rs6000 fused multiply-add patch [+ patchlet]

[Richard Kenner]

    Reducing the amount of rtl isn't the same as improving performance.

No, but unless the MD file has a serious problem, it is *one way* of
improving performance.

    The only difference in this regard is that the original combine
    is easier to prove to be terminating.

And that it sticks to the semantics, which is *combining* insns.

There's no question that we don't current have a pass which is good at
finding the simplest form of the RTL.  The idea is to move as much of
combine as possible into simplify-rtx.c.  Then combine is very small and
other passes will do what you are trying to do.