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Re: cosmetic change - simplify cse.c:preferable()
- From: Richard Guenther <rguenther at suse dot de>
- To: Dodji Seketeli <dodji at seketeli dot org>
- Cc: Dimitrios Apostolou <jimis at gmx dot net>, gcc-patches at gcc dot gnu dot org, Andrey Belevantsev <abel at ispras dot ru>, Richard Henderson <rth at redhat dot com>
- Date: Thu, 19 Jul 2012 10:38:33 +0200 (CEST)
- Subject: Re: cosmetic change - simplify cse.c:preferable()
- References: <alpine.LNX.2.02.1207081038340.4288@localhost.localdomain> <m3bojcq2t2.fsf@seketeli.org>
On Wed, 18 Jul 2012, Dodji Seketeli wrote:
> Hey Dimitrios,
>
> I can't say much about your patch, so I am CC-ing the maintainers.
I don't think it's any good or clearer to understand.
Richard.
> Thanks.
>
> Dimitrios Apostolou <jimis@gmx.net> a ?crit:
>
> > Hello,
> >
> > I've had this patch some time now, it's simple and cosmetic only, I
> > had done it while trying to understand expression costs in CSE. I
> > think it's more readable than the previous one. FWIW it passed all
> > tests on x86.
> >
> >
> > Thanks,
> > Dimitris
> >
> > === modified file 'gcc/cse.c'
> > --- gcc/cse.c 2012-06-15 09:22:00 +0000
> > +++ gcc/cse.c 2012-07-08 07:28:52 +0000
> > @@ -713,32 +713,25 @@ approx_reg_cost (rtx x)
> > static int
> > preferable (int cost_a, int regcost_a, int cost_b, int regcost_b)
> > {
> > - /* First, get rid of cases involving expressions that are entirely
> > - unwanted. */
> > - if (cost_a != cost_b)
> > - {
> > - if (cost_a == MAX_COST)
> > - return 1;
> > - if (cost_b == MAX_COST)
> > - return -1;
> > - }
> > + int cost_diff = cost_a - cost_b;
> > + int regcost_diff = regcost_a - regcost_b;
> >
> > - /* Avoid extending lifetimes of hardregs. */
> > - if (regcost_a != regcost_b)
> > + if (cost_diff != 0)
> > {
> > - if (regcost_a == MAX_COST)
> > - return 1;
> > - if (regcost_b == MAX_COST)
> > - return -1;
> > + /* If none of the expressions are entirely unwanted */
> > + if ((cost_a != MAX_COST) && (cost_b != MAX_COST)
> > + /* AND only one of the regs is HARD_REG */
> > + && (regcost_diff != 0)
> > + && ((regcost_a == MAX_COST) || (regcost_b == MAX_COST))
> > + )
> > + /* Then avoid extending lifetime of HARD_REG */
> > + return regcost_diff;
> > +
> > + return cost_diff;
> > }
> >
> > - /* Normal operation costs take precedence. */
> > - if (cost_a != cost_b)
> > - return cost_a - cost_b;
> > - /* Only if these are identical consider effects on register pressure. */
> > - if (regcost_a != regcost_b)
> > - return regcost_a - regcost_b;
> > - return 0;
> > + /* cost_a == costb, consider effects on register pressure */
> > + return regcost_diff;
> > }
> >
> > /* Internal function, to compute cost when X is not a register; called
> >
>
>
--
Richard Guenther <rguenther@suse.de>
SUSE / SUSE Labs
SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746
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