From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dan McGee <dpmcgee@gmail.com>
Subject: Re: [PATCH 4/5] tree-walk: unroll get_mode since loop boundaries are well-known
Date: Wed, 6 Apr 2011 15:45:59 -0500
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Cc: Junio C Hamano <gitster@pobox.com>, git@vger.kernel.org,
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To: Antriksh Pany <antriksh.pany@gmail.com>
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On Tue, Apr 5, 2011 at 6:55 PM, Antriksh Pany <antriksh.pany@gmail.com> wrote:
> On Mon, Apr 4, 2011 at 10:33 PM, Dan McGee <dpmcgee@gmail.com> wrote:
>> ....
>> Totally agree; I should have tried to do it this way in the first
>> place. However, compiling the fixed-length 0 to 5 loop does not
>> produce fully-unrolled assembly for me with CFLAGS="-march=native
>> -mtune=native -O2 -pipe -g" on x86_64. I see two copies of the loop
>> only, and even worse is the (lack of) performance (each is the mode of
>> 3 runs). Compilers are stupid apparently.
>> ....
>
> Can you try -O3? Or an explicit '-funroll-loops'?
> gcc I think does not do aggressive speed optimizations at the cost of
> space when at O2.

Sure- both of these options show the loop being unrolled for all 5
iterations. However, that doesn't help me and the other 95% of people
using distro packages, git-scm.com binaries, or anyone compiling with
the default CFLAGS optimization level which is unfortunate.

-Dan