Author: Robert Hyatt
Date: 09:01:10 12/23/02
Go up one level in this thread
On December 23, 2002 at 09:45:25, Vincent Diepeveen wrote: >On December 22, 2002 at 08:42:23, Joel wrote: > >>Hey all, >> >>Was reading some of the previous threads where the general consensus seemed to >>be that the Intel C++ 7.0 compiler did a much better job at optimising than the >>VC 6.0 Sp4 compiler did. > >at intel hardware i do not doubt it. > >But it is at your own risk of course whether it is producing correctly >working code for all of your users who also have k7s and perhaps assume >the program must not crash. > >At my K7 the intel compiler crashes time and time again. Also it's slower >than the gcc compiler when using branch profile info (-fbranch-probabilities) >after first generating the info. > >intel without that branch profile info is just like gcc without that info >slower at the k7 than msvc 6 sp4 processor pack. > >the processor pack is crucial for sp4 because it adds a 2% in speed >and the speed differences between default gcc compile and intel c++ compiles >versus msvc sp4 with the procpack is measured at 1% and 0.5% > >but then that profile info increasing the speed for gcc (which is a >time consuming thing, also for the intel compiler of course) is giving >an additional 20% speedup blowing away the other compilers. > >Now let's touch correctness. For a long period of time GCC was a very bad >compiler. Especially many 2.96 versions were very broken. And very buggy. > >Before the 2.95.x versions also there were numerous bugs in gcc with regards >to parallel behaviour (i use 'volatile' variables a lot because diep is >SMP). Also they were dead slow. the 2.95.x versions are dead slow for me >when compared to a default msvc 6 compile. Like 12.5% difference is >no coincidence at a k7. And 10% at a P3. > >But the 3.xx versions are great. If i understand well AMD contributed to >some linux distributions money in order to improve the gcc compiler for >their processors. Of course i have no exact info here i just read around >at the internet for this. > >But the sad thing is that an old 586 compiler msvc6 with a processor pack >that just speeds it up 2% is faster on AMD hardware than the most recent >compilers without that reordering pass. > >Of course this is for DIEP. > >Crafty uses weird 64 bits structures called bitboards it is trivial that >older compilers didn't know how to emulate that very well on 32 bits >processors. It's here only where Bob can claim the intel compiler is >fast for him. I have absolutely no idea what you are talking about. Every gcc compiler after 2.5 worked perfectly with long longs. As does every compiler I have tried in the past 5 years porting crafty to every unix machine made. The intel compiler _is_ faster than gcc 3 for me. And for everyone here at UAB that has tested the two. Too many data points from others, only one from you. I tend to believe the majority. > >for GCC i use next format to compile: > >CFLAGS = -pg -fprofile-arcs -O2 -march=athlon -mcpu=athlon -frename-registers >-DUNIXPII -fno-gcse -foptimize-register-move > >then i run diep for half an hour. > >then i recompile it using: > >CFLAGS = -O2 -march=athlon -fbranch-probabilities -frename-registers >-DUNIXPII -fomit-frame-pointer -fno-gcse -foptimize-register-move > >in case of boundschecking: > >#CFLAGS = -g -DUNIXPII -O2 -fbounds-checking -Wall > ># intel c++ nu >#CC = icc >#CPP = icc >#CFLAGS = -g -DUNIXPII >#CFLAGS = -O3 -tpp6 -axi -xi -rcd -prof_genx -DUNIXPII >#CFLAGS = -O3 -tpp6 -axi -xi -rcd -prof_use -DUNIXPII > >Best regards, >Vincent > >>My compiler knowledge is very limited - I have written a C compiler before (uni >>assignment), but optimisation wasn't an issue. I have no real idea how an >>optimising compiler goes about it's work. >> >>For the record I have an Athlon XP 2100+, and my engine is bitboard based. >> >>Having said that, I installed the Intel compiler, and tried compiling my latest >>version of Bodo, and then ran my dodgy little speed benchmark on it. It was >>actually slower than the VC 6.0 compiler, though I have reason to suspect my >>incompetence is the issue, largely due to statements like: >> >>"Did you use the intel C++ 7.0? Of course not. Did you do the profile-feedback >>optimizations? Probably not." > >>What I am asking is how do I do this profile-feedback optimisations, and or any >>other optimisations which you guys do? > >>What would be particularly helpful is other people could give me the compiler >>command line parameters they use to generate fast code. > >>I really need to buy a book on optimising compilers so I understand what the >>hell is happening here. :| > >>Any help greatly appreciated, >>Joel Veness
This page took 0.01 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.