[Patch, fortran] PR34640 - ICE when assigning item of a derived-component to a pointer

[Paul Richard Thomas <paul dot richard dot thomas at gmail dot com>]

Dear All,

Please find attached a draft patch for the above PR, together with PRs
40737, 55763, 57019 and 57116. These PRs constitute problems
associated with the last F95 feature that gfortran does not completely
implement.

I want to sound out if this is acceptable as the way to fix these
problems before going to the trouble of doing the final clean up;
especially of trans.c (gfc_build_array_ref) and
trans-array.c(build_array_ref).

The problem concerns pointers to derived type array components. eg:
pointer_array(:) => derived_array (:)%component

At present gfortran uses a rather crude fix, where a 'span' variable
with value of sizeof(element of derived_array) is used for pointer
arithmetic to access elements of the array;
&pointer_array(i) = &derived_array(1)%component + span*(i-1)

The difficulty of using a variable 'span' is that it is not passed to
procedures and it is not available to array pointer components. This
patch fixes this by the introduction of a span field in the array
descriptor. Note that this is only used for intrinsic type, pointer
arrays in this version of the patch. A considerable simplification
would arise from using the span field in class arrays too. This might
well be one result of the clean up mentioned above.

Tobias Burnus and I have been putting off fixing these PRs for a long
time because of the pending array descriptor reform. However, work on
fortran-dev has once again stopped and neither I nor, I think, anybody
else has the time to restart this work anytime soon.

pointer[1,2].f90 in the libgomp testsuite fail if this modification to
array referencing is exposed to them. For the time being,
trans-array.c(is_pointer_array) has:
+   if (flag_openmp)
+     return false;
to switch off the modification. I will come back to this during the
clean up, with the hope of putting it right.

Bootstraps and regtests on FC23/x86_64 - OK to proceed to completion
and submission?

Paul


2017-06-24  Paul Thomas  <pault@gcc.gnu.org>

    PR fortran/34640
    PR fortran/40737
    PR fortran/55763
    PR fortran/57019
    PR fortran/57116

    * trans-array.c: Add SPAN_FIELD and update indices for
    subsequent fields.
    (gfc_conv_descriptor_span, gfc_conv_descriptor_span_get,
    gfc_conv_descriptor_span_set, is_pointer_array,
    get_array_span): New functions.
    (gfc_conv_scalarized_array_ref): If the expression is a subref
    array, make sure that info->descriptor is a descriptor type.
    Otherwise, if info->descriptor is a pointer array, set 'decl'
    and fix it if it is a component reference.
    (gfc_conv_array_ref): Similarly set 'decl'.
    (gfc_array_allocate): Set the span field if this is a pointer
    array.
    (gfc_conv_expr_descriptor): Set the span field for pointer
    assignments.
    * trans-array.h: Prototypes for gfc_conv_descriptor_span_get
    and gfc_conv_descriptor_span_set added.
    * trans.c (gfc_build_array_ref): GFC_DECL_SUBREF_ARRAY_P change
    to GFC_DECL_PTR_ARRAY_P and defreference if a PARM_DECL.
    trans-decl.c (gfc_get_symbol_decl): If a non-class pointer
    array, mark the declaration as a GFC_DECL_PTR_ARRAY_P. Remove
    the setting of GFC_DECL_SPAN.
    (gfc_trans_deferred_vars): Set the span field to zero in the
    originating scope.
    * trans-expr.c (gfc_trans_pointer_assignment): Remove code for
    setting of GFC_DECL_SPAN. Set the 'span' field for non-class
    pointers to class function results. Likewise for rank remap.
    * trans.h : Rename DECL_LANG_FLAG_6, GFC_DECL_SUBREF_ARRAY_P,
    as GFC_DECL_PTR_ARRAY_P.
    * trans-intrinsic.c (conv_expr_ref_to_caf_ref): Pick up the
    'token' offset from the field decl in the descriptor.
    (conv_isocbinding_subroutine): Set the 'span' field.
    * trans-io.c (gfc_trans_transfer): Always scalarize pointer
    array io.
    * trans-stmt.c (trans_associate_var): Set the 'span' field.
    * trans-types.c (gfc_get_array_descriptor_base): Add the 'span'
    field to the array descriptor.
    (gfc_get_derived_type): Pointer array components are marked as
    GFC_DECL_PTR_ARRAY_P.
    (gfc_get_array_descr_info): Jump one more in the DECL_CHAIN to
    access the offset field.


2017-06-24  Paul Thomas  <pault@gcc.gnu.org>

    PR fortran/34640
    * gfortran.dg/assumed_type_2.f90: Adjust some of the tree dump
    checks.
    * gfortran.dg/no_arg_check_2.f90: Likewise.
    * gfortran.dg/pointer_array_1.f90: New test.
    * gfortran.dg/pointer_array_2.f90: New test.
    * gfortran.dg/pointer_array_component_1.f90: New test.
    * gfortran.dg/pointer_array_component_2.f90: New test.
    * gfortran.dg/goacc/kernels-alias-4.f95: Bump up both tree scan
    counts by 1.

    PR fortran/40737
    * gfortran.dg/pointer_array_3.f90: New test.

    PR fortran/57116
    * gfortran.dg/pointer_array_4.f90: New test.

    PR fortran/55763
    * gfortran.dg/pointer_array_5.f90: New test.

    PR fortran/57019
    * gfortran.dg/pointer_array_6.f90: New test.

2017-06-24  Paul Thomas  <pault@gcc.gnu.org>

    PR fortran/34640
    * libgfortran/libgfortran.h: Add span field to descriptor.


-- 
"If you can't explain it simply, you don't understand it well enough"
- Albert Einstein

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