Here's an updated patch to add more type narrowing to match.pd.

Changes since the last version:

Slight refactoring of the condition by using types_match as suggested by 
Richi.  I also applied the new types_match to 2 other patterns in 
match.pd where it seemed clearly appropriate.

Additionally the transformation is restricted by using the new 
single_use predicate.  I didn't change other patterns in match.pd to use 
the new single_use predicate.  But some probably could be changed.

This (of course) continues to pass the bootstrap and regression check 
for x86-linux-gnu.

There's still a ton of work to do in this space.  This is meant to be an 
incremental stand-alone improvement.

OK now?



Jeff