http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54239
--- Comment #2 from Venkataramanan <venkataramanan.kumar at amd dot com> 2012-08-13 13:51:08 UTC --- (In reply to comment #1) > Both in 4.7 (which is before the prfchw changes) and 4.8 with -m32 -m3dnow and > -m32 -m3dnow -mno-sse I get prefetch + prefetchw insn, which looks ok to me. > -mno-mmx I think disables 3dnow too, so you get no prefetch insns in that case > (which is also fine). -mprfchw implies the SSE prefetches and PRFCHW CPUID > 0x80000001 ecx bit 8 doesn't imply the prefetch insn, just prefetchw, so it is > correct that with -m32 -mprfchw prefetchnta + prefetchw is generated. > So, where exactly do you see a bug? Hi Jakub, > -mprfchw implies the SSE prefetches and PRFCHW CPUID > 0x80000001 ecx bit 8 doesn't imply the prefetch insn, just prefetchw, so it is > correct that with -m32 -mprfchw prefetchnta + prefetchw is generated. > So, where exactly do you see a bug As per AMD cpuid manual, 0x80000001 ecx bit 8 impiles both prefetch and prefetchw. http://blogs.amd.com/developer/2010/08/18/3dnow-deprecated/
