The description of CFI_cdesc_t in section 18.5.3 of the 2018 Fortran standard includes this constraint: There shall be an ordering of the dimensions such that the absolute value of the sm member of the first dimension is not less than the elem_len member of the C descriptor and the absolute value of the sm member of each subsequent dimension is not less than the absolute value of the sm member of the previous dimension multiplied by the extent of the previous dimension. In the WIP TS 29113 testsuite posted here https://gcc.gnu.org/pipermail/gcc-patches/2021-July/574115.html the testcase interoperability/fc-descriptor-7.f90 passes the result of the TRANSPOSE intrinsic to a C function with an assumed-shape array argument, and the descriptor it receives does not satisfy this constraint. It dumps as <CFI_cdesc_t base_addr=0x7ffcb2e98a40 elem_len=4 version=1 rank=2 type=CFI_type_int attribute=CFI_attribute_other dim=[<CFI_dim_t lower_bound=0 extent=5 sm=40>, <CFI_dim_t lower_bound=0 extent=10 sm=4>]>
BTW, I did not test any other intrinsics that rearrange the elements of their input array arguments. TRANPOSE seemed like the most obvious one to try first.
The master branch has been updated by Tobias Burnus <burnus@gcc.gnu.org>: https://gcc.gnu.org/g:64f9623765da3306b0ab6a47997dc5d62c2ea261 commit r12-4467-g64f9623765da3306b0ab6a47997dc5d62c2ea261 Author: Tobias Burnus <tobias@codesourcery.com> Date: Mon Oct 18 09:51:36 2021 +0200 Fortran: Fix Bind(C) Array-Descriptor Conversion gfortran uses internally a different array descriptor ("gfc") as Fortran 2018 alias TS291113 defines for C interoperability via ISO_Fortran_binding.h ("CFI"). Hence, when calling a C function from Fortran, it has to be converted in the callee - and if a BIND(C) procedure is written in Fortran, the CFI argument has to be converted to gfc in order work with the rest of the FE code and the library calls. Before this patch, part was handled in the FE generated code and other parts in libgfortran. With this patch, all code is generated and CFI is defined as proper type - visible in the debugger and to the middle end - avoiding both alias issues and missed optimization issues. This patch also fixes issues like: intent(out) deallocation in the bind(C) callee, using the CFI descriptor also for allocatable and pointer scalars and for len=* character strings. For 'select rank', it also optimizes the code + avoid accessing uninitialized memory if the dummy argument is allocatable/a pointer. It additionally rejects passing a descriptorless type(*) to an assumed-rank dummy argument. [F2018:C711] PR fortran/102086 PR fortran/92189 PR fortran/92621 PR fortran/101308 PR fortran/101309 PR fortran/101635 PR fortran/92482 gcc/fortran/ChangeLog: * decl.c (gfc_verify_c_interop_param): Remove 'sorry' for scalar allocatable/pointer and len=*. * expr.c (is_CFI_desc): Return true for for those. * gfortran.h (CFI_type_kind_shift, CFI_type_mask, CFI_type_from_type_kind, CFI_VERSION, CFI_MAX_RANK, CFI_attribute_pointer, CFI_attribute_allocatable, CFI_attribute_other, CFI_type_Integer, CFI_type_Logical, CFI_type_Real, CFI_type_Complex, CFI_type_Character, CFI_type_ucs4_char, CFI_type_struct, CFI_type_cptr, CFI_type_cfunptr, CFI_type_other): New #define. * trans-array.c (CFI_FIELD_BASE_ADDR, CFI_FIELD_ELEM_LEN, CFI_FIELD_VERSION, CFI_FIELD_RANK, CFI_FIELD_ATTRIBUTE, CFI_FIELD_TYPE, CFI_FIELD_DIM, CFI_DIM_FIELD_LOWER_BOUND, CFI_DIM_FIELD_EXTENT, CFI_DIM_FIELD_SM, gfc_get_cfi_descriptor_field, gfc_get_cfi_desc_base_addr, gfc_get_cfi_desc_elem_len, gfc_get_cfi_desc_version, gfc_get_cfi_desc_rank, gfc_get_cfi_desc_type, gfc_get_cfi_desc_attribute, gfc_get_cfi_dim_item, gfc_get_cfi_dim_lbound, gfc_get_cfi_dim_extent, gfc_get_cfi_dim_sm): New define/functions to access the CFI array descriptor. (gfc_conv_descriptor_type): New function for the GFC descriptor. (gfc_get_array_span): Handle expr of CFI descriptors and assumed-type descriptors. (gfc_trans_array_bounds): Remove 'static'. (gfc_conv_expr_descriptor): For assumed type, use the dtype of the actual argument. (structure_alloc_comps): Remove ' ' inside tabs. * trans-array.h (gfc_trans_array_bounds, gfc_conv_descriptor_type, gfc_get_cfi_desc_base_addr, gfc_get_cfi_desc_elem_len, gfc_get_cfi_desc_version, gfc_get_cfi_desc_rank, gfc_get_cfi_desc_type, gfc_get_cfi_desc_attribute, gfc_get_cfi_dim_lbound, gfc_get_cfi_dim_extent, gfc_get_cfi_dim_sm): New prototypes. * trans-decl.c (gfor_fndecl_cfi_to_gfc, gfor_fndecl_gfc_to_cfi): Remove global vars. (gfc_build_builtin_function_decls): Remove their initialization. (gfc_get_symbol_decl, create_function_arglist, gfc_trans_deferred_vars): Update for CFI. (convert_CFI_desc): Remove and replace by ... (gfc_conv_cfi_to_gfc): ... this function (gfc_generate_function_code): Call it; create local GFC var for CFI. * trans-expr.c (gfc_maybe_dereference_var): Handle CFI. (gfc_conv_subref_array_arg): Handle the if-noncontigous-only copy in when the result should be a descriptor. (gfc_conv_gfc_desc_to_cfi_desc): Completely rewritten. (gfc_conv_procedure_call): CFI fixes. * trans-openmp.c (gfc_omp_is_optional_argument, gfc_omp_check_optional_argument): Handle optional CFI. * trans-stmt.c (gfc_trans_select_rank_cases): Cleanup, avoid invalid code for allocatable/pointer dummies, which cannot be assumed size. * trans-types.c (gfc_cfi_descriptor_base): New global var. (gfc_get_dtype_rank_type): Skip rank init for rank < 0. (gfc_sym_type): Handle CFI dummies. (gfc_get_function_type): Update call. (gfc_get_cfi_dim_type, gfc_get_cfi_type): New. * trans-types.h (gfc_sym_type): Update prototype. (gfc_get_cfi_type): New prototype. * trans.c (gfc_trans_runtime_check): Make conditions more consistent to avoid '<logical> AND_THEN <long int>' in conditions. * trans.h (gfor_fndecl_cfi_to_gfc, gfor_fndecl_gfc_to_cfi): Remove global-var declaration. libgfortran/ChangeLog: * ISO_Fortran_binding.h (CFI_type_cfunptr): Make unique type again. * runtime/ISO_Fortran_binding.c (cfi_desc_to_gfc_desc, gfc_desc_to_cfi_desc): Add comment that those are no longer called by new code. libgomp/ChangeLog: * testsuite/libgomp.fortran/optional-bind-c.f90: New test. gcc/testsuite/ChangeLog: * gfortran.dg/ISO_Fortran_binding_4.f90: Extend testcase. * gfortran.dg/PR100914.f90: Remove xfail. * gfortran.dg/PR100915.c: Expect CFI_type_cfunptr. * gfortran.dg/PR100915.f90: