"juzhe.zh...@rivai.ai" <juzhe.zh...@rivai.ai> writes:
> I think it's reasonable refactor reduction instruction pattern work around
> this issue.
>
> Going to send a patch to apply this solution.
>
> So drop this patch. Sorry for bothering Richard S.
It wasn't a bother.
On the patch: as things stand, we try to make the use_info's mode be
at least as big as all the uses in the instruction. So if we did
want to handle unordered modes for hard registers, I think we would need
to fall back on the register's natural mode instead. I did something
similar in LRA recently for PR112278 (6e2e0ce6795).
So if in future you would like to change RTL-SSA, a fix along those
lines would be fine with me.
Thanks,
Richard
>
>
>
> juzhe.zh...@rivai.ai
>
> From: Robin Dapp
> Date: 2023-12-11 17:01
> To: Juzhe-Zhong; gcc-patches
> CC: rdapp.gcc; richard.sandiford
> Subject: Re: [PATCH] RTL-SSA: Fix ICE on record_use of RTL_SSA for RISC-V
> VSETVL PASS
>> In record_use:
>>
>> if (HARD_REGISTER_NUM_P (regno)
>> && partial_subreg_p (use->mode (), mode))
>>
>> Assertion failed on partial_subreg_p which is:
>>
>> inline bool
>> partial_subreg_p (machine_mode outermode, machine_mode innermode)
>> {
>> /* Modes involved in a subreg must be ordered. In particular, we must
>> always know at compile time whether the subreg is paradoxical. */
>> poly_int64 outer_prec = GET_MODE_PRECISION (outermode);
>> poly_int64 inner_prec = GET_MODE_PRECISION (innermode);
>> gcc_checking_assert (ordered_p (outer_prec, inner_prec));
>> -----> cause ICE.
>> return maybe_lt (outer_prec, inner_prec);
>> }
>>
>> RISC-V VSETVL PASS is an advanced lazy vsetvl insertion PASS after RA
>> (register allocation).
>>
>> The rootcause is that we have a pattern (reduction instruction) that
>> includes both VLA (length-agnostic) and VLS (fixed-length) modes.
>
> Maybe as additional context: The second input (which has a VLA mode here)
> is not used entirely but just its first element. This serves as initial
> value for the reduction.
>
> I'm not sure we'd want to model it as subreg here (endianness etc?).
> Could we have a VLS-mode equivalent for the VLA mode that only holds
> one element?
>
> Regards
> Robin
>
>
