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[Bug tree-optimization/32183] [4.3 Regression] reassoc2 can more extra calculations into a loop
- From: "hjl at lucon dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 2 Jun 2007 14:20:24 -0000
- Subject: [Bug tree-optimization/32183] [4.3 Regression] reassoc2 can more extra calculations into a loop
- References: <bug-32183-682@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #16 from hjl at lucon dot org 2007-06-02 14:20 -------
Here are SPEC CPU 2K -O2 -ffast-math differences between revision
125029 and revision 125029 on Intel64 C2D:
(r125030 - r125029)/r125029
164.gzip 0.0706714%
175.vpr -0.116077%
176.gcc -1.83805%
181.mcf 0.968263%
186.crafty 0.351975%
197.parser -0.15456%
252.eon -0.324675%
253.perlbmk -0.0394945%
254.gap -0.318471%
255.vortex 0.211775%
256.bzip2 0.300601%
300.twolf 0%
Est. SPECint_base2000 -0.0983284%
168.wupwise 0.92511%
171.swim -0.0767165%
172.mgrid 0.179856%
173.applu -3.62731%
177.mesa 0.0398565%
178.galgel -4.55329%
179.art -1.38686%
183.equake 0.303819%
187.facerec -0.383583%
188.ammp -0.7768%
189.lucas -1.30465%
191.fma3d 1.38667%
200.sixtrack -0.135318%
301.apsi 0.0545256%
Est. SPECfp_base2000 -0.660502%
Here are SPEC CPU 2K -O2 -ffast-math differences between revision
125029 with DCE change disabled and revision 125029 on Intel64:
(r125030 no DCE - r125029)/r125029
164.gzip 0.0706714%
175.vpr 0%
176.gcc 0%
181.mcf 0.484131%
186.crafty 0.195542%
197.parser -0.15456%
252.eon -0.202922%
253.perlbmk 0.35545%
254.gap 0.181984%
255.vortex 0.16942%
256.bzip2 -0.150301%
300.twolf 0.0389257%
Est. SPECint_base2000 0.0983284%
168.wupwise 0.264317%
171.swim -0.0383583%
172.mgrid 0%
173.applu 0.0711238%
177.mesa 0%
178.galgel 0.123062%
179.art -3.16302%
183.equake 0.0434028%
187.facerec -0.115075%
188.ammp 0.0517866%
189.lucas 0.0705219%
191.fma3d 0%
200.sixtrack -0.135318%
301.apsi 0.163577%
Est. SPECfp_base2000 -0.176134%
Given the impact of DCE change, it isn't a real surprise. It not only may not
optimize loop, but may make a loop to run slow. I will bet you will find the
similar results on other architectures.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32183