Re: RFA: Fix PR 33290 (fallout from Tweak optabs.c's use of constant rtx_costs)

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 9/3/07, Richard Sandiford <richard@codesourcery.com> wrote:
> This patch caused PR 33290, an ICE for PPC on execute/930921-1.c.
> The problem was with the new modes used when forcing constants
> into registers:
>
> Richard Sandiford <richard@codesourcery.com> writes:
> > +/* X is to be used in mode MODE as an operand to BINOPTAB.  If we're
> > +   optimizing, and if the operand is a constant that costs more than
> > +   1 instruction, force the constant into a register and return that
> > +   register.  Return X otherwise.  UNSIGNEDP says whether X is unsigned.  */
> > +
> > +static rtx
> > +avoid_expensive_constant (enum machine_mode mode, optab binoptab,
> > +                       rtx x, bool unsignedp)
> > +{
> > +  if (optimize
> > +      && CONSTANT_P (x)
> > +      && rtx_cost (x, binoptab->code) > COSTS_N_INSNS (1))
> > +    {
> > +      if (GET_MODE (x) != VOIDmode)
> > +     x = convert_modes (mode, VOIDmode, x, unsignedp);
> > +      x = force_reg (mode, x);
> > +    }
> > +  return x;
> > +}
> ...
> > +  /* If we are optimizing, force expensive constants into a register.  */
> > +  xop0 = avoid_expensive_constant (mode0, binoptab, xop0, unsignedp);
> > +  if (!shift_optab_p (binoptab))
> > +    xop1 = avoid_expensive_constant (mode1, binoptab, xop1, unsignedp);
>
> If an operand is a CONST_INT, it is interpreted in the mode of the
> optab result.  That's what happened with the original code, but this
> new code (intentionally) uses the mode required by the optab instead.
> Thus the mode we pass to avoid_expansive_constant may be different
> from the mode of the result, and we need to convert the integer
> accordingly.
>
> Patch bootstrapped & regression-tested on x86_64-linux-gnu,
> where it introduced no new failures.  Also tested by Andreas
> Tobler on PPC Darwin, and in testing by Dominique d'Humieres
> (thanks to both).  OK to install?
>

Ok.

Thanks,
Richard.

>
>
> gcc/
>         PR middle-end/33290
>         * optabs.c (avoid_expensive_constant): Canonicalize CONST_INTs
>         before forcing them into a register.