linux-kernel - Re: [PATCH 0/1] vsprintf: optimize decimal conversion (again)

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Message-ID: <CAK1hOcO7YpLUebe=+TmN2WLyuFPqAyLNco1B7q+mhE2_BmAe3A@mail.gmail.com>
Date:	Thu, 29 Mar 2012 12:35:22 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	roma1390 <roma1390@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Douglas W Jones <jones@...uiowa.edu>,
	Michal Nazarewicz <mnazarewicz@...gle.com>
Subject: Re: [PATCH 0/1] vsprintf: optimize decimal conversion (again)

On Wed, Mar 28, 2012 at 12:33 PM, Denys Vlasenko
<vda.linux@...glemail.com> wrote:
> On Wednesday 28 March 2012 12:24, roma1390 wrote:
>> On 2012.03.28 13:13, Denys Vlasenko wrote:
>> > Second: run
>> > arm-linux-gnueabi-gcc -O2 -Wall test_{org,new}.c -S
>> > and email me resulting test_{org,new}.s files.
>>
>> test_{org,new}.s attached.
>
> Bingo.
>
>        bl      __aeabi_uidivmod
>
> Not good. Your gcc did not optimize division by constant.
>
> Can you add  "noinline_for_stack":
>
> static noinline_for_stack <=== HERE
> char *put_dec(char *buf, unsigned long long n)
>
> and regenerate and resend the test_new.s?

Since you confirmed that noinlining helps,
I recommend you to file a gcc bug report:
your gcc misses an optimization when it inlines
that function.

-- 
vda
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