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Re: GCC 4.1.0 Released


On Wed, Mar 01, 2006 at 02:19:47PM -0800, Mark Mitchell wrote:
> H. J. Lu wrote:
> 
> > Here are diffs of SPEC CPU 2K between before and after with gcc 4.1
> > using "-O2 -ffast-math" on Nocona:
> 
> Steven's right; this is clearly a new feature.  HJ's also right; we've
> made exceptions before.
> 
> Like Steven, I would like to see what the difference is between
> -mtune=generic and -mtune=nocona.  If there is not much difference, then

Here are diffs of "-O2 -mtune=nocona -ffast-math" vs
"-O2 -mtune=generic -ffast-math" on Nocona:

164.gzip	1.30%
175.vpr	-0.29%
176.gcc	-4.04%
181.mcf	0.74%
186.crafty	1.65%
197.parser	-0.10%
252.eon	-0.38%
253.perlbmk	5.25%
254.gap	0.93%
255.vortex	1.54%
256.bzip2	0.72%
300.twolf	9.70%
SPECint_base2000	1.31%
	
168.wupwise	2.49%
171.swim	-0.55%
172.mgrid	6.46%
173.applu	0.65%
177.mesa	2.56%
178.galgel	0.14%
179.art	1.79%
183.equake	0.79%
187.facerec	-0.07%
188.ammp	4.86%
189.lucas	1.21%
191.fma3d	1.08%
200.sixtrack	0.00%
301.apsi	1.21%
SPECfp_base2000	1.62%

I'd like to see the default -O2 generate decent code for Nocona. It
is independent of improviong -mtune=nocona for Nocona.

> that's an argument against a backport; just tell users to add
> -mtune=nocona.  It's up to architecture maintainers to get defaults set
> well for their systems in advance of releases.
> 
> I'd also like to hear from our IA32 maintainers.

My IA32 numbers show that -mtune=generic gives the better SPEC CPU 2K
-O2 numbers on Dothan, Yonah, Northwood and Yonah than the previous
-O2 option.

> 
> 2. IA32 is one of, if not the, most popular GCC architectures.  On the
> one hand, yes, that argues for making it perform well there; on the
> other, it also argues very strongly for stability.  Effectively changing
> the default optimization behavior on a release branch substantially
> invalidates previous validation done on that branch.
> 

The last thing I want to see is the instability on IA32. I can't
guarantee it won't happen. But I will do my best to fix it if the
backported patch is the cause.


H.J.


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