Date: Wed, 10 Oct 2007 09:46:16 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: d@delphij.net Cc: freebsd-arch@freebsd.org Subject: Re: Why we optimize by time by default for < -O2 case? Message-ID: <20071010092255.O36751@delplex.bde.org> In-Reply-To: <470AED31.60201@delphij.net> References: <470ACEA1.3030309@delphij.net> <20071009122751.X54949@besplex.bde.org> <470AED31.60201@delphij.net>
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On Mon, 8 Oct 2007, LI Xin wrote: > Bruce Evans wrote: >>> Revision Changes Path >>> 1.15 +0 -0 src/contrib/gcc/toplev.c >> >> Without this change, -O pessimizes for time. > > Does this affect all platforms or is it i386 only, on the latest GCC > version? I don't know, but guess it affects some. In general, the pessimization works by breaking lookup of a table that gives the best alignment for the current target, so it affects all platforms that have such a table. On platforms with stricter alignment requirements than i386, gcc would have to adjust any -falign-foo settings that are too small to work. Then the pessimization might give minimal aligment != 1 and thus have no effect if the minimal alignment happens to equal the best alignment. Bruce
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