Re: gcc optimizations
Andrea Pretto <[email protected]>
| Newsgroups | gmane.linux.gentoo.performance |
|---|---|
| Message-ID | <[email protected]> |
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 <[email protected]> ha scritto: >
Quoting Andrea Pretto <[email protected]>:
>
> > 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...
>
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>
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