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Re: [PATCH] Reduce the number of extraneous rtl when expanding mutliply

From: Andrew Pinski <pinskia at physics dot uc dot edu>
To: Roger Sayle <roger at eyesopen dot com>
Cc: <gcc-patches at gcc dot gnu dot org>, Steven Bosscher <stevenb at suse dot de>
Date: Fri, 12 Nov 2004 10:37:08 -0500
Subject: Re: [PATCH] Reduce the number of extraneous rtl when expanding mutliply
References: <Pine.LNX.4.44.0411091954500.893-100000@www.eyesopen.com>

On Nov 9, 2004, at 10:41 PM, Roger Sayle wrote:

On Tue, 9 Nov 2004, Andrew Pinski wrote:

	* expmed.c (expand_mult_const): If we have an alg_m as the first
	operation and there is only one other operation, then don't copy
	the register into a new one.


I don't think this is safe.  I was just about to approve this patch
(under the condition that you mention PR middle-end/18293 in the
ChangeLog) when I it struck me that we can't use op0 directly as
the accumulator, as op0's pseudo mustn't be modified, but the
accum pseudo may potentially be modified in place.

It does not matter if it is not safe or not anymore, we can produce
worse code with this patch as the IV-OPT cost analysis is being messed
up by not having the extra copy in there.

I am going to put this on back burner for now.

Thanks,
Andrew Pinski

Follow-Ups:
- Re: [PATCH] Reduce the number of extraneous rtl when expandingmutliply
  - From: Roger Sayle

References:
- Re: [PATCH] Reduce the number of extraneous rtl when expandingmutliply
  - From: Roger Sayle

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