Default-addressspace null pointers don't alias anything. This allows

GVN to be more aggressive. Patch by Hans Wennborg! (with a comment added by me)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86582 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/GVN/null-aliases-nothing.ll

@@ -0,0 +1,20 @@
+; RUN: opt %s -gvn -S | FileCheck %s
+
+%t = type { i32 }
+declare void @test1f(i8*)
+
+define void @test1(%t* noalias %stuff ) {
+    %p = getelementptr inbounds %t* %stuff, i32 0, i32 0
+    %before = load i32* %p
+
+    call void @test1f(i8* null)
+
+    %after = load i32* %p ; <--- This should be a dead load
+    %sum = add i32 %before, %after;
+
+    store i32 %sum, i32* %p
+    ret void
+; CHECK: load
+; CHECK-NOT: load
+; CHECK: ret void
+}