Author: Frank Phillips
Date: 15:43:20 02/16/05
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On February 16, 2005 at 17:46:23, Vincent Diepeveen wrote: >On February 16, 2005 at 13:09:14, Frank Phillips wrote: > >>Has anybody got any experience with g++ 3.4 for amd64 (x86_64) - for Linux? >> >>I have been using the profile generated optimisation option, but the code it >>produces is no faster then with simple -O3. >> >>I simply compile with -fprofile-generate >>then run, >>then recompile with -fprofile-use. >> >>The relevant *.gcno, *.gcda files are produced. Must be doing something >>wrong..... >> >>Frank > >First of all get the LATEST version of gcc. thats 3.4.3 now. and if when i post >3.4.4 is released get that one. like bob my experience is that the PGO in gcc is >pretty buggy. > >icc is however such a bad optimizing compiler that gcc is far faster for diep. i >guess icc is better bugfixed for 64 bits code as that mattered for specint2000, >guess why :) > >Anyway gcc isn't that great in 64 bits perhaps, but it's scheduling better for >opteron than icc is, which for diep is more important. icc of course is only >good for intel hardware when your program hasn't been in specint yet. > >main idea is. delete all your files except source files. > >THEN run the fprofile generate single cpu. > >then delete all object files > >then run the profile use. > >never use intel c++. they will do anything to slow you down at AMD hardware. > >Vincent Thanks, I do remove object files before recompiling after the profile run. What is confusing, is that I get no speed up at all over plain -O3, which made me suspect I must be doing something wrong. (Although all I have done is change fprofile-arcs / fprofile-branch-probabilites to fprofile-generate / fprofile-use in the makefile and the latter pair did have an effect in gcc3.3 - I think.). Frank BTW icc gave me 20-30% speed up in 32 bit mode over gcc. My program is an unholy mixture of bitboards and array look-up for move generation. The 64 bit amd and slower gcc slightly overcompensates for the loss of the 32bit Intel compiler.
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