[PATCH] Remove conflicting attributes before adding deduced readonly/readnone

[Björn Steinbrink]

Hi nlewycky,

In case of functions that have a pointer argument and only pass it to
each other, the function attributes pass deduces that the pointer should
get the readnone attribute, but fails to remove a readonly attribute
that may already have been present.

http://reviews.llvm.org/D9995

Files:
  lib/Transforms/IPO/FunctionAttrs.cpp
  test/Transforms/FunctionAttrs/readnone.ll

Index: lib/Transforms/IPO/FunctionAttrs.cpp
===================================================================
--- lib/Transforms/IPO/FunctionAttrs.cpp
+++ lib/Transforms/IPO/FunctionAttrs.cpp
@@ -703,10 +703,14 @@
     }
 
     if (ReadAttr != Attribute::None) {
-      AttrBuilder B;
+      AttrBuilder B, R;
       B.addAttribute(ReadAttr);
+      R.addAttribute(Attribute::ReadOnly)
+        .addAttribute(Attribute::ReadNone);
       for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
         Argument *A = ArgumentSCC[i]->Definition;
+        // Clear out any existing attributes.
+        A->removeAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, R));
         A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
         ReadAttr == Attribute::ReadOnly ? ++NumReadOnlyArg : ++NumReadNoneArg;
         Changed = true;
Index: test/Transforms/FunctionAttrs/readnone.ll
===================================================================
--- /dev/null
+++ test/Transforms/FunctionAttrs/readnone.ll
@@ -0,0 +1,13 @@
+; RUN: opt < %s -functionattrs -S | FileCheck %s
+
+; CHECK: define void @bar(i8* nocapture readnone)
+define void @bar(i8* readonly) {
+  call void @foo(i8* %0)
+    ret void
+}
+
+; CHECK: define void @foo(i8* nocapture readnone)
+define void @foo(i8* readonly) {
+  call void @bar(i8* %0)
+  ret void
+}

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