Handle CFI_type_cfunptr != CFI_type_cptr. * gfortran.dg/PR93963.f90: Extend select-rank tests. * gfortran.dg/bind-c-intent-out.f90: Change to dg-do run, update scan-dump. * gfortran.dg/bind_c_array_params_2.f90: Update/extend scan-dump. * gfortran.dg/bind_c_char_10.f90: Update scan-dump. * gfortran.dg/bind_c_char_8.f90: Remove dg-error "sorry". * gfortran.dg/c-interop/allocatable-dummy.f90: Remove xfail. * gfortran.dg/c-interop/c1255-1.f90: Likewise. * gfortran.dg/c-interop/c407c-1.f90: Update dg-error. * gfortran.dg/c-interop/cf-descriptor-5.f90: Remove xfail. * gfortran.dg/c-interop/cf-out-descriptor-3.f90: Likewise. * gfortran.dg/c-interop/cf-out-descriptor-4.f90: Likewise. * gfortran.dg/c-interop/cf-out-descriptor-5.f90: Likewise. * gfortran.dg/c-interop/contiguous-2.f90: Likewise. * gfortran.dg/c-interop/contiguous-3.f90: Likewise. * gfortran.dg/c-interop/deferred-character-1.f90: Likewise. * gfortran.dg/c-interop/deferred-character-2.f90: Likewise. * gfortran.dg/c-interop/fc-descriptor-3.f90: Likewise. * gfortran.dg/c-interop/fc-descriptor-5.f90: Likewise. * gfortran.dg/c-interop/fc-descriptor-6.f90: Likewise. * gfortran.dg/c-interop/fc-out-descriptor-3.f90: Likewise. * gfortran.dg/c-interop/fc-out-descriptor-4.f90: Likewise. * gfortran.dg/c-interop/fc-out-descriptor-5.f90: Likewise. * gfortran.dg/c-interop/fc-out-descriptor-6.f90: Likewise. * gfortran.dg/c-interop/ff-descriptor-5.f90: Likewise. * gfortran.dg/c-interop/ff-descriptor-6.f90: Likewise. * gfortran.dg/c-interop/fc-descriptor-7.f90: Remove xfail + extend. * gfortran.dg/c-interop/fc-descriptor-7-c.c: Update for changes. * gfortran.dg/c-interop/shape.f90: Add implicit none. * gfortran.dg/c-interop/typecodes-array-char-c.c: Add kind=4 char. * gfortran.dg/c-interop/typecodes-array-char.f90: Likewise. * gfortran.dg/c-interop/typecodes-array-float128.f90: Remove xfail. * gfortran.dg/c-interop/typecodes-scalar-basic.f90: Likewise. * gfortran.dg/c-interop/typecodes-scalar-float128.f90: Likewise. * gfortran.dg/c-interop/typecodes-scalar-int128.f90: Likewise. * gfortran.dg/c-interop/typecodes-scalar-longdouble.f90: Likewise. * gfortran.dg/iso_c_binding_char_1.f90: Remove dg-error "sorry". * gfortran.dg/pr93792.f90: Turn XFAIL into PASS. * gfortran.dg/ISO_Fortran_binding_19.f90: New test. * gfortran.dg/assumed_type_12.f90: New test. * gfortran.dg/assumed_type_13.c: New test. * gfortran.dg/assumed_type_13.f90: New test. * gfortran.dg/bind-c-char-descr.f90: New test. * gfortran.dg/bind-c-contiguous-1.c: New test. * gfortran.dg/bind-c-contiguous-1.f90: New test. * gfortran.dg/bind-c-contiguous-2.f90: New test. * gfortran.dg/bind-c-contiguous-3.c: New test. * gfortran.dg/bind-c-contiguous-3.f90: New test. * gfortran.dg/bind-c-contiguous-4.c: New test. * gfortran.dg/bind-c-contiguous-4.f90: New test. * gfortran.dg/bind-c-contiguous-5.c: New test. * gfortran.dg/bind-c-contiguous-5.f90: New test.
FIXED (in GCC 12) Note: TRANSPOSE now yields an descriptor where the dimension are swapped, i.e. dim[0].sm > dim[1].sm, unless the dummy argument has to be contiguous. Otherwise, the testsuite passes now. (For SHAPE and polymorphism with RESHAPE and nested TRANSPOSE, other PRs exists.)