[Bug target/104456] New: nvptx: prevent_branch_around_nothing doesn't handle asm ("")

[Bug target/104456] New: nvptx: prevent_branch_around_nothing doesn't handle asm ("")

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104456

            Bug ID: 104456
           Summary: nvptx: prevent_branch_around_nothing doesn't handle
                    asm ("")
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

Testing on a GT 1030, with driver 510.x, GOMP_NVPTX_JIT=-00 and -mptx=3.1, I
run into:
...
FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/acc_prof-version-1.c
-DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O2 
execution test
...

The test-case runs into the warp divergence check, because we have:
...
@ %r23 bra $L2;
$L2:
...

The prevent_branch_around_nothing is supposed to handle this, but it doesn't
trigger for 'asm ("")'.

[Bug target/104456] nvptx: prevent_branch_around_nothing doesn't handle asm ("")

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104456

--- Comment #1 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:fd64b09217fbe8fa33b559e61564071e8aca71e5

commit r12-7190-gfd64b09217fbe8fa33b559e61564071e8aca71e5
Author: Tom de Vries <tdevries@suse.de>
Date:   Thu Feb 10 11:26:16 2022 +0100

    [nvptx] Handle asm insn in prevent_branch_around_nothing

    With GOMP_NVPTX_JIT=-00 and -mptx=3.1, I run into:
    ...
    FAIL: libgomp.oacc-c/../libgomp.oacc-c-c++-common/acc_prof-version-1.c \
      -DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O2 \
      execution test
    ...

    The problem is that we're generating a diverging branch around nothing:
    ...
            {
                    .reg.u32        %x;
                    mov.u32 %x, %tid.x;
                    setp.ne.u32     %r23, %x, 0;
            }
            @%r23   bra     $L2;
    $L2:
    ...
    which the driver JIT has problems with at -O0, so consequently we run into
the
    nvptx_uniform_warp_check.

    Fix this by handling asm ("") and alike in prevent_branch_around_nothing.

    Tested on x86_64 with nvptx accelerator.

    gcc/ChangeLog:

    2022-02-10  Tom de Vries  <tdevries@suse.de>

            PR target/104456
            * config/nvptx/nvptx.cc (prevent_branch_around_nothing): Handle asm
            insn.

[Bug target/104456] nvptx: prevent_branch_around_nothing doesn't handle asm ("")

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104456

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.0
         Resolution|---                         |FIXED
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Tom de Vries <vries at gcc dot gnu.org> ---
Fixed by "[nvptx] Handle asm insn in prevent_branch_around_nothing".