Re: [PATCH] simplify-rtx: Fix VOIDmode operand handling in simplify_subreg [PR108805]

[Richard Sandiford <richard.sandiford@arm.com>]

Uros Bizjak <ubizjak@gmail.com> writes:
> On Fri, Feb 17, 2023 at 8:38 AM Richard Biener <rguenther@suse.de> wrote:
>>
>> On Thu, 16 Feb 2023, Uros Bizjak wrote:
>>
>> > simplify_subreg can return VOIDmode const_int operand and will
>> > cause ICE in simplify_gen_subreg when this operand is passed to it.
>> >
>> > The patch prevents VOIDmode temporary from entering simplify_gen_subreg.
>> > We can't process const_int operand any further, since outermode
>> > is not an integer mode here.
>>
>> But if it's a CONST_INT then we know it's of int_outermode, no? That is,
>> doesn't simplify_subreg (mode, ...) always return something in 'mode'
>> and thus we can always pass just 'mode' as third argument to the
>> following simplify_gen_subreg call?
>
> You are right. I am testing the attached patch that works too.

Thanks for this, it's the correct fix.  But as noted in
https://gcc.gnu.org/pipermail/gcc-patches/2023-January/610920.html,
the final 0 is also wrong for big-endian.  Andre?

Richard

>
> Uros.
>
> diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
> index 0a1dd88b0a8..3955929bb70 100644
> --- a/gcc/simplify-rtx.cc
> +++ b/gcc/simplify-rtx.cc
> @@ -7665,7 +7665,7 @@ simplify_context::simplify_subreg (machine_mode outermode, rtx op,
>      {
>        rtx tem = simplify_subreg (int_outermode, op, innermode, byte);
>        if (tem)
> -	return simplify_gen_subreg (outermode, tem, GET_MODE (tem), 0);
> +	return simplify_gen_subreg (outermode, tem, int_outermode, 0);
>      }
>  
>    /* If OP is a vector comparison and the subreg is not changing the