Fix comment about Intr*Mem properties

[nhaehnle]

Summary

Follow up to D19291: it now makes sense to use two Intr*Mem properties,
in particular IntrReadMem + IntrArgMemOnly is common.

Pointed out by Mikael Holmén.

[reames]

LGTM. FYI, comment cleanup can be done without review.

llvm/trunk/include/llvm/IR/Intrinsics.td

 include "llvm/CodeGen/ValueTypes.td"
 
 //===----------------------------------------------------------------------===//
 //  Properties we keep track of for intrinsics.
 //===----------------------------------------------------------------------===//
 
 class IntrinsicProperty;
 
-// Intr*Mem - Memory properties.  An intrinsic is allowed to have at most one of
-// these properties set.  They are listed from the most aggressive (best to use
-// if correct) to the least aggressive.  If no property is set, the worst case
+// Intr*Mem - Memory properties.  If no property is set, the worst case
 // is assumed (it may read and write any memory it can get access to and it may
 // have other side effects).
 
 // IntrNoMem - The intrinsic does not access memory or have any other side
 // effects.  It may be CSE'd deleted if dead, etc.
 def IntrNoMem : IntrinsicProperty;
 
 // IntrReadMem - This intrinsic only reads from memory. It does not write to