Thanks Richard.
Committed with V2:
https://gcc.gnu.org/pipermail/gcc-patches/2023-December/640172.html
juzhe.zh...@rivai.ai
From: Richard Sandiford
Date: 2023-12-11 20:12
To: juzhe.zhong\@rivai.ai
CC: Robin Dapp; gcc-patches
Subject: Re: [PATCH] RTL-SSA: Fix ICE on record_use of RTL_SSA for RISC-V
VSETVL PASS
"juzhe.zh...@rivai.ai" <juzhe.zh...@rivai.ai> writes:
> Thanks Richard.
>
> It would be great if you are ok I can fix it in RTL_SSA.
> I leverage your LRA patch in RTL_SSA:
>
> else
> {
> // Record the mode of the largest use. The choice is arbitrary if
> // the instruction (unusually) references the same register in two
> // different but equal-sized modes.
> gcc_checking_assert (use->insn () == insn);
> if (HARD_REGISTER_NUM_P (regno))
> {
> if (!ordered_p (GET_MODE_PRECISION (use->mode ()),
> GET_MODE_PRECISION (mode)))
> use->set_mode (reg_raw_mode[regno]);
> else if (partial_subreg_p (use->mode (), mode))
> use->set_mode (mode);
> }
> use->record_reference (ref, false);
> }
>
> Is it reasonable to you ?
Yeah, the above is OK for trunk, thanks.
Richard
>
> Thanks.
>
>
> juzhe.zh...@rivai.ai
>
> From: Richard Sandiford
> Date: 2023-12-11 19:45
> To: juzhe.zhong\@rivai.ai
> CC: Robin Dapp; gcc-patches
> Subject: Re: [PATCH] RTL-SSA: Fix ICE on record_use of RTL_SSA for RISC-V
> VSETVL PASS
> "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
>>
>>
>
