Re: [PATCH] rs6000: Better error messages for power8/9-vector builtins

["Paul A. Clarke" <pc@us.ibm.com>]

On Wed, Nov 17, 2021 at 11:00:07AM -0600, Bill Schmidt via Gcc-patches wrote:
> On 11/17/21 10:54 AM, Paul A. Clarke wrote:
> > On Tue, Nov 16, 2021 at 11:12:35AM -0600, Bill Schmidt via Gcc-patches wrote:
> >> Hi!  During a previous patch review, Segher asked that I provide better
> >> messages when builtins are unavailable because they require both a minimum
> >> CPU and the enablement of VSX instructions.  This patch does just that.
> > ...
> >> gcc/
> >> 	* config/rs6000/rs6000-call.c (rs6000_invalid_new_builtin): Change
> >> 	error messages for ENB_P8V and ENB_P9V.
> >> ---
> >>  gcc/config/rs6000/rs6000-call.c | 6 ++++--
> >>  1 file changed, 4 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/gcc/config/rs6000/rs6000-call.c b/gcc/config/rs6000/rs6000-call.c
> >> index 85fec80c6d7..035266eb001 100644
> >> --- a/gcc/config/rs6000/rs6000-call.c
> >> +++ b/gcc/config/rs6000/rs6000-call.c
> >> @@ -11943,7 +11943,8 @@ rs6000_invalid_new_builtin (enum rs6000_gen_builtins fncode)
> >>        error ("%qs requires the %qs option", name, "-mcpu=power8");
> >>        break;
> >>      case ENB_P8V:
> >> -      error ("%qs requires the %qs option", name, "-mpower8-vector");
> >> +      error ("%qs requires the %qs and %qs options", name, "-mcpu=power8",
> >> +	     "-mvsx");
> > "-mcpu=power8" itself enables "-mvsx", doesn't it?
> 
> Of course, but it can be disabled with -mno-vsx.  Then you get this error.
> You won't get it unless you deliberately did something strange with the
> compile options.
> 
> >
> >>        break;
> >>      case ENB_P9:
> >>        error ("%qs requires the %qs option", name, "-mcpu=power9");
> >> @@ -11953,7 +11954,8 @@ rs6000_invalid_new_builtin (enum rs6000_gen_builtins fncode)
> >>  	     name, "-mcpu=power9", "-m64", "-mpowerpc64");
> >>        break;
> >>      case ENB_P9V:
> >> -      error ("%qs requires the %qs option", name, "-mpower9-vector");
> >> +      error ("%qs requires the %qs and %qs options", name, "-mcpu=power9",
> >> +	     "-mvsx");
> > Similarly, "-mcpu=power9" itself enables "-mvsx", doesn't it?
> >
> > Are you trying to also say "don't use -mno-vsx"?  If so, maybe s/and/with/
> > would be slightly less confusing? This is going to be awkward unless it can
> > be more precise, like two messages depending on actual context:
> > - with "-mcpu=power8 -mno-vsx:  "...requires -mvsx".
> > - without "-mcpu=power8":  "...requires -mcpu=power8".
> 
> This seems like a YMMV situation...I don't see the confusion myself.

I guess I'm being pedantic.  "requires -mcpu=power8 and -mvsx" is not
accurate from a user's point a view, as "-mcpu=power8" is sufficient,
since "-mvsx" is enabled when "-mcpu=power8" is specified.

The real "requires" is "-mcpu=power8" and no "-mno-vsx".

(I'm just picturing myself fumbling around in a Makefile written by
somebody else. ;-)

It's not a strong objection, since specifying "-mno-vsx" should be
uncommon.  (Right?)  And, specifying "-mcpu=power8 -mvsx" is harmless.

PC