Re: [gentoo-dev] [ANN] CFLAGS Builder

["Paul de Vrieze" <pauldv@gentoo.org>]

David Nielsen said:
> The -mcpu flag is depricated in GCC 3.3 - and should not be used
anymore. So in all fairness it would be best not to record it's usage,
it might mislead some users.

The only depreciation I could find concerning mcpu is in the mips port,
where it might not me appropriate. For x86 architectures it is available
though and it also serves a needed option as it determines instruction
scheduling. The march option does not, the march option determines which
instructions are used. As scheduling for an architecture lower than the
instructions is pointless implying mcpu makes sense. It is perfectly legal
though to specify
CFLAGS="-march=pentium -mcpu=pentium4" This would create code that runs on
anything bigger than a pentium, but is optimally scheduled for the
pentium4 processor. Scheduling has become increasingly important with the
newer (pentium and further) processors as they have the ability to run
some (but not all) instructions paralel to eachother. A p4 though provides
more pipelines than a p1, so instructions need to be scheduled differently
to optimally use all pipelines.

Paul

-- 
Paul de Vrieze
Researcher
Mail: pauldv@cs.kun.nl
Homepage: http://www.devrieze.net


-- 
Paul de Vrieze
Researcher
Mail: pauldv@cs.kun.nl
Homepage: http://www.devrieze.net




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