Posted by: Anonymous Coward
on June 17, 2005 04:52 AM
Compiling with march=pentium4 does not mean that it uses sse2 and mmx and what not, there are different gcc flags for that. It means the code is optimized for a pentium4 which for 1 is a 32bit CPU so it won't even compile in the 64bit version of whatever functions are being called. Additionally, the pentium4 has a very long pipeline and code optimized for a long pipeline will run slower on a cpu with a short pipeline, say an AMD64.