[PATCH] Refactor and enhance FMA combine

[Owen Anderson]

> On Apr 2, 2015, at 1:08 PM, Mehdi Amini <mehdi.amini at apple.com> wrote:
> 
> I’m not sure backend specific transform can rely on the generic LLVM combiner not to canonicalize in a way that they “don’t like”. I think they have to handle the canonical form whatever it is. 
> I suspect that many canonicalizations in general can go in the wrong direction in specific cases for specific targets.

This is true, but it’s also worthwhile to consider ramifications for targets when choosing a canonical form.  It’s generally not a good idea to pick a canonical representation that is the opposite of what every backend wants.  In this case, it might not be every backend, but it does seem like there’s a class of processors for which this might not be desirable, and it’s worth considering that when choosing which form to consider canonical.  I’m not interested in dictating the outcome of that consideration, but it’s still a consideration to be made.

—Owen
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