[Bug c++/101886] New: [11/12 Regression][concepts] ICE with auto as template parameter

[Bug c++/101886] New: [11/12 Regression][concepts] ICE with auto as template parameter

[reichelt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101886

            Bug ID: 101886
           Summary: [11/12 Regression][concepts] ICE with auto as template
                    parameter
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: reichelt at gcc dot gnu.org
  Target Milestone: ---

The following valid code snippet (compiled with "-fconcepts")
triggers an ICE since GCC 11.1.0:

========================================
template<typename...> struct A { };

A<int, int> a;
A<auto, auto> b1 = a;
A<auto, auto> b2 = a;
========================================

bug.cc:5:13: internal compiler error: same canonical type node for different
types 'auto' and 'auto'
    5 | A<auto, auto> b2 = a;
      |             ^
0xb4eb9d comptypes(tree_node*, tree_node*, int)
        ../../gcc-11.1.0/gcc/cp/typeck.c:1565
0xab322f template_args_equal(tree_node*, tree_node*, bool)
        ../../gcc-11.1.0/gcc/cp/pt.c:9231
0xb42e41 cp_tree_equal(tree_node*, tree_node*)
        ../../gcc-11.1.0/gcc/cp/tree.c:4079
0xab305a template_args_equal(tree_node*, tree_node*, bool)
        ../../gcc-11.1.0/gcc/cp/pt.c:9249
0xab2d88 template_args_equal(tree_node*, tree_node*, bool)
        ../../gcc-11.1.0/gcc/cp/pt.c:9194
0xab2d88 comp_template_args(tree_node*, tree_node*, tree_node**, tree_node**,
bool)
        ../../gcc-11.1.0/gcc/cp/pt.c:9278
0xab2d88 comp_template_args(tree_node*, tree_node*, tree_node**, tree_node**,
bool)
        ../../gcc-11.1.0/gcc/cp/pt.c:9258
0xabc9f3 spec_hasher::equal(spec_entry*, spec_entry*)
        ../../gcc-11.1.0/gcc/cp/pt.c:1727
0xb02944 hash_table<spec_hasher, false,
xcallocator>::find_with_hash(spec_entry* const&, unsigned int)
        ../../gcc-11.1.0/gcc/hash-table.h:923
0xaeef47 lookup_template_class_1
        ../../gcc-11.1.0/gcc/cp/pt.c:9889
0xaf0bfc lookup_template_class(tree_node*, tree_node*, tree_node*, tree_node*,
int, int)
        ../../gcc-11.1.0/gcc/cp/pt.c:10244
0xb1914b finish_template_type(tree_node*, tree_node*, int)
        ../../gcc-11.1.0/gcc/cp/semantics.c:3581
0xa8a8eb cp_parser_template_id
        ../../gcc-11.1.0/gcc/cp/parser.c:17486
0xa8aadb cp_parser_class_name
        ../../gcc-11.1.0/gcc/cp/parser.c:24722
0xa81fda cp_parser_qualifying_entity
        ../../gcc-11.1.0/gcc/cp/parser.c:7002
0xa81fda cp_parser_nested_name_specifier_opt
        ../../gcc-11.1.0/gcc/cp/parser.c:6684
0xaa2e18 cp_parser_template_introduction
        ../../gcc-11.1.0/gcc/cp/parser.c:30254
0xaa50c3 cp_parser_declaration
        ../../gcc-11.1.0/gcc/cp/parser.c:14149
0xaa5e4c cp_parser_toplevel_declaration
        ../../gcc-11.1.0/gcc/cp/parser.c:14183
0xaa5e4c cp_parser_translation_unit
        ../../gcc-11.1.0/gcc/cp/parser.c:4942
Please submit a full bug report, [etc.]

[Bug c++/101886] [11/12 Regression][concepts] ICE with auto as template parameter

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101886

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.3

[Bug c++/101886] [11/12 Regression][concepts] ICE with auto as template parameter since r11-7011-g6e0a231a4aa2407b

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101886

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
            Summary|[11/12                      |[11/12
                   |Regression][concepts] ICE   |Regression][concepts] ICE
                   |with auto as template       |with auto as template
                   |parameter                   |parameter since
                   |                            |r11-7011-g6e0a231a4aa2407b
   Last reconfirmed|                            |2021-08-13
     Ever confirmed|0                           |1
                 CC|                            |jason at gcc dot gnu.org,
                   |                            |marxin at gcc dot gnu.org

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Started with r11-7011-g6e0a231a4aa2407b.

[Bug c++/101886] [11/12 Regression][concepts] ICE with auto as template parameter since r11-7011-g6e0a231a4aa2407b

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101886

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug c++/101886] [11/12 Regression][concepts] ICE with auto as template argument since r11-7011-g6e0a231a4aa2407b

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101886

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
This use of 'auto' was not accepted into C++20, so fixing this bug in the
vestigial Concepts TS implementation is a low priority.

