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Re: Combine four insns


On 08/06/2010 05:07 PM, Steven Bosscher wrote:
On Fri, Aug 6, 2010 at 4:48 PM, Bernd Schmidt<bernds@codesourcery.com> wrote:
I'd argue that compile-time shouldn't be our top priority, as it's one
of the few things that still benefits from Moore's Law, while the same
may not be true for the programs we compile.  I expect people will argue
a 1% slowdown is unacceptable, but in that case I think we need to
discuss whether users are complaining about slow compiles more often
than they complain about missed optimizations - in my experience the
reverse is true.

It depends where you look. In the free software community, the majority of complaints is about compile time, but perhaps for your customers the missed optimizations are more important.

But perhaps the optimization can be performed in another place than
combine? If it's just a relatively small set of common patterns, a
quick GIMPLE pass may be preferable.

(I know, it's the old argument we've had before: You have a real fix
now for a real problem, others (incl. me) believe that to fix this
problem in combine is a step away from sane instruction selection that
GCC may not have for years to come...)

In this case I actually think this argument is not going to work, since we have not even a prototype of a sane instruction selection pass and not even someone who is thinking about working on it.


Paolo


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