Remove conflicting attributes before adding deduced readonly/readnone

Summary:
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.

Reviewers: nlewycky

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9995

llvm-svn: 238152

2 files changed, 18 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
index 0166935e722..92e384a340a 100644
--- a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -703,10 +703,14 @@ bool FunctionAttrs::AddArgumentAttrs(const CallGraphSCC &SCC) {
     }
 
     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 existing readonly/readnone 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;
diff --git a/llvm/test/Transforms/FunctionAttrs/readnone.ll b/llvm/test/Transforms/FunctionAttrs/readnone.ll
new file mode 100644
index 00000000000..eddcdd2641d
--- /dev/null
+++ b/llvm/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
+}