Re: Passing the complex args in the GPR's

[Michael Matz <matz@suse.de>]

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Hey,

On Tue, 6 Jun 2023, Umesh Kalappa via Gcc wrote:

> Question is : Why does GCC choose to use GPR's here and have any
> reference to support this decision  ?

You explicitely used -m32 ppc, so 
https://www.polyomino.org.uk/publications/2011/Power-Arch-32-bit-ABI-supp-1.0-Unified.pdf 
applies.  It explicitely states in "B.1 ATR-Linux Inclusion and 
Conformance" that it is "ATR-PASS-COMPLEX-IN-GPRS", and other sections 
detail what that means (namely passing complex args in r3 .. r10, whatever 
fits).  GCC adheres to that, and has to.

The history how that came to be was explained in the thread.


Ciao,
Michael.

 > 
> Thank you
> ~Umesh
> 
> 
> 
> On Tue, Jun 6, 2023 at 10:16 PM Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
> >
> > Hi!
> >
> > On Tue, Jun 06, 2023 at 08:35:22PM +0530, Umesh Kalappa wrote:
> > > Hi Adnrew,
> > > Thank you for the quick response and for PPC64 too ,we do have
> > > mismatches in ABI b/w complex operations like
> > > https://godbolt.org/z/bjsYovx4c .
> > >
> > > Any reason why GCC chose to use GPR 's here ?
> >
> > What did you expect, what happened instead?  Why did you expect that,
> > and why then is it an error what did happen?
> >
> > You used -O0.  As long as the code works, all is fine.  But unoptimised
> > code frequently is hard to read, please use -O2 instead?
> >
> > As Andrew says, why did you use -m32 for GCC but -m64 for LLVM?  It is
> > hard to compare those at all!  32-bit PowerPC Linux ABI (based on 32-bit
> > PowerPC ELF ABI from 1995, BE version) vs. 64-bit ELFv2 ABI from 2015
> > (LE version).
> >
> >
> > Segher
>