Add an enum for the return and function indexes into the AttrListPtr object. This gets rid of some magic numbers.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165924 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/IPO/FunctionAttrs.cpp b/lib/Transforms/IPO/FunctionAttrs.cpp
index ba24770..9fe42f0 100644
--- a/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -215,12 +215,14 @@
     Attributes::Builder B;
     B.addAttribute(Attributes::ReadOnly)
       .addAttribute(Attributes::ReadNone);
-    F->removeAttribute(~0, Attributes::get(F->getContext(), B));
+    F->removeAttribute(AttrListPtr::FunctionIndex,
+                       Attributes::get(F->getContext(), B));
 
     // Add in the new attribute.
     B.clear();
     B.addAttribute(ReadsMemory ? Attributes::ReadOnly : Attributes::ReadNone);
-    F->addAttribute(~0, Attributes::get(F->getContext(), B));
+    F->addAttribute(AttrListPtr::FunctionIndex,
+                    Attributes::get(F->getContext(), B));
 
     if (ReadsMemory)
       ++NumReadOnly;