Re: [PATCH V2] Disable sched1 in functions that call setjmp

[Qing Zhao <qing.zhao@oracle.com>]

> On Dec 23, 2022, at 2:33 AM, Alexander Monakov <amonakov@ispras.ru> wrote:
> 
> 
> On Thu, 22 Dec 2022, Qing Zhao wrote:
> 
>>> I think scheduling across calls in the pre-RA scheduler is simply an oversight,
>>> we do not look at dataflow information and with 50% chance risk extending
>>> lifetime of a pseudoregister across a call, causing higher register pressure at
>>> the point of the call, and potentially an extra spill.
>> 
>> I am a little confused, you mean pre-RA scheduler does not look at the data flow
>> information at all when scheduling insns across calls currently?
> 
> I think it does not inspect liveness info, and may extend lifetime of a pseudo
> across a call, transforming
> 
>  call foo
>  reg = 1
>  ...
>  use reg
> 
> to
> 
>  reg = 1
>  call foo
>  ...
>  use reg
> 
> but this is undesirable, because now register allocation cannot select a
> call-clobbered register for 'reg’.
Okay, thanks for the explanation.

Then, why not just check the liveness info instead of inhibiting all scheduling across calls?

Qing
> 
> Alexander