Jeff Law <l...@redhat.com> writes: > On 03/14/2012 10:30 AM, Joseph S. Myers wrote: >> >> I'd say that "better performance with the potential loss of accuracy" >> should be covered by -ffast-math - that GCC should generate direct use of >> fsin/fcos instructions for sin/cos for -O2 -funsafe-math-optimizations on >> x86_64, as it does on x86, unless there is some reason to think they would >> perform worse than the out-of-line implementation. > The better performance with potential loss of accuracy is an across > the board request, it's not just a sin/cos issue. All the trig, exp, > pow, log, etc, which I don't think are necessarily covered by using > the old x87 fp unit.
Note that various interesting CPUs (like Atom) have a very slow x87 units and it's generally deprecated and discouraged. So if you go for a new libm it's better to be SSE only (ideally AVX too) and avoid any usage of x87. One big win alone on 32bit x86 would be to use a SSE ABI for libm by default. You may still need some fallback for old CPUs, but this doesn't need to be terrible optimized. -Andi -- a...@linux.intel.com -- Speaking for myself only
