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Re: rs6000 fused multiply-add patch [+ patchlet]
- From: David Edelsohn <dje at watson dot ibm dot com>
- To: Segher Boessenkool <segher at koffie dot nl>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Mon, 30 Dec 2002 23:51:33 -0500
- Subject: Re: rs6000 fused multiply-add patch [+ patchlet]
- References: <3E111A25.816F2D1E@koffie.nl>
The combine pass is called "combine" because it is predicated on
combining instructions and uses decreased instructions as the goal. If
more optimal instruction sequences should be used, that needs to be
optimized by a different pass. Your bitfield+mfcr -> logic instruction
example might be appropriate as define_peephole2 patterns. Your load+mask
-> narrower load already should be handled correctly by other
optimizations or the combiner because it seem like it should decrease the
number of instructions. If the code size is decreasing then the number of
instructions is decreasing, so maybe we need to add patterns transforming
three instructions into two instructions.
David