make memdep use the getModRefInfo method for stores instead of the

low-level alias() method, allowing it to reason more aggressively
about pointers into constant memory.  PR4189


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72403 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/GVN/load-constant-mem.ll

@@ -0,0 +1,13 @@
+; RUN: llvm-as < %s | opt -gvn -instcombine | llvm-dis | grep {ret i32 0}
+; PR4189
+@G = external constant [4 x i32]
+
+define i32 @test(i8* %p, i32 %i) nounwind {
+entry:
+	%P = getelementptr [4 x i32]* @G, i32 0, i32 %i
+	%A = load i32* %P
+	store i8 4, i8* %p
+	%B = load i32* %P
+	%C = sub i32 %A, %B
+	ret i32 %C
+}