GlobalsAA: Functions with the argmemonly attribute won't read arbitrary globals

Summary:
In preparation for changing GlobalsAA to stop assuming that intrinsics
can't read arbitrary globals, we need to make sure GlobalsAA is querying
function attributes rather than relying on this assumption.

This patch was inspired by: http://reviews.llvm.org/D20206

Reviewers: jmolloy, hfinkel

Subscribers: eli.friedman, llvm-commits

Differential Revision: https://reviews.llvm.org/D21318

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275433 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/GlobalsModRef.cpp

@@ -498,7 +498,7 @@ void GlobalsAAResult::AnalyzeCallGraph(CallGraph &CG, Module &M) {
           // Can't do better than that!
         } else if (F->onlyReadsMemory()) {
           FI.addModRefInfo(MRI_Ref);
-          if (!F->isIntrinsic())
+          if (!F->isIntrinsic() && !F->onlyAccessesArgMemory())
             // This function might call back into the module and read a global -
             // consider every global as possibly being read by this function.
             FI.setMayReadAnyGlobal();

test/Analysis/GlobalsModRef/func-memattributes.ll

@@ -0,0 +1,31 @@
+; RUN: opt < %s -disable-basicaa -globals-aa -dse -S | FileCheck %s
+
+@X = internal global i32 4
+
+define void @test0() {
+; CHECK-LABEL: @test0
+; CHECK: store i32 0, i32* @X
+; CHECK-NEXT: call void @func_readonly() #0
+; CHECK-NEXT: store i32 1, i32* @X
+  store i32 0, i32* @X
+  call void @func_readonly() #0
+  store i32 1, i32* @X
+  ret void
+}
+
+define void @test1() {
+; CHECK-LABEL: @test1
+; CHECK-NOT: store
+; CHECK: call void @func_read_argmem_only() #1
+; CHECK-NEXT: store i32 3, i32* @X
+  store i32 2, i32* @X
+  call void @func_read_argmem_only() #1
+  store i32 3, i32* @X
+  ret void
+}
+
+declare void @func_readonly() #0
+declare void @func_read_argmem_only() #1
+
+attributes #0 = { readonly }
+attributes #1 = { readonly argmemonly }