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 <mik...@gcc.gnu.org>: https://gcc.gnu.org/g:7964ab6c364c410c34efe7ca2eba797d36525349 commit r12-8230-g7964ab6c364c410c34efe7ca2eba797d36525349 Author: Mikael Morin <mik...@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 <rguent...@suse.de>
