[Bug middle-end/98088] [9/10/11 Regression] ICE in expand_oacc_collapse_init, at omp-expand.c:1533

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98088

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Hafiz Abid Qadeer <abidh@gcc.gnu.org>:

https://gcc.gnu.org/g:ac200799acb5cd2fb9e1758f6bf5fff1978daaeb

commit r11-8123-gac200799acb5cd2fb9e1758f6bf5fff1978daaeb
Author: Hafiz Abid Qadeer <abidh@codesourcery.com>
Date:   Thu Apr 8 17:31:30 2021 +0100

    [OpenACC] Fix an ICE where a loop with GT condition is collapsed.

    We have seen an ICE both on trunk and devel/omp/gcc-10 branches which can
    be reprodued with this simple testcase.  It occurs if an OpenACC loop has
    a collapse clause and any of the loop being collapsed uses GT or GE
    condition.  This issue is specific to OpenACC.

    int main (void)
    {
      int ix, iy;
      int dim_x = 16, dim_y = 16;
      {
           for (iy = dim_y - 1; iy > 0; --iy)
           for (ix = dim_x - 1; ix > 0; --ix)
            ;
      }
    }

    The problem is caused by a failing assertion in expand_oacc_collapse_init.
    It checks that cond_code for fd->loop should be same as cond_code for all
    the loops that are being collapsed.  As the cond_code for fd->loop is
    LT_EXPR with collapse clause (set at the end of omp_extract_for_data),
    this assertion forces that all the loop in collapse clause should use
    < operator.

    There does not seem to be anything in the code which demands this
    condition as loop with > condition works ok otherwise.  I digged old
    mailing list a bit but could not find any discussion on this change.
    Looking at the code, expand_oacc_for checks that fd->loop->cond_code is
    either LT_EXPR or GT_EXPR.  I guess the original intention was to have
    similar checks on the loop which are being collapsed. But the way check
    was written does not acheive that.

    I have fixed it by modifying the check in the assertion to be same as
    check on fd->loop->cond_code.

    I tested goacc and libgomp (with nvptx offloading) and did not see any
    regression.  I have added new tests to check collapse with GT/GE condition.

            PR middle-end/98088
            gcc/
            * omp-expand.c (expand_oacc_collapse_init): Update condition in
            a gcc_assert.

            gcc/testsuite/
            * c-c++-common/goacc/collapse-2.c: New.

            libgomp/
            * testsuite/libgomp.oacc-c-c++-common/collapse-2.c: Add check
            for loop with GT/GE condition.
            * testsuite/libgomp.oacc-c-c++-common/collapse-3.c: Likewise.