RE: [PATCH] rs6000: Canonicalize copysign (x, -1) back to -abs (x) in the backend [PR112606]

[Tamar Christina <Tamar.Christina@arm.com>]

> -----Original Message-----
> From: Jakub Jelinek <jakub@redhat.com>
> Sent: Monday, November 27, 2023 8:13 AM
> To: Tamar Christina <Tamar.Christina@arm.com>
> Cc: Xi Ruoyao <xry111@xry111.site>; Segher Boessenkool
> <segher@kernel.crashing.org>; David Edelsohn <dje.gcc@gmail.com>; gcc-
> patches@gcc.gnu.org; Andrew Pinski <apinski@marvell.com>
> Subject: Re: [PATCH] rs6000: Canonicalize copysign (x, -1) back to -abs (x) in
> the backend [PR112606]
> 
> On Mon, Nov 27, 2023 at 07:55:52AM +0000, Tamar Christina wrote:
> > > For POPCOUNT I've introduced recently a way to provide custom
> > > expand_* function and decide there what optimizations to use, even
> > > when it otherwise is an integral unary optab ifn.
> > >
> >
> > Oh that sounds interesting, do you have a commit for me to look at? I
> > couldn't Spot anything obvious in the history.
> 
> https://gcc.gnu.org/r14-5613

Oh, that's nice! If that's the case a simpler fix could be to let COPYSIGN become
one of these as well, and then just have PPC do a FAIL on the abs and neg cases.

Expand_copysign already does the fneg (fabs ()) rewriting if the target rejects the
optab through expand_copysign_absneg

That would also fix the i386 and Arm assembly scan failures and te phi-opts case
when the IFN isn't available.. I can do that if you prefer? Since those are on my list
to fix anyway.

Thanks,
Tamar

> 
> 	Jakub