Date: Thu, 06 Sep 2012 14:57:21 +0200 From: Dimitry Andric <dimitry@andric.com> To: David Chisnall <theraven@FreeBSD.org> Cc: Garrett Cooper <yanegomi@gmail.com>, Roman Divacky <rdivacky@FreeBSD.org>, freebsd-current@FreeBSD.org, Steve Kargl <sgk@troutmask.apl.washington.edu> Subject: Re: Compiler performance tests on FreeBSD 10.0-CURRENT Message-ID: <50489DB1.4070102@andric.com> In-Reply-To: <122361C5-7B83-494B-A580-970FAFF83CAA@FreeBSD.org> References: <5046670C.6050500@andric.com> <20120904214344.GA17723@troutmask.apl.washington.edu> <504679CB.90204@andric.com> <20120904221413.GA19395@troutmask.apl.washington.edu> <CAGH67wTQavfh9ExsjypnCjw4yrV2RpdUUjxAD2kaZy-PiDocHA@mail.gmail.com> <50471BEE.6030708@andric.com> <20120905221310.GA97847@troutmask.apl.washington.edu> <20120906084312.GA13223@freebsd.org> <122361C5-7B83-494B-A580-970FAFF83CAA@FreeBSD.org>
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On 2012-09-06 12:20, David Chisnall wrote: ... > There may also be a difference in whether -ffast-math is the default on each compiler. On x86, this will replace a number of libm calls with (much faster, but less accurate) SSE or x87 instructions. If this is enabled by default with clang and not with gcc, it would account for the difference. No, -ffast-math is not enabled by default in clang, as far as I can tell. Also, the help text for the option says: "Enable the *frontend*'s 'fast-math' mode. This has no effect on optimizations, but provides a preprocessor macro __FAST_MATH__ the same as GCC's -ffast-math flag."
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