[PATCH, rs6000] Fixing PR 67145

[Segher Boessenkool]

On Fri, Feb 26, 2016 at 01:35:10PM -0800, Richard Henderson wrote:
> On 02/26/2016 01:03 PM, Segher Boessenkool wrote:
> > On Thu, Feb 25, 2016 at 09:08:32PM -0800, Richard Henderson wrote:
> >> +      /* Perform rematerialization if only all operands are registers and
> >> +         all operations are PLUS.  */
> >> +      for (i = 0; i < n_ops; i++)
> >> +	if (ops[i].neg || !REG_P (ops[i].op))
> >> +	  return NULL_RTX;
> >> +      goto gen_result;
> >> +    }
> > 
> > If you check for fixed registers as well here, does that work for you?
> 
> Maybe.  It prevents canonicalization of reg+fp vs fp+reg, which could well
> occur via arithmetic on locally allocated arrays.

Where are these canonicalization rules described?

> I guess for the purposes of stage4 I'd be willing to do
> 
>   if (ops[i].neg
>       || !REG_P (ops[i].op)
>       || (REGNO (ops[i].op) < FIRST_PSEUDO_REGISTER
>           && fixed_regs[REGNO (ops[i].op)]
>           && !global_regs[REGNO (ops[i].op)]
>           && ops[i].op != frame_pointer_rtx
>           && ops[i].op != arg_pointer_rtx
>           && ops[i].op != stack_pointer_rtx))
> 
> It's pretty ugly though, and I wouldn't want to keep this forever.

Yeah.

> The rs6000 change really ought to be evaluated at some point.  Given its scope,
> I see little difference to doing that now vs putting it off to gcc7.

It is stage 4.  This rs6000 change has almost 100% chance of introducing
regressions.


Segher