK define void @test4
+; CHECK: store
+; CHECK: store
+; CHECK: ret void
+}