Re: Combine four insns

[Bernd Schmidt <bernds@codesourcery.com>]

On 08/09/2010 04:50 PM, Mark Mitchell wrote:

> Also, I think that the number of instructions combine should consider
> might as well be a --param.  As far as I can tell, it would be
> reasonably easy to modify the pass to pass around an array of
> instructions to combine, rather than i0, i1, i2, i3.  Then, distributors
> could set whatever default (2, 3, 4, 5, 100, whatever) they think
> appropriate for their users.  Bernd, is this something that you could do
> readily?

Not readily since it would require rather more surgery to make sure all
the lifetimes, register deaths etc. are tracked.  Also, the way combine
keeps track of LOG_LINKS (i.e. single-basic block only, one user for
each reg only) makes larger windows have dubious value.

What I do want to try is to do something similar with fwprop (i.e. if
substitution fails or is unprofitable, try substituting more uses).  If
that turns out feasible, it should be possible to have it controlled by
a param.

> Like Bernd, I doubt that compilation time with optimization enabled per
> se is the dominant concern for most people.  GCC's own build times are
> increasingly dominated by configure scripts, make overhead, and linking.

I've been noticing fixincludes too.


Bernd