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Re: Dumb register allocation (PPC)



On Sunday, May 12, 2002, at 04:54 PM, David Edelsohn wrote:

> 	Please see the
>
> Trivial code generation stupidity thread:
> http://gcc.gnu.org/ml/gcc/2001-12/msg00907.html
>
> which evolved into the
> cant_combine_insn_p hard_reg->reg moves thread:
> http://gcc.gnu.org/ml/gcc/2001-12/msg01283.html
>
> This is a general difficulty of GCC handling argument registers.  The new
> register alloctor will allow us to start addressing it.

FWIW, I've got the check in cant_combine_insn_p
conditionalized on if(SMALL_REGISTER_CLASSES), and
everything works fine on ppc, and the code does improve.
If you look back at the thread when this patch went in:
http://gcc.gnu.org/ml/gcc-patches/2000-11/msg01466.html
you'll see there was some discussion of doing what I did,
but Jan Hubicka claimed improvements with the patch
even on non-SRC machines so it didn't go in that way;
but this patch is not a win on ppc according to my
measurements.  I haven't bothered submitting this
given jh's results and the firmness of rth's opinion
in the thread you quote, but I could.


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