Author: Vincent Diepeveen
Date: 09:12:29 12/23/02
Go up one level in this thread
On December 23, 2002 at 12:01:10, Robert Hyatt wrote: You forget the crucial data point and that's that you have no AMD K7s out there. >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
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