Date: Wed, 13 Mar 2019 09:40:39 -0700 From: Steve Kargl <sgk@troutmask.apl.washington.edu> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-toolchain@freebsd.org, freebsd-current@freebsd.org Subject: Re: Optimization bug with floating-point? Message-ID: <20190313164039.GA35340@troutmask.apl.washington.edu> In-Reply-To: <e290b68f-7a1d-2456-4a0c-9f7dfd303f55@FreeBSD.org> References: <20190313024506.GA31746@troutmask.apl.washington.edu> <20190313151635.GA34757@troutmask.apl.washington.edu> <e290b68f-7a1d-2456-4a0c-9f7dfd303f55@FreeBSD.org>
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On Wed, Mar 13, 2019 at 09:32:57AM -0700, John Baldwin wrote: > On 3/13/19 8:16 AM, Steve Kargl wrote: > > On Tue, Mar 12, 2019 at 07:45:41PM -0700, Steve Kargl wrote: > >> > >> gcc8 --version > >> gcc8 (FreeBSD Ports Collection) 8.3.0 > >> > >> gcc8 -fno-builtin -o z a.c -lm && ./z > >> gcc8 -O -fno-builtin -o z a.c -lm && ./z > >> gcc8 -O2 -fno-builtin -o z a.c -lm && ./z > >> gcc8 -O3 -fno-builtin -o z a.c -lm && ./z > >> > >> Max ULP: 2.297073 > >> Count: 0 (# of ULP that exceed 21) > >> > > > > clang agrees with gcc8 if one changes ... > > > >> int > >> main(void) > >> { > >> double re, im, u, ur, ui; > >> float complex f; > >> float x, y; > > > > this line to "volatile float x, y". > > So it seems to be a regression in clang 7 vs clang 6? > /usr/local/bin/clang60 has the same problem. % /usr/local/bin/clang60 -o z -O2 a.c -lm && ./z Maximum ULP: 23.061242 # of ULP > 21: 39 Adding volatile as in the above "fixes" the problem. AFAICT, this a i386/387 code generation problem. Perhaps, an alignment issue? -- Steve 20170425 https://www.youtube.com/watch?v=VWUpyCsUKR4 20161221 https://www.youtube.com/watch?v=IbCHE-hONow
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