Re: new unroller vs ppc

[Jan Hubicka <jh at suse dot cz>]

> Hello,
> 
> > Zdenek> Does this patch:
> > Zdenek> http://gcc.gnu.org/ml/gcc-patches/2003-03/msg01564.html
> > Zdenek> help?
> > 
> > 	No, not really:
> [snip]
> 
> looking at the assembler that comes out of crosscompiler, I see two
> problems:
> 
> 1) we do not do induction variable splitting; the webizer pass
>    http://gcc.gnu.org/ml/gcc-patches/2003-02/msg00501.html
>    should take care of this

This patch appears to have problems to get in, however I hope it will
one day.  Or is there something particulary wrong about it?

> 2) this code in cse.c
> 
> /* Don't associate these operations if they are a PLUS with the
>    same constant and it is a power of two.  These might be doable
>    with a pre- or post-increment.  Similarly for two subtracts of
>    identical powers of two with post decrement.  */
> 
>   if (code == PLUS && INTVAL (const_arg1) == INTVAL (inner_const)
>       && ((HAVE_PRE_INCREMENT
>            && exact_log2 (INTVAL (const_arg1)) >= 0)
>           || (HAVE_POST_INCREMENT
>               && exact_log2 (INTVAL (const_arg1)) >= 0)
>           || (HAVE_PRE_DECREMENT
>               && exact_log2 (- INTVAL (const_arg1)) >= 0)
>           || (HAVE_POST_DECREMENT
>               && exact_log2 (- INTVAL (const_arg1)) >= 0)))
>     break;
> 
> prevents us from combining the increments of induction variables even
> with webizer.  I think the correct solution is to split
> pre/post modify transformation out of flow.c (relatively easy,
> I have the patch somewhere), to run it before cse and to cancel this
> code.
You won't be able to cancel it completely I guess, only for CSE2 pass.
The passes before flow don't expect autoincrements to happen.
Otherwise this sounds like sane plan to me.

Honza
> 
> Zdenek