http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54239
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-08-13 13:58:40 UTC --- But the Intel manual AFAIK doesn't talk about prefetch insn. So, the -mprfchw switch needs to control solely the prefetchw instruction, and there might be a different one that controls the prefetch insn. In driver-i386.c you could enable -mprfchw vs. ?-mprfch -mpfrchw? based on whether the CPU is Intel or AMD or something, but if there are CPUs that don't have both insns, it needs to be enabled independently. Areg?
