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Subject: [Bug target/100321] [OpenMP][nvptx, SIMT] (Con't) Reduction fails
 with optimization and 'loop'/'for simd' but not with 'for'
Date: Mon, 03 May 2021 21:14:21 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100321

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom de Vries <vries@gcc.gnu.org>:

https://gcc.gnu.org/g:f87990a2a8fc9e20d30462a0a4c9047582af0cd9

commit r12-395-gf87990a2a8fc9e20d30462a0a4c9047582af0cd9
Author: Tom de Vries <tdevries@suse.de>
Date:   Mon May 3 11:36:14 2021 +0200

    [openmp, simt] Disable SIMT for user-defined reduction

    The test-case included in this patch contains this target region:
    ...
      for (int i0 =3D 0 ; i0 < N0 ; i0++ )
        counter_N0.i +=3D 1;
    ...

    When running with nvptx accelerator, the counter variable is expected to
    be N0 after the region, but instead is N0 / 32.  The problem is that ra=
ther
    than getting the result for all warp lanes, we get it for just one lane.

    This is caused by the implementation of SIMT being incomplete.  It hand=
les
    regular reductions, but appearantly not user-defined reductions.

    For now, handle this by disabling SIMT in this case, specifically by
setting
    sctx->max_vf to 1.

    Tested libgomp on x86_64-linux with nvptx accelerator.

    gcc/ChangeLog:

    2021-05-03  Tom de Vries  <tdevries@suse.de>

            PR target/100321
            * omp-low.c (lower_rec_input_clauses): Disable SIMT for
user-defined
            reduction.

    libgomp/ChangeLog:

    2021-05-03  Tom de Vries  <tdevries@suse.de>

            PR target/100321
            * testsuite/libgomp.c/target-44.c: New test.=