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Re: IEEE 754 and fused-madd (was: Re: patch: rs6000 specific)
- From: Dale Johannesen <dalej at apple dot com>
- To: David Edelsohn <dje at watson dot ibm dot com>
- Cc: Dale Johannesen <dalej at apple dot com>, Stan Shebs <shebs at apple dot com>, lucier at math dot purdue dot edu, gcc-patches at gcc dot gnu dot org
- Date: Fri, 7 Dec 2001 12:39:05 -0800
- Subject: Re: IEEE 754 and fused-madd (was: Re: patch: rs6000 specific)
All right, so I need to generate additional FMA patterns by modifying
combine.
Our FP expert says all the required transformations are IEEE-compliant.
Before I get too far into it, does anybody want to dispute this? Here are
the patterns. The claim is that each of them can be transformed safely
into the first one in its group.
fmadd:
A*C + B
B + A*C
fnmsub:
-(A*C - B)
((-A)*C) + B
-((-B) + A*C)
B - A*C
fmsub:
A*C -B
-B + A*C
-(B - A*C)
-((-A)*C + B)
fnmadd:
-(A*C + B)
((-A)*C) -B
(-B) - A*C
-(B + A*C)