add a missed optimization

llvm-svn: 25786

llvm/lib/Target/X86/README.txt

@@ -204,3 +204,13 @@ There are two ways to fix this:
    disambiguate the pointers.
 
 Number 1 is the preferred solution.
+
+//===---------------------------------------------------------------------===//
+
+The instruction selector sometimes misses folding a load into a compare.  The
+pattern is written as (cmp reg, (load p)).  Because the compare isn't 
+commutative, it is not matched with the load on both sides.  The dag combiner
+should be made smart enough to cannonicalize the load into the RHS of a compare
+when it can invert the result of the compare for free.
+
+