[Bug target/100232] [OpenMP][nvptx] Reduction fails with optimization and 'loop'/'for simd' but not with 'for'

[cvs-commit at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100232

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Tom de Vries
<vr...@gcc.gnu.org>:

https://gcc.gnu.org/g:f94c6caac7f03815c26c03a532f834c37517519c

commit r11-8324-gf94c6caac7f03815c26c03a532f834c37517519c
Author: Tom de Vries <tdevr...@suse.de>
Date:   Wed Apr 28 16:00:01 2021 +0200

    [omp, simt] Fix expand_GOMP_SIMT_*

    When running the test-case included in this patch using an
    nvptx accelerator, it fails in execution.

    The problem is that the expansion of GOMP_SIMT_XCHG_BFLY is optimized away
    during pass_jump as "trivially dead insns".

    This is caused by this code in expand_GOMP_SIMT_XCHG_BFLY:
    ...
      class expand_operand ops[3];
      create_output_operand (&ops[0], target, mode);
      ...
      expand_insn (targetm.code_for_omp_simt_xchg_bfly, 3, ops);
    ...
    which doesn't guarantee that target is assigned to by the expanded insn.

    F.i., if target is:
    ...
    (gdb) call debug_rtx ( target )
    (subreg/s/u:QI (reg:SI 40 [ _61 ]) 0)
    ...
    then after expand_insn, we have:
    ...
    (gdb) call debug_rtx ( ops[0].value )
    (reg:QI 57)
    ...

    See commit 3af3bec2e4d "internal-fn: Avoid dropping the lhs of some
    calls [PR94941]" for a similar problem.

    Fix this in the same way, by adding:
    ...
      if (!rtx_equal_p (target, ops[0].value))
        emit_move_insn (target, ops[0].value);
    ...
    where applicable in the expand_GOMP_SIMT_* functions.

    Tested libgomp on x86_64 with nvptx accelerator.

    gcc/ChangeLog:

    2021-04-28  Tom de Vries  <tdevr...@suse.de>

            PR target/100232
            * internal-fn.c (expand_GOMP_SIMT_ENTER_ALLOC)
            (expand_GOMP_SIMT_LAST_LANE, expand_GOMP_SIMT_ORDERED_PRED)
            (expand_GOMP_SIMT_VOTE_ANY, expand_GOMP_SIMT_XCHG_BFLY)
            (expand_GOMP_SIMT_XCHG_IDX): Ensure target is assigned to.

    (cherry picked from commit 4d7c874e2c64ebf7631049ace642d246843febae)