[Bug c++/101886] [11/12 Regression][concepts TS] ICE with auto as template argument since r11-7011-g6e0a231a4aa2407b

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101886

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.3                        |11.4

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 11.3 is being released, retargeting bugs to GCC 11.4.

[Bug c++/101886] [11/12/13 Regression][concepts TS] ICE with auto as template argument since r11-7011-g6e0a231a4aa2407b

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101886

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:a7c8036b26082d8da001e05596777c5f911590e1

commit r13-4799-ga7c8036b26082d8da001e05596777c5f911590e1
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Dec 19 14:59:43 2022 -0500

    c++: ICE with concepts TS multiple auto deduction [PR101886]

    In extract_autos_r, we need to recompute TYPE_CANONICAL for the template
    type parameter after adjusting its index, otherwise we end up with a
    comptypes ICE for the below testcase.  Note that such in-place type
    adjustment isn't generally safe to do since the type could be the
    TYPE_CANONICAL of another (unadjusted) type, but in this case the
    canonical auto (of some level and 0 index) is the first auto (of that
    level) that's created, and so any auto that we do end up adjusting can't
    be the canonical one.

            PR c++/101886

    gcc/cp/ChangeLog:

            * pt.cc (extract_autos_r): Recompute TYPE_CANONICAL after
            adjusting the template type parameter's index.  Simplify
            by using TEMPLATE_TYPE_IDX.  Add some sanity checks.

    gcc/testsuite/ChangeLog:

            * g++.dg/concepts/auto5.C: New test.

[Bug c++/101886] [11/12 Regression][concepts TS] ICE with auto as template argument since r11-7011-g6e0a231a4aa2407b

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101886

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
            Summary|[11/12/13                   |[11/12 Regression][concepts
                   |Regression][concepts TS]    |TS] ICE with auto as
                   |ICE with auto as template   |template argument since
                   |argument since              |r11-7011-g6e0a231a4aa2407b
                   |r11-7011-g6e0a231a4aa2407b  |
                 CC|                            |ppalka at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

[Bug c++/101886] [11/12 Regression][concepts TS] ICE with auto as template argument since r11-7011-g6e0a231a4aa2407b

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101886

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:8aa045c97485d75e0b6eb1068464c0ddaa6beacb

commit r13-4810-g8aa045c97485d75e0b6eb1068464c0ddaa6beacb
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Dec 20 17:02:37 2022 -0500

    c++, tree: walk TREE_VEC (and VECTOR_CST) in natural order [PR101886]

    Unfortunately the extract_autos_r fix in r13-4799-ga7c8036b26082d is
    derailed by the fact that walk_tree_1 currently walks the elements of a
    TREE_VEC in reverse, which means for A<auto, auto> in the below testcase
    extract_autos_r ends up adjusting the TEMPLATE_TYPE_IDX of the first
    auto instead of the second one, and the first auto is the canonical auto
    of level 2 (and index 0), so we rightfully trigger the sanity check
    added in that commit.

    It seems TREE_VEC and VECTOR_CST are the only trees we walk in reverse,
    and this has been the case since r21884 whence the original version of
    walk_tree_1 was introduced.  But that's arguably unnatural and not
    consistent with how we walk all other compound trees such as CONSTRUCTORs
    and EXPR_P trees in forward order.

    So this patch makes walk_tree_1 walk TREE_VEC (and VECTOR_CST) in
    forward order as well, which fixes the testcase.  Doing so revealed that
    keep_template_parm grows the list of found template parameters from the
    front, which previously compensated for the TREE_VEC behavior, so now we
    should grow it from the back.

            PR c++/101886

    gcc/cp/ChangeLog:

            * pt.cc (find_template_parameter_info::parm_list_tail):
            New data member.
            (keep_template_parm): Use parm_list_tail to append rather
            than prepend to parm_list.

    gcc/ChangeLog:

            * tree.cc (walk_tree_1) <case TREE_VEC>: Walk the elements
            in forward instead of reverse order.
            <case VECTOR_CST>: Likewise.

    gcc/testsuite/ChangeLog:

            * g++.dg/concepts/diagnostic12.C: Adjust expected order of
            template parameters within pretty printed parameter mapping.
            * g++.dg/concepts/auto6.C: New test.

[Bug c++/101886] [11/12 Regression][concepts TS] ICE with auto as template argument since r11-7011-g6e0a231a4aa2407b

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101886

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
   Target Milestone|11.4                        |13.0
             Status|ASSIGNED                    |RESOLVED

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 13, this doesn't seem worth backporting since the bug is Concepts
TS specific.