[PATCH] Do not allow target_clones with alias attr (PR lto/90500).

[Richard Biener]

On Thu, May 16, 2019 at 1:38 PM Martin Liška <mliska@suse.cz> wrote:
>
> On 5/16/19 1:24 PM, Richard Biener wrote:
> > On Thu, May 16, 2019 at 1:18 PM Martin Liška <mliska@suse.cz> wrote:
> >>
> >> Hi.
> >>
> >> We should not allow target_clones being combined with alias attribute.
> >>
> >> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
> >>
> >> Ready to be installed?
> >
> > So that's because an alias cannot be turned into a dispatcher and still
> > be an alias, correct?  So a way around this would be to turn the
> > alias into the dispatcher and clone the alias target, leaving the
> > plain alias target as default variant not going through the dispatcher?
>
> We do allow having an alias to a target clone symbol:
>
> __attribute__((target_clones("arch=haswell", "default"))) int __tanh() {}
> __typeof(__tanh) tanhf64 __attribute__((alias("__tanh")));
>
> Having that tanhf64 points to the resolver, which I believe is correct.

In this case yes.  I think the case in the PR wants to have an alias
to the default variant instead and that's not possible so it tries to
do the cloning on an alias (basically tell cloning to use an alternate
symbol name for the resolver, leaving the default in place).  IMHO
a reasonable feature, not sure if a reasonable way to achieve.

> The PR is about an alias that has itself target_clone attribute, which
> does not make sense.
>
> >
> > Of course in the testcase the body of the alias target isn't available
> > but that's a general issue, not special to aliases?
>
> We do the target_clone expansion just for node->definition which is true
> for node->alias == true symbols.

I see.  I guess it should be done for node->analyzed only, but yes,
w/o considering aliases or thunks all definitions have bodies.

Richard.

> Martin
>
> >
> > Richard.
> >
> >> Thanks,
> >> Martin
> >>
> >> gcc/ChangeLog:
> >>
> >> 2019-05-16  Martin Liska  <mliska@suse.cz>
> >>
> >>         PR lto/90500
> >>         * multiple_target.c (expand_target_clones): Do not allow
> >>         target_clones being used with a symbol that is an alias.
> >>
> >> gcc/testsuite/ChangeLog:
> >>
> >> 2019-05-16  Martin Liska  <mliska@suse.cz>
> >>
> >>         PR lto/90500
> >>         * gcc.target/i386/pr90500-1.c: New test.
> >>         * gcc.target/i386/pr90500-2.c: New test.
> >> ---
> >>  gcc/multiple_target.c                     | 5 ++++-
> >>  gcc/testsuite/gcc.target/i386/pr90500-1.c | 8 ++++++++
> >>  gcc/testsuite/gcc.target/i386/pr90500-2.c | 7 +++++++
> >>  3 files changed, 19 insertions(+), 1 deletion(-)
> >>  create mode 100644 gcc/testsuite/gcc.target/i386/pr90500-1.c
> >>  create mode 100644 gcc/testsuite/gcc.target/i386/pr90500-2.c
> >>
> >>
>