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Re: [PATCH] Use strlen when searching for a nul char
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: libc-alpha at sourceware dot org
- Date: Tue, 19 Apr 2016 17:27:16 -0300
- Subject: Re: [PATCH] Use strlen when searching for a nul char
- Authentication-results: sourceware.org; auth=none
- References: <DB3PR08MB008978DA72CE0E1B93BB477483A60 at DB3PR08MB0089 dot eurprd08 dot prod dot outlook dot com> <20160419175706 dot GI5369 at vapier dot lan>
On 19-04-2016 14:57, Mike Frysinger wrote:
> On 25 Feb 2016 13:04, Wilco Dijkstra wrote:
>> Remove the strchr (s, '\0') to rawmemchr optimization as using rawmemchr is
>> a bad idea - I have a patch to add strchr (s, '\0') -> strlen to GCC7.
>> Like strchr (s, '\0'), rawmemchr (s, '\0') appears a common idiom for finding
>> the end of a string, however it is not the most efficient way of doing so.
>> Strlen is a simpler operation which is significantly faster on larger inputs
>> (eg. on x86 strlen is 50% faster than rawmemchr on strings of 1KB).
> will there be a change in GCC to also detect rawmemchr(s,'\0') ?
> even then, since this optimization isn't showing up until GCC7, shouldn't
> we keep some logic here ? i.e. transform strchr/rawmemchr(s, '\0') into
> strlen before falling back ?
Personally I am not very found on the string2.h header and its intrinsic logic,
which contains optimization logic that might not be true depending of the
architecture string optimization.
Also for the specific optimization does we really need to keep pushing for
these specific inline implementations? I would prefer a much simple string2.h
header than a convoluted one we have today.