From owner-freebsd-current@freebsd.org Wed Mar 13 17:16:14 2019 Return-Path: Delivered-To: freebsd-current@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 8631C153A785; Wed, 13 Mar 2019 17:16:14 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Received: from smtp.freebsd.org (smtp.freebsd.org [96.47.72.83]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "smtp.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id E3B7F8AADF; Wed, 13 Mar 2019 17:16:13 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Received: from John-Baldwins-MacBook-Pro-3.local (ralph.baldwin.cx [66.234.199.215]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client did not present a certificate) (Authenticated sender: jhb) by smtp.freebsd.org (Postfix) with ESMTPSA id 5009DA1E8; Wed, 13 Mar 2019 17:16:13 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Subject: Re: Optimization bug with floating-point? To: sgk@troutmask.apl.washington.edu Cc: freebsd-toolchain@freebsd.org, freebsd-current@freebsd.org References: <20190313024506.GA31746@troutmask.apl.washington.edu> <20190313151635.GA34757@troutmask.apl.washington.edu> <20190313164039.GA35340@troutmask.apl.washington.edu> From: John Baldwin Openpgp: preference=signencrypt Autocrypt: addr=jhb@FreeBSD.org; keydata= mQGiBETQ+XcRBADMFybiq69u+fJRy/0wzqTNS8jFfWaBTs5/OfcV7wWezVmf9sgwn8TW0Dk0 c9MBl0pz+H01dA2ZSGZ5fXlmFIsee1WEzqeJzpiwd/pejPgSzXB9ijbLHZ2/E0jhGBcVy5Yo /Tw5+U/+laeYKu2xb0XPvM0zMNls1ah5OnP9a6Ql6wCgupaoMySb7DXm2LHD1Z9jTsHcAQMD /1jzh2BoHriy/Q2s4KzzjVp/mQO5DSm2z14BvbQRcXU48oAosHA1u3Wrov6LfPY+0U1tG47X 1BGfnQH+rNAaH0livoSBQ0IPI/8WfIW7ub4qV6HYwWKVqkDkqwcpmGNDbz3gfaDht6nsie5Z pcuCcul4M9CW7Md6zzyvktjnbz61BADGDCopfZC4of0Z3Ka0u8Wik6UJOuqShBt1WcFS8ya1 oB4rc4tXfSHyMF63aPUBMxHR5DXeH+EO2edoSwViDMqWk1jTnYza51rbGY+pebLQOVOxAY7k do5Ordl3wklBPMVEPWoZ61SdbcjhHVwaC5zfiskcxj5wwXd2E9qYlBqRg7QeSm9obiBCYWxk d2luIDxqaGJARnJlZUJTRC5vcmc+iGAEExECACAFAkTQ+awCGwMGCwkIBwMCBBUCCAMEFgID AQIeAQIXgAAKCRBy3lIGd+N/BI6RAJ9S97fvbME+3hxzE3JUyUZ6vTewDACdE1stFuSfqMvM jomvZdYxIYyTUpC5Ag0ERND5ghAIAPwsO0B7BL+bz8sLlLoQktGxXwXQfS5cInvL17Dsgnr3 1AKa94j9EnXQyPEj7u0d+LmEe6CGEGDh1OcGFTMVrof2ZzkSy4+FkZwMKJpTiqeaShMh+Goj XlwIMDxyADYvBIg3eN5YdFKaPQpfgSqhT+7El7w+wSZZD8pPQuLAnie5iz9C8iKy4/cMSOrH YUK/tO+Nhw8Jjlw94Ik0T80iEhI2t+XBVjwdfjbq3HrJ0ehqdBwukyeJRYKmbn298KOFQVHO EVbHA4rF/37jzaMadK43FgJ0SAhPPF5l4l89z5oPu0b/+5e2inA3b8J3iGZxywjM+Csq1tqz hltEc7Q+E08AAwUIAL+15XH8bPbjNJdVyg2CMl10JNW2wWg2Q6qdljeaRqeR6zFus7EZTwtX sNzs5bP8y51PSUDJbeiy2RNCNKWFMndM22TZnk3GNG45nQd4OwYK0RZVrikalmJY5Q6m7Z16 4yrZgIXFdKj2t8F+x613/SJW1lIr9/bDp4U9tw0V1g3l2dFtD3p3ZrQ3hpoDtoK70ioIAjjH aIXIAcm3FGZFXy503DOA0KaTWwvOVdYCFLm3zWuSOmrX/GsEc7ovasOWwjPn878qVjbUKWwx Q4QkF4OhUV9zPtf9tDSAZ3x7QSwoKbCoRCZ/xbyTUPyQ1VvNy/mYrBcYlzHodsaqUDjHuW+I SQQYEQIACQUCRND5ggIbDAAKCRBy3lIGd+N/BCO8AJ9j1dWVQWxw/YdTbEyrRKOY8YZNwwCf afMAg8QvmOWnHx3wl8WslCaXaE8= Message-ID: Date: Wed, 13 Mar 2019 10:16:12 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:60.0) Gecko/20100101 Thunderbird/60.5.3 MIME-Version: 1.0 In-Reply-To: <20190313164039.GA35340@troutmask.apl.washington.edu> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E3B7F8AADF X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org X-Spamd-Result: default: False [-2.97 / 15.00]; local_wl_from(0.00)[FreeBSD.org]; NEURAL_HAM_SHORT(-0.98)[-0.978,0]; ASN(0.00)[asn:11403, ipnet:96.47.64.0/20, country:US]; NEURAL_HAM_MEDIUM(-1.00)[-0.996,0]; NEURAL_HAM_LONG(-1.00)[-1.000,0] X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 13 Mar 2019 17:16:14 -0000 On 3/13/19 9:40 AM, Steve Kargl wrote: > 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? Oh, I misread your earlier e-mail to say that clang60 worked. One issue I'm aware of is that clang does not have any support for the special arrangement FreeBSD/i386 uses where it uses different precision for registers vs in-memory for some of the floating point types (GCC has a special hack that is only used on FreeBSD for this but isn't used on any other OS's). I wonder if that could be a factor? Volatile probably forces a round trip between memory which might explain why this is the case. I wonder what your test program does on i386 Linux with GCC? -- John Baldwin