Date: Sat, 10 Oct 2015 15:14:40 +0000 From: Ed Maste <emaste@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, Dimitry Andric <dim@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r289072 - in head/contrib: libc++/src llvm/lib/Transforms/Vectorize Message-ID: <CAPyFy2Au-Wge3oHNOuecHDRWEaHyrFbus2BDvwLpPFDUOskVAg@mail.gmail.com> In-Reply-To: <20151010125348.GF2257@kib.kiev.ua> References: <201510091821.t99ILjHI054211@repo.freebsd.org> <20151010060846.GA2257@kib.kiev.ua> <CAPyFy2Dm=OaJbTfwVDABPz=e_H-XhhnTc%2BjYtr0iSHYv3uEObw@mail.gmail.com> <20151010120311.GE2257@kib.kiev.ua> <CAPyFy2BsS3Z7izEtWGqyXJkBcoykOX5y144w4Q997TKwWxaYDQ@mail.gmail.com> <20151010125348.GF2257@kib.kiev.ua>
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On Oct 10, 2015 8:53 AM, "Konstantin Belousov" <kostikbel@gmail.com> wrote: > > On Sat, Oct 10, 2015 at 12:24:33PM +0000, Ed Maste wrote: > > On 10 October 2015 at 12:03, Konstantin Belousov <kostikbel@gmail.com> wrote: > > >> The declaration is extern ostream cout; which correctly has 8 byte alignment. > > > The alignment of the declaration does not matter, most likely. > > > I am not sure what you mean by saying that 8 byte alignment is desirable, > > > while compiler generates accesses (movdqa) which assume 16-byte alignment. > > > > I mean that this object is naturally expected to have 8-byte > > alignment. In previous versions of libc++.so shipped with FreeBSD it > > did, and can't be changed now (cout comes from the binary itself, via > > a copy relocation). > No, the natural alignment for char[] is 1, while ABI requires an array > longer than 15 bytes to have 16-bytes alignment. Right, but the proper alignment for ostream is 8; it's only because of the slightly bizarre definition as a char array that we end up with this 16 byte ABI alignment.
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