Barry, thank you for your reply. I only thought that there was a problem with gcc and higher optimizations. I have for example a problem with gcc 4.6 as when I compile my program with -O3 the result would then not converge any more. With the optimisation -O2 it works all well also all other gcc I had before made no problems. So I thought as configure set gcc with only -O and icc with -O3 there was generally a problem with gcc and optimizations. But if not it is good.
Manfred Barry Smith schrieb: > Manfred, > > ./configure is not smart enough to know what optimization flags are best > for all compilers/systems. Thus we have relatively straightforward defaults. > As Jed notes, if you know what flags are most appropriate for your build you > must pass them in to ./configure > > Barry > > On May 8, 2012, at 7:59 AM, Jed Brown wrote: > > >> On Tue, May 8, 2012 at 1:32 AM, Manfred Gratt <manfred.gratt at uibk.ac.at> >> wrote: >> when I compile petsc with --with-debugging=0 with gcc and icc in configure >> there are different optimization flags set depending on compiler. So is with >> gcc -O set wich means -O1 optimization. While with icc -O3 optimisation is >> set. Is there a reason only icc gets the high performance flag while gcc >> not? Are there any problems when some optimizations are activated on gcc? >> >> I don't know why only -O1 is used with gcc, but you can pass COPTFLAGS='-O3 >> -march=native' or whatever you like to configure to make it use those >> instead. >> > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120509/833f1ab2/attachment.htm>
