On Mon, Nov 28, 2011 at 1:56 PM, Florian Philipp <li...@binarywings.net> wrote: > Am 28.11.2011 18:56, schrieb Michael Mol: >> On Mon, Nov 28, 2011 at 11:46 AM, Pandu Poluan <pa...@poluan.info> wrote: >> No, you've got some ugly flags in there. -fexcess-precision and >> -funsafe-math-optimizations, in particular. (I must have been talking >> to someone else last week; sorry, I'm terrible with names.) >> > > I doubt -fexcess-precision=fast does anything at all. Pandu uses an > AMD64 system, right? Then you have -mfpmath=sse set per default and SSE > does not have excess precision issues (that's just for the old x87 FPU). > Even if you used that, is redundant because of your other flags. To > quote `man gcc`: > "-fexcess-precision=standard is not implemented for languages other than > C, and has no effect if -funsafe-math-optimizations or -ffast-math is > specified." <-- Therefore you always have ..=fast anyway. > > -funsafe-math-optimizations is really terrible. Either you us floating > point arithmetic, then you have to rely on it because it is hard enough > already to gain necessary precision with it, or you don't, then you > don't need that flag because it doesn't improve performance.
I didn't know (or forgot) what arch he was using. >> -fomit-frame-pointer shouldn't cause any headaches unless you're >> feeding a gdb stack trace, and you're not adding any debugging data, >> so your stack traces would be pretty useless, anyway. >> > > If you are on an AMD64 system, this flag is implied because it doesn't > affect stack traces on x86_64 anymore. AMD64 puts the requisite data in its own register, right? Yeah, it sounds like Pandu's setup CFLAGS can use some cleanup. >> I don't know about -floop-interchange, -floop-strip-mine or >> -floop-block. I recognize at least one of them from the discussion of >> graphite the other day. >> > > These definitely need graphite to have any effect. Then they should be > reasonably safe (as far as anything relying on experimental compiler > frameworks can be considered safe). Upstream devs might take issue with them, but I'm still not sure they should affect bug reports of build-time failures. I would *hope* upstream gcc is doing tests on its own build tools compiled with its graphite optimizations. I don't know about make and autotools, though. -- :wq
