[PATCH] Disable PowerPC pc-relative support until the code is checked in

Michael Meissner meissner@linux.ibm.com
Thu Jun 6 23:54:00 GMT 2019


On Thu, Jun 06, 2019 at 06:14:29PM -0500, Segher Boessenkool wrote:
> Hi Mike,
> 
> On Thu, Jun 06, 2019 at 06:42:16PM -0400, Michael Meissner wrote:
> > 2019-06-06  Michael Meissner  <meissner@linux.ibm.com>
> > 
> > 	* config/rs6000/rs6000-cpus.def (ISA_FUTURE_MASKS_SERVER): Delete
> > 	enabling -mprefixed-addr and -mpcrel by default.
> 
> Why disable prefixed-addr?

Convenience, but I could leave it in, since we don't yet have any prefixed
instruction support.

> > 	* config/rs6000/rs6000.c (rs6000_option_override_internal): Make
> > 	-mpcrel and -mprefixed-addr act like other swtiches (i.e. using
> 
> Typo ("switches").

Thanks.

> > 	-mpcrel automatically sets -mcpu=future and -mprefixed-addr, and
> 
> Automatically setting -mcpu= is a bad thing.  Instead, we should just
> error out if someone tries to use -mpcrel with a CPU (or ABI, etc.) that
> doesn't support it.  Or, is there any special reason you want it?

Well, I was trying to be consistant with the other things (-mpower9-vector
automaically sets all of the other power9 options).  If you feel we don't need
the consistancy, I can remove that part of the patch.

As I mentioned elsewhere, there is a real problem with options specified on the
command line and pragma/attribute target (basically if you set -mpcrel on the
command line, and then do '#pragma GCC target ("cpu=power9")', it will
currently complain that -mfuture or -mcpu=future is not set.  I wanted to do
the minimum patch so other people could start using the target.

> In the future, we will not have an -mprefixed-addr option (it will be
> always on for CPUs that support it), and I don't see any real reason
> to allow disabling pcrel either, but we'll see.

Well I suspect for at least several months we will need the ability to turn off
pc-relative support but allow the other future stuff.

-- 
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meissner@linux.ibm.com, phone: +1 (978) 899-4797



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