[PATCH 1/1] RISC-V: Support ".option [no]exact" assembler directives

[Tsukasa OI]

On 2025/05/16 18:12, Jan Beulich wrote:
> On 16.05.2025 11:00, Tsukasa OI wrote:
>> On 2025/05/16 15:38, Jan Beulich wrote:
>>> Looks quite okay to me. I'm not entirely certain we need the new insn flag, but
>>> perhaps it's good to do it this way to also cover the doc aspect (i.e. making
>>> explicit which aliases are which).
>>
>> Thanks.
>>
>> The intent of the new instruction flag is, we don't want to disable all
>> aliases but only aliases which will have unintended side effects in the
>> context of the exact mode (currently, this flag is applied to RVC
>> aliases which will change the instruction length from the non-RVC _main_
>> encoding).
>>
>> For instance, we want to disable aliases of "addi" / "add" (that turn
>> into compressed instructions like "c.addi") in the exact mode but we
>> _don't_ want to disable "sgt" (set if greater than) aliases because
>> "sgt" only turns into "sle" (set if less than or equal; with two source
>> operands flipped) and unintended side effects in the context of the
>> exact mode will not occur.
>>
>> For documentation, let me consider.  I think the best place to
>> improve/describe is at the definition of INSN_NON_EXACT, right?
> 
> I'm sorry if I caused confusion - I didn't mean to ask for anything to be
> added.

Ah, looking now, I think the description of INSN_NON_EXACT is too brief
to decide when to use and I want to add (at least) DOs and DON'Ts.

And, I found a clear bug and a border case while reviewing my patch set.
 So, I thought it's a good time to reconsider.

1.  "unimp" (compressed alias) lacks INSN_NON_EXACT and must be added.
2.  Decide whether we add INSN_NON_EXACT to non-compressed
    aliases of "zext.[wh]" (likely to keep as-is).

>>> The only other (more general) comment I'd
>>> have is: For boolean fields in struct riscv_set_options, can't we start using
>>> bool?
>>
>> I completely agree that and I think even regular bool is wasteful.
>> So after the improved version of this patch set is applied, I have a
>> plan to submit a patch to change GAS RISC-V option struct members from
>> "int OPTION;" to "bool OPTION : 1;" (using bit fields).
> 
> Yes please.
> 
> Jan
> 

Thanks,
Tsukasa