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List Archive: gentoo-performance
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To: gentoo-performance@g.o
From: Andrea Pretto <prettz_it@...>
Subject: Re: gcc optimizations
Date: Thu, 1 Jul 2004 11:17:49 +0200 (CEST)
Gcc cannot to preview the contents of  "if{ ... }".
In this case there is a single instruction, but in
others cases the if  statement can contain a lot of
instructions.
The I think gcc deals the "if" mechanically, and it
don't look for particular "if" with one istruction as
in your example.

After that, there is not a flag or a special
opitmization that favourite use of cmov in asm code,
cmov it's only a instruction.Than you can use it
"manually" in inline assembler.

--- Paul Ingelbrant <pi@...> ha scritto: >
Quoting Andrea Pretto <prettz_it@...>:
> 
> > The flag -mmmx ( like -msse -m3dnow etc...)
> activate
> > some extensions for C language.
> > 
> > See this:
> >
>
http://gcc.gnu.org/onlinedocs/gcc-3.3.3/gcc/X86-Built-in-Functions.html#X86%20Built-in%20Functions
> > 
> > So, those flag activate these built-in functions.
> 
> I see. 
> 
> But what's the matter with the cmov instruction?
> Should be reasonably "simple"
> for  gcc to use it automatically...  
> 
> --
> gentoo-performance@g.o mailing list
> 


	

	
		
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References:
Re: gcc optimizations
-- Paul Ingelbrant
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Updated Jun 17, 2009

Summary: Archive of the gentoo-performance mailing list.

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