Re: [PATCH] ppc: Fix 'calli' when floating-point arguments are passed

[Paulo César Pereira de Andrade]

Em qua., 7 de set. de 2022 às 07:09, Paul Cercueil
<paul@crapouillou.net> escreveu:
>
> Hi Paulo,
>
> Le mar., sept. 6 2022 at 09:43:06 -0300, Paulo César Pereira de
> Andrade <paulo.cesar.pereira.de.andrade@gmail.com> a écrit :
> > Em seg., 5 de set. de 2022 às 17:15, Paul Cercueil
> > <paul@crapouillou.net> escreveu:
> >>
> >>  Hi Paulo,
> >>  >
> >>  >   This is a not a very common pattern and found a bug in the
> >>  > computation of live registers static setup.
> >>  >   Please rebuild with the last git push, main difference is the
> >>  > change:
> >>  >
> >>  > -                       jit_regset_ior(&reglive, &reglive,
> >> &regmask);
> >>  > +                       jit_regset_ior(&block->reglive, &reglive,
> >>  > &regmask);
> >>  >
> >>  > The 2 extra return added in the patch is just to avoid extra
> >>  > computation
> >>  > that is not required, and avoids possible issues setting as live
> >>  > registers
> >>  > that are known dead.
> >>  >
> >>  >   The problem the git commit corrects is that it is setting only
> >> the
> >>  > local
> >>  > variable and exiting the function, without updating the initial
> >> state
> >>  > of the split block after the conditional branch.
> >>
> >>  I think it did something since now it doesn't crash at the same
> >> spot ;)
> >>
> >>  I get the same thing but with register r10 now. But since r10 is a
> >>  caller-saved register I believe this is expected, and I need a
> >>  jit_live() there.
> >>
> >>  If I add a jit_live(_R10) before the jit_jmpi() then everything
> >> works.
> >>  Thanks!
> >>
> >>  Note that I use _R10 in my code because I do need a caller-saved
> >>  register and none of the JIT_R/JIT_V are. I use it as a counter,
> >> and I
> >>  need to update it in Lightning-generated functions. If I use a
> >>  callee-saved register, Lightning will generate code to spill/reload
> >> the
> >>  register and I can't update it within functions.
> >
> >   To use _R10 you need to cheat a bit, as it is the register for the
> > 8th
> > argument.
> >   Please also note that with the last patch, now it does what it
> > was supposed to do before, that is to assume all callee save registers
> > are live once reaching a jump to an address it cannot determine :(
> > And if there isn't a free non callee save register, it will assert at
> > that
> > point, as it needs a temporary that cannot be spilled, because it does
> > not know the target, nor can added code to reload the register used
> > temporarily, if it did run out of registers.
>
> Sadly I still see a few problems. See the attached file.
>
> The problem is now that the second bswapr_ui() (after the L2 label)
> uses my callee-saved register r25 (aka. JIT_V2) as a temporary, while
> this register is live...

  Just to better understand, how is the:

    jmpi 0x20000d0c

generated? Just a plain jit_jmpi(ADDR); where ADDR is in a previously
generated jit?

  This must be supported for obvious reasons, but should avoid this
pattern as much as possible, as it basically breaks all the logic to
keep the live state of registers.

> Cheers,
> -Paul

Thanks,
Paulo