Re: [PATCH v2] rs6000: Stackoverflow in optimized code on PPC [PR100799]

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Apr 02, 2024 at 02:12:04PM +0800, Kewen.Lin wrote:
> >>>> The old code for the unused hidden parameter (which was the 9th param) would
> >>>> fall thru to the "return NULL_RTX;" which would make the callee assume there
> >>>> was a parameter save area allocated.  Now instead, we'll return a reg rtx,
> >>>> probably of r11 (r3 thru r10 are our param regs) and I'm guessing we'll now
> >>>> see a copy of r11 into a pseudo like we do for the other param regs.
> >>>> Is that a problem? Given it's an unused parameter, it'll probably get deleted
> >>>> as dead code, but could it cause any issues?  What if we have more than one
> 
> I think Peter raised one good point, not sure it would really cause some issues,
> but the assigned reg goes beyond GP_ARG_MAX_REG, at least it is confusing to people
> especially without DCE like at -O0.  Can we aggressively remove these candidates
> from DECL_ARGUMENTS chain?  Does it cause any assertion to fail?

I'd prefer not to remove DECL_ARGUMENTS chains, they are valid arguments that just some
invalid code doesn't pass.  By removing them you basically always create an
invalid case, this time in the other direction, valid caller passes more
arguments than the callee (invalidly) expects.

	Jakub