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Re: Patch config.gcc to accept --with-cpu=85xx for PowerPC
- From: Geoff Keating <geoffk at desire dot geoffk dot org>
- To: eager at mvista dot com
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Fri, 14 May 2004 12:21:01 -0700
- Subject: Re: Patch config.gcc to accept --with-cpu=85xx for PowerPC
- References: <40A3E486.firstname.lastname@example.org> <email@example.com> <40A5017F.firstname.lastname@example.org>
> X-Original-To: email@example.com
> Date: Fri, 14 May 2004 10:27:27 -0700
> From: Michael Eager <firstname.lastname@example.org>
> Organization: MontaVista Software
> X-Accept-Language: en-us, en
> Cc: email@example.com
> X-OriginalArrivalTime: 14 May 2004 17:14:35.0140 (UTC) FILETIME=[EDF72C40:01C439D6]
> Geoff Keating wrote:
> > Michael Eager <firstname.lastname@example.org> writes:
> >>The attached patch makes gcc configure correctly with
> >>--target=powerpc-unknown-linux and --with-cpu=8540. This is the
> >>same as --target=powerpc-unknown-linux-spe.
> > It's the same as using --target=powerpc-linux and then using
> > -mcpu=8540, which does not trigger the SPE ABI, and is therefore not
> > the same as powerpc-unknown-linux-spe. The patch is not OK.
> In the patch, linuxspe.h is appended to the tm header list when
> configured with --with-cpu=8540. So it should configure exactly the
> same as powerpc-unknown-linux-spe.
Yes. That's why the patch was rejected.
> >>PowerPC seems to append model specific features to the target
> >>tuple (eg, altivec, spe). IMO, these features should be handled
> >>dynamically (as they often are) or at worst, by testing --with-cpu in
> > These aren't "model specific features", they are ABI specifications.
> I guess that's a matter of viewpoint. Not having FP regs seems to me
> to be a processor characteristic, not an ABI characteristic.
No, it's really not a matter of viewpoint. I did not mean 'they look
like ABI specifications', I meant 'they specify the ABI'.
> Specifying --target=powerpc-linux and -mcpu=8540 generates code which
> is incorrect for the 8540, because it uses FP instructions.
According to the table in rs6000_override_options, the 8540 *does*
have FP instructions. If it doesn't, that's a bug. Patches to fix
that are welcome.
> As for ABI differences, other arch's handle this with -mabi, not
> different configuration. (I'm not always happy with the muddle
> of MIPS mcpu/mtune/march/mabi, but at least I don't have to configure
> gcc differently for each version.)
rs6000 handles this with -mabi, too, but that wasn't implemented for
the SPE work. Patches to fix that are welcome, too.
- Geoffrey Keating <email@example.com>