Re: [r13-7135 Regression] FAIL: gcc.dg/vect/vect-simd-clone-18f.c scan-tree-dump-times vect "[\\n\\r] [^\\n]* = foo\\.simdclone" 2 on Linux/x86_64

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Apr 13, 2023 at 4:25 PM Andre Vieira (lists)
<andre.simoesdiasvieira@arm.com> wrote:
>
>
>
> On 13/04/2023 15:00, Richard Biener wrote:
> > On Thu, Apr 13, 2023 at 3:00 PM Andre Vieira (lists) via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> >>
> >>
> >>
> >> On 13/04/2023 11:01, Andrew Stubbs wrote:
> >>> Hi Andre,
> >>>
> >>> I don't have a cascadelake device to test on, nor any knowledge about
> >>> what makes it different from regular x86_64.
> >>
> >> Not sure you need one, but yeah I don't know either, it looks like it
> >> fails because:
> >> in-branch vector clones are not yet supported for integer mask modes.
> >>
> >> A quick look tells me this is because mask_mode is not VOIDmode.
> >> i386.cc's TARGET_SIMD_CLONE_COMPUTE_VECSIZE_AND_SIMDLEN will set
> >> mask_mode to either DI or SI mode when TARGET_AVX512F. So I suspect
> >> cascadelake is TARGET_AVX512F.
> >>
> >> This is where I bail out as I really don't want to dive into the target
> >> specific simd clone handling of x86 ;)
> >>
> >>>
> >>> If the cascadelake device is supposed to work the same as other x86_64
> >>> devices for these vectors then the test has found a bug in the compiler
> >>> and you should be looking to fix that, not fudge the testcase.
> >>>
> >>> Alternatively, if the device's capabilities really are different and the
> >>> tests should behave differently, then the actual expectations need to be
> >>> encoded in the dejagnu directives. If you can't tell the difference by
> >>> looking at the "x86_64*-*-*" target selector alone then the correct
> >>> solution is to invent a new "effective-target" selector. There are lots
> >>> of examples of using these throughout the testsuite (you could use
> >>> dg-require-effective-target to disable the whole testcase, or just use
> >>> the name in the scan-tree-dump-times directive to customise the
> >>> expectations), and the definitions can be found in the
> >>> lib/target-supports.exp and lib/target-supports-dg.exp scripts. Some are
> >>> fixed expressions and some run the compiler to probe the configuration,
> >>> but in this case you probably want to do something with "check-flags".
> >>
> >> Even though I agree with you, I'm not the right person to do this
> >> digging for such target specific stuff. So for now I'd probably suggest
> >> xfailing this for avx512f.
> >>>
> >>> For the unroll problem, you can probably tweak the optimization options
> >>> to disable that, the same as has been done for the epilogues feature
> >>> that had the same problem.
> >>
> >> I mistaken the current behaviour for unrolling, it's actually because of
> >> a latent bug. The vectorizer calls `vect_get_smallest_scalar_type` to
> >> determine the vectype of a stmt. For a function like foo, that has the
> >> same type (long long) everywhere this wouldn't be a problem, however,
> >> because you transformed it into a MASK_CALL that has a function pointer
> >> (which is 32-bit in -m32) that now becomes the 'smallest' type.
> >>
> >> This is all a red-herring though, I don't think we should be calling
> >> this function for potential simdclone calls as the type on which the
> >> veclen is not necessarily the 'smallest' type. And some arguments (like
> >> uniform and linear) should be ignored anyway as they won't be mapped to
> >> vectors.  So I do think this might have been broken even before your
> >> changes, but needs further investigation.
> >>> Since these are new tests for a new feature, I don't really understand
> >>> why this is classed as a regression?
> >>>
> >>> Andrew
> >>>
> >>> P.S. there was a commit to these tests in the last few days, so make
> >>> sure you pull that before making changes.
> >>
> >> The latest commit to these tests was mine, it's the one Haochen is
> >> reporting this regression against. My commit was to fix the issue richi
> >> had introduced that was preventing the feature you introduced from
> >> working. The reason nobody noticed was because the tests you introduced
> >> didn't actually test your feature, since you didn't specify 'inbranch'
> >> the omp declare simd pragma was allowing the use of not-inbranch simd
> >> clones and the vectorizer was being smart enough to circumvent the
> >> conditional and was still able to use simdclones (non inbranch ones) so
> >> when the inbranch stopped working, the test didn't notice.
> >>
> >> The other changes to this test were already after the fix for 108888
> >> that broke the inbranch feature you added, and so it was fixing a
> >> cascadelake testism but for the not-inbranch simdclones. So basically
> >> fixing a testism of a testism :/
> >>
> >>
> >> I am working on simdclone's for AArch64 for next Stage 1 so I don't mind
> >> looking at the issue with the vectype being chosen wrongly, as for the
> >> other x86 specific testisms I'll leave them to someone else.
> >
> > Btw, the new testsuite FAILs could be just epiloge vectorizations, so
> > maybe try the usual --param vect-epilogues-nomask=0 ...
> It already has those, Jakub added them.
>
> But that's not it, I've been looking at it, and there is code in place
> that does what I expected which is defer the choice of vectype for simd
> clones until vectorizable_simd_clone_call, unfortunately it has a
> mistaken assumption that simdclones don't return :/

I think that's not it - when the SIMD clone returns a vector we have to
determine the vector type in this function.  We cannot defer this.

> see vect_get_vector_types_for_stmt:
> ...
>    if (gimple_get_lhs (stmt) == NULL_TREE
>        /* MASK_STORE has no lhs, but is ok.  */
>        && !gimple_call_internal_p (stmt, IFN_MASK_STORE))
>      {
>        if (is_a <gcall *> (stmt))
>          {
>            /* Ignore calls with no lhs.  These must be calls to
>               #pragma omp simd functions, and what vectorization factor
>               it really needs can't be determined until
>               vectorizable_simd_clone_call.  */
>            if (dump_enabled_p ())
>              dump_printf_loc (MSG_NOTE, vect_location,
>                               "defer to SIMD clone analysis.\n");
>            return opt_result::success ();
>          }
>
>        return opt_result::failure_at (stmt,
>                                       "not vectorized: irregular
> stmt.%G", stmt);
>      }
> ...
>
> I'm working on a patch.
> >
> >> Kind Regards,
> >> Andre