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Re: Performance of Integer Multiplication on PIII
- To: Kevin Atkinson <kevin at atkinson dot dhs dot org>
- Subject: Re: Performance of Integer Multiplication on PIII
- From: Jan Hubicka <jh at suse dot cz>
- Date: Sat, 3 Nov 2001 17:44:33 +0100
- Cc: gcc at gcc dot gnu dot org
- References: <Pine.LNX.4.33L2.0111021319050.16076-100000@kevin.inet>
> When running these same tests on on Mobile Pentium MMX (using -march=i586)
> Gcc code does out perform mine. I do not have anything in between to run
> these tests on so I would appreciate it if someone with a Pentium Pro and
> PII (or is that the same thing as a Pentium Pro?) could run them and post
> the results.
>
> So I guess the lesson here is that on PIII integer multiplication is fast
DId the timming in PIII of imul instruction changed?
Gcc believes its latency to be 4 cycles for PPro to PIII. THe core is same,
but there may be small differences. Is this the case?
Honza
> enough that doing special tricks to avoid integer multiplication will hurt
> performs in stead of helping it.
>
> Is this a known issue? And if so does anyone plan on addressing it. I
> seams to me that the only fix would me to introduce more options for
> -march and -mcpu for the faster Pentiums.
>
> Thanks in advance.