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Re: PATCH: Remove SLOW_BYTE_ACCESS from get_best_mode


On Sun, Sep 10, 2006 at 08:37:54PM -0700, Dale Johannesen wrote:
> 
> >I tried this patch on
> >Prescott, Nocona, Core and Core 2. There are no regressions in gcc
> >testsuites nor negative performance impact on SPEC CPU 2K.
> 
> From the documentation, it certainly appears that 1 is the right  
> setting for
> SLOW_BYTE_ACCESS on, at least, all current x86 chips.  The odd thing
> is the Spec regressions you reported on Nocona.  This probably means

With my new patch, I got these on Nocona with gcc 4.2:

			 -O2		-O2 + my patch
164.gzip                 1013            1017    0.394867%
175.vpr                  1109            1103    -0.541028%
176.gcc                  1500            1511    0.733333%
181.mcf                  822             814     -0.973236%
186.crafty               1548            1548    0%
197.parser               960             960     0%
252.eon                  1735            1738    0.172911%
253.perlbmk              1643            1642    -0.0608643%
254.gap                  1683            1680    -0.178253%
255.vortex               1700            1706    0.352941%
256.bzip2                1300            1300    0%
300.twolf                1567            1615    3.06318%
Est. SPECint_base2000    1342            1345    0.223547%

168.wupwise              1842            1839    -0.162866%
171.swim                 2352            2333    -0.807823%
172.mgrid                1157            1163    0.518583%
173.applu                1424            1415    -0.632022%
177.mesa                 1512            1517    0.330688%
178.galgel               2637            2665    1.06181%
179.art                  2165            2406    11.1316%
183.equake               2083            2085    0.0960154%
187.facerec              1448            1452    0.276243%
188.ammp                 1431            1478    3.28442%
189.lucas                2099            2106    0.333492%
191.fma3d                1615            1609    -0.371517%
200.sixtrack             684             684     0%
301.apsi                 1427            1424    -0.210231%
Est. SPECfp_base2000     1623            1639    0.985829%

I didn't see any regressions.

> we should look at the places where SLOW_BYTE_ACCESS is being used;
> if it's being misused[*] that may affect other targets as well as x86.
> You've evaluated the place in stor-layout.c and that's not the problem.
> There are only 2 other places, both in dojump.c.
> 

I don't guite understand how SLOW_BYTE_ACCESS is used in dojump.c. That
is why my new patch doesn't change dojump.c at all and uses a new macro
for stor-layout.c


H.J.


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