[Bug c++/112769] New: ICE on valid code related to requires-expression

[Bug c++/112769] New: ICE on valid code related to requires-expression

[janpmoeller at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112769

            Bug ID: 112769
           Summary: ICE on valid code related to requires-expression
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: janpmoeller at gmx dot de
  Target Milestone: ---

All gcc versions since (and including) 11.2 reject the following valid C++20
code:

//////////////////////////////////////////////////////////////
template<int I, typename T>
struct type
{
    constexpr explicit type(T value)
    {
    }

    template<typename U>
    constexpr explicit type(type<I, U> value)
        requires requires { T{value}; }
    {
    }
};

template <typename T>
using alias = type<0, T>;

constexpr alias foo{123};
//////////////////////////////////////////////////////////////


The reported error is:

##############################################################
<source>:11:18: internal compiler error: in add_outermost_template_args, at
cp/pt.cc:617
   11 |         requires requires { T{value}; }
      |                  ^~~~~~~~~~~~~~~~~~~~~~
0x1ce7bde internal_error(char const*, ...)
        ???:0
0x7290fc fancy_abort(char const*, int, char const*)
        ???:0
0x7879b6 tsubst_requires_expr(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x783c90 tsubst_constraint(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x783df1 tsubst_constraint_info(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x8b1e90 do_auto_deduction(tree_node*, tree_node*, tree_node*, int,
auto_deduction_context, tree_node*, int, tree_node*)
        ???:0
0x7ccd01 cp_finish_decl(tree_node*, tree_node*, bool, tree_node*, int)
        ???:0
0x89fd5b c_parse_file()
        ???:0
0x98c5d9 c_common_parse_file()
        ???:0
Please submit a full bug report, with preprocessed source.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
Preprocessed source stored into /tmp/cclpGAjI.out file, please attach this to
your bugreport.
Compiler returned: 1
##############################################################

gcc-11.1 accepts the code.Here is a link to compiler explorer with the same
example: https://godbolt.org/z/aq1d53anv

Note that the first (non-template) constructor is required to make the code
valid, but it is not required to reproduce the issue. Removing it still leads
to the same ICE on gcc > 11.1, whereas gcc-11.1 (correctly) rejects it due to
failed argument deduction.

[Bug c++/112769] ICE on valid code related to requires-expression

[janpmoeller at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112769

--- Comment #1 from janpmoeller at gmx dot de ---
The following equivalent program does not trigger the ICE:

//////////////////////////////////////////////////////////////
template<typename T, typename U>
concept C = requires (U u) { T{u}; };

template<int I, typename T>
struct type
{
    constexpr explicit type(T value)
    {
    }

    template<typename U>
    constexpr explicit type(type<I, U> value)
        requires C<T, type<I, U>>
    {
    }
};

template <typename T>
using alias = type<0, T>;

constexpr alias foo{123};
//////////////////////////////////////////////////////////////

[Bug c++/112769] [11/12/13/14 Regression] ICE on valid code related to requires-expression

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112769

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
                 CC|                            |ppalka at gcc dot gnu.org
            Summary|ICE on valid code related   |[11/12/13/14 Regression]
                   |to requires-expression      |ICE on valid code related
                   |                            |to requires-expression
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-02-02
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=101181
   Target Milestone|---                         |11.5
      Known to work|                            |11.1.0
      Known to fail|                            |11.4.0, 12.3.0, 13.2.0,
                   |                            |14.0

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Confirmed, we started ICEing with a non-checking compiler after r12-2222 /
r11-8734.

[Bug c++/112769] [11/12/13/14 Regression] ICE on valid code related to requires-expression

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112769

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|https://gcc.gnu.org/bugzill |
                   |a/show_bug.cgi?id=111222    |
                 CC|                            |stevenxia990430 at gmail dot com

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 111222 has been marked as a duplicate of this bug. ***

[Bug c++/112769] [11/12/13/14 Regression] ICE on valid code related to requires-expression

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112769

--- Comment #4 from GCC 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:686b5eb9c9ee623a604dde5c49fa11c23f384c62

commit r14-8770-g686b5eb9c9ee623a604dde5c49fa11c23f384c62
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Feb 2 19:07:08 2024 -0500

    c++: requires-exprs and partial constraint subst [PR110006]

    In r11-3261-gb28b621ac67bee we made tsubst_requires_expr never partially
    substitute into a requires-expression so as to avoid checking its
    requirements out of order during e.g. generic lambda regeneration.

    These PRs however illustrate that we still sometimes do need to
    partially substitute into a requires-expression, in particular when it
    appears in associated constraints that we're directly substituting for
    sake of declaration matching or dguide constraint rewriting.  In these
    cases we're being called from tsubst_constraint during which
    processing_constraint_expression_p is true, so this patch checks this
    predicate to control whether we defer substitution or partially
    substitute.

    In turn, we now need to propagate semantic tsubst flags through
    tsubst_requires_expr rather than just using tf_none, notably for sake of
    dguide constraint rewriting which sets tf_dguide.

            PR c++/110006
            PR c++/112769

    gcc/cp/ChangeLog:

            * constraint.cc (subst_info::quiet): Accomodate non-diagnostic
            tsubst flags.
            (tsubst_valid_expression_requirement): Likewise.
            (tsubst_simple_requirement): Return a substituted _REQ node when
            processing_template_decl.
            (tsubst_type_requirement_1): Accomodate non-diagnostic tsubst
            flags.
            (tsubst_type_requirement): Return a substituted _REQ node when
            processing_template_decl.
            (tsubst_compound_requirement): Likewise.  Accomodate non-diagnostic
            tsubst flags.
            (tsubst_nested_requirement): Likewise.
            (tsubst_requires_expr): Don't defer partial substitution when
            processing_constraint_expression_p is true, in which case return
            a substituted REQUIRES_EXPR.
            * pt.cc (tsubst_expr) <case REQUIRES_EXPR>: Accomodate
            non-diagnostic tsubst flags.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/class-deduction-alias18.C: New test.
            * g++.dg/cpp2a/concepts-friend16.C: New test.

    Reviewed-by: Jason Merrill <jason@redhat.com>

[Bug c++/112769] [11/12/13 Regression] ICE on valid code related to requires-expression

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112769

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[11/12/13/14 Regression]    |[11/12/13 Regression] ICE
                   |ICE on valid code related   |on valid code related to
                   |to requires-expression      |requires-expression

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 14 so far.

[Bug c++/112769] [11/12 Regression] ICE on valid code related to requires-expression

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112769

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[11/12/13 Regression] ICE   |[11/12 Regression] ICE on
                   |on valid code related to    |valid code related to
                   |requires-expression         |requires-expression

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Now also backported for GCC 13.3 as r13-8608-g38c2679ff9330d and
r13-8609-g265f207a46bc38.