Re: [PATCH 0/7] ira/lra: Support subreg coalesce

[Lehua Ding <lehua.ding@rivai.ai>]

On 2023/11/10 18:16, Richard Sandiford wrote:
> Lehua Ding <lehua.ding@rivai.ai> writes:
>> Hi Richard,
>>
>> On 2023/11/8 17:40, Richard Sandiford wrote:
>>> Tracking subreg liveness will sometimes expose dead code that
>>> wasn't obvious without it.  PR89606 has an example of this.
>>> There the dead code was introduced by init-regs, and there's a
>>> debate about (a) whether init-regs should still be run and (b) if it
>>> should still be run, whether it should use subreg liveness tracking too.
>>>
>>> But I think such dead code is possible even without init-regs.
>>> So for the purpose of this series, I think the init-regs behaviour
>>> in that PR creates a helpful example.
>>
>> Yes, I think the init-regs should be enhanced to reduce unnecessary
>> initialization. My previous internal patchs did this in a separate
>> patch. Maybe I should split the live_subreg problem out of the second
>> patch and not couple it with these patches. That way it can be reviewed
>> separately.
> 
> But my point was that this kind of dead code is possible even without
> init-regs.  So I think we should have something that removes the dead
> code.  And we can try it on that PR (without changing init-regs).

Got it, so we should add a fast remove dead code job after init-regs pass.

-- 
Best,
Lehua (RiVAI)
lehua.ding@rivai.ai