Date: Fri, 14 Aug 2015 09:37:43 +0800 From: Erich Dollansky <erichsfreebsdlist@alogt.com> To: Davide Italiano <davide.italiano@gmail.com> Cc: Andriy Gapon <avg@freebsd.org>, Konstantin Belousov <kostikbel@gmail.com>, "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: allow ffs & co. a binary search Message-ID: <20150814093743.267af1c5@X220.alogt.com> In-Reply-To: <CACYV=-FU=obZpzg4T_M_3k43yi5oieiKnOrPJEdZNEuKdMRdEQ@mail.gmail.com> References: <20150607081315.7c0f09fb@B85M-HD3-0.alogt.com> <5573EA5E.40806@selasky.org> <20150607195245.62dc191f@B85M-HD3-0.alogt.com> <20150607135453.GH2499@kib.kiev.ua> <558175FA.4040106@FreeBSD.org> <20150617165331.GA2080@kib.kiev.ua> <5582CCF1.8010505@FreeBSD.org> <CACYV=-FU=obZpzg4T_M_3k43yi5oieiKnOrPJEdZNEuKdMRdEQ@mail.gmail.com>
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Hi, On Thu, 13 Aug 2015 16:37:08 -0400 Davide Italiano <davide.italiano@gmail.com> wrote: > On Thu, Jun 18, 2015 at 9:51 AM, Andriy Gapon <avg@freebsd.org> wrote: > > On 17/06/2015 19:53, Konstantin Belousov wrote: > >> AFAIR it was about 'sufficiently smart compiler' and the fact that > >> the functions are not on the hottest paths. > > > > It seems that sufficiently smart compilers still do not exist :-) > > At least as far as compilers that are used for compiling FreeBSD > > are considered. > > > > [Offtopic] my impression is that lately smartness of compilers is > > mostly being improved by various tricks and shortcuts (undefined > > behavior, etc), rather than by recognizing patterns in the C code > > that could be turned into more efficient machine code. > > > > -- > > Andriy Gapon > > _______________________________________________ > > freebsd-hackers@freebsd.org mailing list > > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > > To unsubscribe, send any mail to > > "freebsd-hackers-unsubscribe@freebsd.org" > > Sorry for resurrect an old thread. > I fixed in LLVM upstream (I'll try to get this pulled in FreeBSD). > http://llvm.org/viewvc/llvm-project?view=revision&revision=244947 > It seems that we can still save another instruction, but LLVM is close > enough to gcc now in code generation for this pattern. > what does this mean? Does clang now recognise loops like this or is the built-in function now optimised? Erich
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