Cleanup patch:

Semantics of parameters named Index and Idx were inconsistent between
"include/llvm/IR/Attributes.h", "lib/IR/AttributeImpl.h" and
"lib/IR/Attributes.cpp": sometimes these were fixed 1-based indexes of IR
parameters (or AttributeSet::ReturnIndex for IR return values or
AttributeSet::FunctionIndex for IR functions), other times they were the
internal slot for storage in the underlying AttributeSetImpl. I renamed usage of
the former to "Index" and usage of the latter to "Slot" ("Slot" was already
being used consistently for the latter in a subset of cases)

Patch by Stephen Lin!

llvm-svn: 179791
diff --git a/llvm/lib/IR/AttributeImpl.h b/llvm/lib/IR/AttributeImpl.h
index 7d34c72..b17aa43 100644
--- a/llvm/lib/IR/AttributeImpl.h
+++ b/llvm/lib/IR/AttributeImpl.h
@@ -248,15 +248,15 @@
   typedef AttributeSetNode::iterator       iterator;
   typedef AttributeSetNode::const_iterator const_iterator;
 
-  iterator begin(unsigned Idx)
-    { return AttrNodes[Idx].second->begin(); }
-  iterator end(unsigned Idx)
-    { return AttrNodes[Idx].second->end(); }
+  iterator begin(unsigned Slot)
+    { return AttrNodes[Slot].second->begin(); }
+  iterator end(unsigned Slot)
+    { return AttrNodes[Slot].second->end(); }
 
-  const_iterator begin(unsigned Idx) const
-    { return AttrNodes[Idx].second->begin(); }
-  const_iterator end(unsigned Idx) const
-    { return AttrNodes[Idx].second->end(); }
+  const_iterator begin(unsigned Slot) const
+    { return AttrNodes[Slot].second->begin(); }
+  const_iterator end(unsigned Slot) const
+    { return AttrNodes[Slot].second->end(); }
 
   void Profile(FoldingSetNodeID &ID) const {
     Profile(ID, AttrNodes);