Re: Mips delay slot optimization

[Paulo César Pereira de Andrade]

Em sex., 24 de fev. de 2023 às 08:08, Paul Cercueil
<paul@crapouillou.net> escreveu:
>
> Hi Paulo,

  Hi Paul,

> Le jeudi 23 février 2023 à 13:34 -0300, Paulo César Pereira de Andrade
> a écrit :
> >  Hi Paul,
> >
> >   I wrote a new logic to optimize delay slot usage for the mips port.
> >
> >  It was broken for mips6_p() anyway, so now there is  basically a
> > full decoder to check if an instruction can be added to the delay
> > slot,
> > and a few new helpers to it.
> >
> >   A basic documentation of how it works is in the commit changelog.
> >
> >   I want to believe it is far more complete than your previous set of
> > patches, and it also forces adding extra logic to the decoder if
> > implementing new lightning functionality.
> >
> >   To disable it in a hacky mode, just change instr() to never keep
> > a pending() instruction.
> >
> >   Please let me know if you see any regressions, or if somehow it
> > is missing some delay slot usage optimization that was done in
> > your patches.

  It was a really very large change, and it would be easy to get regressions.

  The new patch is far more aggressive, and relies in both, correct usage
of jit_get_reg_for_delay_slot(), flush(), pending() and delay(), as well as
jit_get_reg_for_delay_slot() correctly decoding the instruction and
internally calling flush() if even if getting a valid register, still moving the
'pending()' instruction to the delay slot would cause a problem.

> There are definitely regressions, my emulator just hangs when running
> 8032a68, while 2.2.1 worked fine.

  Please try first with 8e5ba87. I did a new review of the patches, and
found a major logic error in jmpi. It was passing "make check" in different
test environments, but was by accident, surely soon or later the bug
would arise.

> If I can find some time I will try to generate a small program that
> reproduces the problem.
>
> Cheers,
> -Paul

Thanks!
Paulo