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

[Paul Cercueil]

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...

Cheers,
-Paul

lightning_ppc.txt
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