[Bug c++/99874] New: ICE Segmentation fault when declared variable template of template lambda

[Bug c++/99874] New: ICE Segmentation fault when declared variable template of template lambda

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99874

            Bug ID: 99874
           Summary: ICE Segmentation fault when declared variable template
                    of template lambda
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

https://godbolt.org/z/4fxhP6jf9

template <int>
auto l = []<int x> requires requires { x; } {};

int main() {
  l<0>.template operator()<0>();
}


<source>:2:40: internal compiler error: Segmentation fault
    2 | auto l = []<int x> requires requires { x; } {};
      |                                        ^
0x1cfca39 internal_error(char const*, ...)
        ???:0
0x917a92 tsubst(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x73f042 tsubst_requires_expr(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x73f08a constraints_satisfied_p(tree_node*, tree_node*)
        ???:0
0x954d48 fn_type_unification(tree_node*, tree_node*, tree_node*, tree_node*
const*, unsigned int, tree_node*, unification_kind_t, int, conversion**, bool,
bool)
        ???:0
0x6ded59 build_new_method_call(tree_node*, tree_node*, vec<tree_node*, va_gc,
vl_embed>**, tree_node*, int, tree_node**, int)
        ???:0
0x8e126d c_parse_file()
        ???:0
0xa60292 c_common_parse_file()
        ???:0
Please submit a full bug report,
with preprocessed source if appropriate.

[Bug c++/99874] [11 Regression] ICE Segmentation fault when declared variable template of template lambda

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99874

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.0
           Priority|P3                          |P1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-04-01
                 CC|                            |mpolacek at gcc dot gnu.org,
                   |                            |ppalka at gcc dot gnu.org
     Ever confirmed|0                           |1
            Summary|ICE Segmentation fault when |[11 Regression] ICE
                   |declared variable template  |Segmentation fault when
                   |of template lambda          |declared variable template
                   |                            |of template lambda

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Confirmed.  G++10:

99874.C:2:45: error: expected ‘(’ before ‘{’ token
    2 | auto l = []<int x> requires requires { x; } {};
      |                                             ^
      |                                             (

ICE started with r11-3261.  I suppose it's a P1 then?

[Bug c++/99874] [11 Regression] ICE Segmentation fault when declared variable template of template lambda

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99874

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #1)
> Confirmed.  G++10:
> 
> 99874.C:2:45: error: expected ‘(’ before ‘{’ token
>     2 | auto l = []<int x> requires requires { x; } {};
>       |                                             ^
>       |                                             (
> 
> ICE started with r11-3261.  I suppose it's a P1 then?

Probably -- if we add an empty parameter list to the lambda then G++10 accepts.
 Looking into it.

[Bug c++/99874] [11 Regression] ICE Segmentation fault when declared variable template of template lambda

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99874

--- Comment #3 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:123b3e03c911a43054c1f88f5d3110e1d084dd4e

commit r11-8065-g123b3e03c911a43054c1f88f5d3110e1d084dd4e
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Apr 8 13:07:43 2021 -0400

    c++: Don't substitute into constraints on lambdas [PR99874]

    We currently substitute through a lambda's constraints whenever we
    regenerate it via tsubst_lambda_expr.  This is the wrong approach
    because it can lead to hard errors due to constraints being evaluated
    out of order (as in the testcase concepts-lambda17.C below), and because
    it doesn't mesh well with the recently added REQUIRES_EXPR_EXTRA_ARGS
    mechanism for delaying substitution into requires-expressions, which is
    the cause of this PR.

    But in order to avoid substituting through a lambda's constraints during
    regeneration, we need to be able to get at all in-scope template
    parameters and corresponding template arguments during constraint
    checking of a lambda's op().  And this information is not easily
    available when we need it, it seems.

    To that end, the approach that this patch takes is to add two new fields
    to LAMBDA_EXPR (and remove one): LAMBDA_EXPR_REGENERATED_FROM
    (replacing LAMBDA_EXPR_INSTANTIATED), and LAMBDA_EXPR_REGENERATING_TARGS.
    The former allows us to obtain the complete set of template parameters
    that are in-scope for a lambda's op(), and the latter gives us all outer
    template arguments that were used to regenerate the lambda (analogous to
    the TI_TEMPLATE and TI_ARGS of a TEMPLATE_INFO, respectively).

    LAMBDA_EXPR_REGENERATING_TARGS is not strictly necessary -- in an
    earlier prototype, I walked LAMBDA_EXPR_EXTRA_SCOPE to build up this set
    of outer template arguments on demand, but it seems cleaner to do it this
    way.  (We'd need to walk LAMBDA_EXPR_EXTRA_SCOPE and not DECL/TYPE_CONTEXT
    because the latter skips over variable template scopes.)

    This patch also renames the predicate instantiated_lambda_fn_p to
    regenerated_lambda_fn_p, for sake of consistency with the rest of the
    patch which uses "regenerated" instead of "instantiated".

    gcc/cp/ChangeLog:

            PR c++/99874
            * constraint.cc (get_normalized_constraints_from_decl): Handle
            regenerated lambdas.
            (satisfy_declaration_constraints): Likewise.  Check for
            dependent args later.
            * cp-tree.h (LAMBDA_EXPR_INSTANTIATED): Replace with ...
            (LAMBDA_EXPR_REGENERATED_FROM): ... this.
            (LAMBDA_EXPR_REGENERATING_TARGS): New.
            (tree_lambda_expr::regenerated_from): New data member.
            (tree_lambda_expr::regenerating_targs): New data member.
            (add_to_template_args): Declare.
            (regenerated_lambda_fn_p): Likewise.
            (most_general_lambda): Likewise.
            * lambda.c (build_lambda_expr): Set LAMBDA_EXPR_REGENERATED_FROM
            and LAMBDA_EXPR_REGENERATING_TARGS.
            * pt.c (add_to_template_args): No longer static.
            (tsubst_function_decl): Unconditionally propagate constraints on
            the substituted function decl.
            (instantiated_lambda_fn_p): Rename to ...
            (regenerated_lambda_fn_p): ... this.  Check
            LAMBDA_EXPR_REGENERATED_FROM instead of
            LAMBDA_EXPR_INSTANTIATED.
            (most_general_lambda): Define.
            (enclosing_instantiation_of): Adjust after renaming
            instantiated_lambda_fn_p.
            (tsubst_lambda_expr): Don't set LAMBDA_EXPR_INSTANTIATED.  Set
            LAMBDA_EXPR_REGENERATED_FROM and LAMBDA_EXPR_REGENERATING_TARGS.
            Don't substitute or set constraints on the regenerated lambda.

    gcc/testsuite/ChangeLog:

            PR c++/99874
            * g++.dg/cpp2a/concepts-lambda16.C: New test.
            * g++.dg/cpp2a/concepts-lambda17.C: New test.

[Bug c++/99874] [11 Regression] ICE Segmentation fault when declared variable template of template lambda

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99874

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed, thanks for the bug report.