Re: unroll-loops - Is it always safe?

2007-04-05 Thread Gary Kline 
On Thu, Apr 05, 2007 at 09:54:08AM -0300, [EMAIL PROTECTED] wrote:
> Hi All,
> 
>   Is it always safe to use "-funroll-loops" as a flag to 
> /etc/make.conf ? Does it realy improve the compiled programs?
> 
>   When should I avoid to use it?


If you are using gcc42 -funroll-loops can be a win. gcc3.x
is less savvy about knowing the limits of complexity to unroll
which loops.  I'm doing some tests with gcc34 (default) and
gcc42. The latter can yield significant improvements  iff
you know what you're doing.  It's no magic bullet.

gary


> 
> - Marcelo
> 
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-- 
  Gary Kline  [EMAIL PROTECTED]   www.thought.org  Public Service Unix

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Re: unroll-loops - Is it always safe?

2007-04-05 Thread Kris Kennaway 
On Thu, Apr 05, 2007 at 09:54:08AM -0300, [EMAIL PROTECTED] wrote:
> Hi All,
> 
>   Is it always safe to use "-funroll-loops" as a flag to 
> /etc/make.conf ? Does it realy improve the compiled programs?

No and usually not.

>   When should I avoid to use it?

You should never use it unless you have measured an improvement on
specific code.

Kris


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