K6 optimization && compiler builtins

K6 optimization && compiler builtins

[Ronald Wahl]

Hi,

At the moment I'm playing with the string/memory routines of libc which
are written in assembler. On a K6 (somtimes PPro also, Pentium not testet)
I can get a performance gain of 10-40% (!). Now my question: If I use one
of the string/memory functions (e.g. memcmp) in my programs, which one
will be uses - the compiler builtin or the one in the libc? If the builtin
is used - is it possible to include my optimized versions (if ready)?

ron

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Re: K6 optimization && compiler builtins

[Jeffrey A Law]

  In message <Pine.LNX.3.96.971215232539.25052A-100000@goliath.csn.tu-chemnitz.
de>you write:
  > Hi,
  > 
  > At the moment I'm playing with the string/memory routines of libc which
  > are written in assembler. On a K6 (somtimes PPro also, Pentium not testet)
  > I can get a performance gain of 10-40% (!). Now my question: If I use one
  > of the string/memory functions (e.g. memcmp) in my programs, which one
  > will be uses - the compiler builtin or the one in the libc? If the builtin
  > is used - is it possible to include my optimized versions (if ready)?
For the x86, the compiler builtin will be used for memcpy of a constant
number of bytes, I think the compiler builtin will always be used for memcmp.

This can/will differ for other cpus.

jeff

Re: K6 optimization && compiler builtins

[amylaar]

> For the x86, the compiler builtin will be used for memcpy of a constant
> number of bytes, I think the compiler builtin will always be used for memcmp.

Well, always unless waived by -fno-builtin ;-)

Re: K6 optimization && compiler builtins

[Marc Lehmann]

On Mon, Dec 15, 1997 at 11:36:17PM +0100, Ronald Wahl wrote:
> Hi,
> 
> At the moment I'm playing with the string/memory routines of libc which
> are written in assembler. On a K6 (somtimes PPro also, Pentium not testet)
> I can get a performance gain of 10-40% (!). Now my question: If I use one
> of the string/memory functions (e.g. memcmp) in my programs, which one
> will be uses - the compiler builtin or the one in the libc? If the builtin

I guess the compiler builtins will be used (Why not try it out?),
btw, I have a version of strlen that's about 30% faster on
pentiums than the one currently in gcc.

anybody wants to hack it into i386.md?


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Re: K6 optimization && compiler builtins

[Oleg Krivosheev]

hi,

On Mon, 15 Dec 1997, Ronald Wahl wrote:

> Date: Mon, 15 Dec 1997 23:36:17 +0100 (CET)
> From: Ronald Wahl <Ronald.Wahl@informatik.tu-chemnitz.de>
> Reply-To: egcs@cygnus.com
> To: egcs@cygnus.com
> Subject: K6 optimization && compiler builtins
> 
> Hi,
> 
> At the moment I'm playing with the string/memory routines of libc which
> are written in assembler. On a K6 (somtimes PPro also, Pentium not testet)
> I can get a performance gain of 10-40% (!). Now my question: If I use one
> of the string/memory functions (e.g. memcmp) in my programs, which one
> will be uses - the compiler builtin or the one in the libc? 

i believe compiler built-in will be used if known
number of bytes to be copied. I checked once 
what's going on while memcpy double.
Gcc substituted few inlined assembelr instructions
instead of function calls. It was on SPARC though...
Sorry, don't know about x86.

> If the builtin
> is used - is it possible to include my optimized versions (if ready)?

do you have patch against latest snapshot ?

OK

Re: K6 optimization && compiler builtins

[Ronald Wahl]

On Mon, 15 Dec 1997, Oleg Krivosheev wrote:

> > If the builtin
> > is used - is it possible to include my optimized versions (if ready)?
> 
> do you have patch against latest snapshot ?

At the moment no. I'm patching the libc (and linux-kernel) versions
currently. After this I will look at the compiler.

ron

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Re: K6 optimization && compiler builtins

[Stan Cox]

> I have a version of strlen that's about 30% faster on

I would be interested to look at it.
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