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Re: IEEE 754 and fused-madd (was: Re: patch: rs6000 specific)
- From: David Edelsohn <dje at watson dot ibm dot com>
- To: lucier at math dot purdue dot edu
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Thu, 06 Dec 2001 16:41:48 -0500
- Subject: Re: IEEE 754 and fused-madd (was: Re: patch: rs6000 specific)
The PowerPC port of GCC does use FMA by default unless
-mno-fused-madd is invoked.
What Dale and others at Apple seemed to be requesting was that GCC
perform some of the -ffast-math transformations by default by using
additional combiner patterns. Their argument seems to be that use of FMA
already is non-compliant, so anything is fair game.
I believe that if GCC normally only performs those transformations
with -ffast-math, then both the transformations should not be duplicated
in the MD file and GCC should not perform those transformations by
default.
I am not an expert in this field. I am glad that FMA may be
compliant with IEEE 754. My belief is that basic use of FMA matching the
original expression is different than use of FMA with implicit expression
transformations.
Thanks, David