[Bug fortran/102043] [9/10/11/12 Regression] Wrong array types used for negative stride accesses, gfortran.dg/vector_subscript_1.f90 FAILs

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102043

--- Comment #47 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Mikael Morin <mikael@gcc.gnu.org>:

https://gcc.gnu.org/g:7964ab6c364c410c34efe7ca2eba797d36525349

commit r12-8230-g7964ab6c364c410c34efe7ca2eba797d36525349
Author: Mikael Morin <mikael@gcc.gnu.org>
Date:   Fri Apr 22 22:52:50 2022 +0200

    fortran: Use pointer arithmetic to index arrays [PR102043]

    The code generated for array references used to be ARRAY_REF trees as
    could be expected.  However, the middle-end may conclude from those
    trees that the indexes used are non-negative (more precisely not below
    the lower bound), which is a wrong assumption in the case of "reversed-
    order" arrays.

    The problematic arrays are those with a descriptor and having a negative
    stride for at least one dimension.  The descriptor data points to the
    first element in array order (which is not the first in memory order in
    that case), and the negative stride(s) makes walking the array backwards
    (towards lower memory addresses), and we can access elements with
    negative index wrt data pointer.

    With this change, pointer arithmetic is generated by default for array
    references, unless we are in a case where negative indexes canât happen
    (array descriptorâs dim element, substrings, explicit shape,
    allocatable, or assumed shape contiguous).  A new flag is added to
    choose between array indexing and pointer arithmetic, and itâs set
    if the context can tell array indexing is safe (descriptor dim
    element, substring, temporary array), or a new method is called
    to decide on whether the flag should be set for one given array
    expression.

            PR fortran/102043

    gcc/fortran/ChangeLog:

            * trans.h (gfc_build_array_ref): Add non_negative_offset
            argument.
            * trans.cc (gfc_build_array_ref): Ditto. Use pointer arithmetic
            if non_negative_offset is false.
            * trans-expr.cc (gfc_conv_substring): Set flag in the call to
            gfc_build_array_ref.
            * trans-array.cc (gfc_get_cfi_dim_item,
            gfc_conv_descriptor_dimension): Same.
            (build_array_ref): Decide on whether to set the flag and update
            the call.
            (gfc_conv_scalarized_array_ref): Same.  New argument tmp_array.
            (gfc_conv_tmp_array_ref): Update call to
            gfc_conv_scalarized_ref.
            (non_negative_strides_array_p): New function.

    gcc/testsuite/ChangeLog:

            * gfortran.dg/array_reference_3.f90: New.
            * gfortran.dg/negative_stride_1.f90: New.
            * gfortran.dg/vector_subscript_8.f90: New.
            * gfortran.dg/vector_subscript_9.f90: New.
            * gfortran.dg/c_loc_test_22.f90: Update dump patterns.
            * gfortran.dg/finalize_10.f90: Same.

    Co-Authored-By: Richard Biener <rguenther@suse.de>