Date: Thu, 24 Oct 2019 15:34:33 +0000 From: Alexey Dokuchaev <danfe@freebsd.org> To: Warner Losh <imp@bsdimp.com> Cc: Dimitry Andric <dim@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all <svn-src-all@freebsd.org>, svn-src-head <svn-src-head@freebsd.org> Subject: Re: svn commit: r353936 - head/contrib/llvm/tools/clang/lib/Driver/ToolChains/Arch Message-ID: <20191024153433.GA68256@FreeBSD.org> In-Reply-To: <CANCZdfrqdy9MBX6JfrY%2BkBCQY=xZABAnS=VF7U4KWZzVo9Qj6w@mail.gmail.com> References: <201910231657.x9NGvCMD039111@repo.freebsd.org> <20191024082609.GA63459@FreeBSD.org> <CANCZdfrqdy9MBX6JfrY%2BkBCQY=xZABAnS=VF7U4KWZzVo9Qj6w@mail.gmail.com>
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On Thu, Oct 24, 2019 at 09:14:07AM -0600, Warner Losh wrote: > On Thu, Oct 24, 2019 at 2:26 AM Alexey Dokuchaev <danfe@freebsd.org> wrote: > > On Wed, Oct 23, 2019 at 04:57:12PM +0000, Dimitry Andric wrote: > > > New Revision: 353936 > > > URL: https://svnweb.freebsd.org/changeset/base/353936 > > > > > > Log: > > > Bump clang's default target CPU for the i386 architecture (aka > > > "x86") to i686, as per the discussion on the freebsd-arch mailing > > > list. > > > > Why i686, not i586? i486 lacking 64-bit atomics is a sound and valid > > reason, but I don't understand why i586 wasn't chosen, and quick review > > of that -arch thread did not help. > > There were several notions at play here. First, the rest of the i386 > ecosystem has defaulted to i686 for a long time. [...] > > i686 support by default allows better code generation and increased > performance. The biggest thing being using CMOVxx instructions to avoid > a pipeline miss due to branching, though there's likely others. > > By moving to i686 by default, we have only one bump instead of two. [...] > > So that's where we are: a mix of technical and political reasons were why > we bumped up to i686 by default Understood. I appreciate long and elaborate reply Warner. > Chances are this will be the last minimum bump as well before i386 is > removed from the tree as irrelevant (some years from now, but the day > will come). I hope the day never comes, as I don't want to be forced from FreeBSD to something else on vast majority of my hardware. ./danfe
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