[Bug c++/94205] New: ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI

[Bug c++/94205] New: ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205

            Bug ID: 94205
           Summary: ICE in cxx_eval_constant_expression with
                    'this'-capturing lambda inside an NSDMI
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ppalka at gcc dot gnu.org
  Target Milestone: ---

$ cat ice.C
struct S
{
  int a = [this] { this->a = 5; return 6; } ();
};


constexpr S s = {};
$ g++ -std=c++2a ice.C
ice.C:7:18: internal compiler error: in cxx_eval_constant_expression, at
cp/constexpr.c:6176
    7 | constexpr S s = {};          
      |                  ^                                                      
0x5fe2d0 cxx_eval_constant_expression    
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:6176
0x941f5f cxx_eval_constant_expression
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:5700
0x9413d6 cxx_eval_constant_expression                                           
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:5965
0x94eacf cxx_eval_bare_aggregate
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:3836
0x941f0f cxx_eval_constant_expression                                           
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:5930
0x943e5b cxx_eval_constant_expression
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:5552
0x941f5f cxx_eval_constant_expression
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:5700
0x94f4f3 cxx_bind_parameters_in_call
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:1525
0x93eb25 cxx_eval_call_expression
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:2294
0x94177d cxx_eval_constant_expression                                           
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:5472
0x94eacf cxx_eval_bare_aggregate                                                
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:3836
0x941f0f cxx_eval_constant_expression
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:5930
0x944b74 cxx_eval_outermost_constant_expr
        /home/patrick/code/gcc-master/gcc/cp/constexpr.c:6486

[Bug c++/94205] [8/9/10 Regression] ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI since r8-1251

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org
     Ever confirmed|0                           |1
            Summary|ICE in                      |[8/9/10 Regression] ICE in
                   |cxx_eval_constant_expressio |cxx_eval_constant_expressio
                   |n with 'this'-capturing     |n with 'this'-capturing
                   |lambda inside an NSDMI      |lambda inside an NSDMI
                   |                            |since r8-1251
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2020-03-17
           Priority|P3                          |P2
   Target Milestone|---                         |8.5

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
ICEs since r8-1251-g948d0d9137b8df8320cae815fd8b8aba86bcc160 , before that it
has been rejected with -std=c++1z.

[Bug c++/94205] [8/9/10 Regression] ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI since r8-1251

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205

Jason Merrill <jason at gcc dot gnu.org> changed:

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

[Bug c++/94205] [8/9/10 Regression] ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI since r8-1251

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
C++14 version that goes back to the introduction of C++14 constexpr in GCC 5:

struct S
{
  struct A
  {
    S *p;
    constexpr A(S* p): p(p) {}
    constexpr operator int() { p->a = 5; return 6; }
  };
  int a = A(this);
};


constexpr S s = {};

#define SA(X) static_assert((X),#X)
SA(s.a == 6);

[Bug c++/94205] [8/9/10 Regression] ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI since r8-1251

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:76f09260b7eccd6c3cfa3dcf3c22897fe12a8065

commit r10-7490-g76f09260b7eccd6c3cfa3dcf3c22897fe12a8065
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Mar 31 17:34:47 2020 -0400

    c++: Fix DMI with lambda 'this' capture [PR94205]

    We represent 'this' in a default member initializer with a
PLACEHOLDER_EXPR.
    Normally in constexpr evaluation when we encounter one it refers to
    ctx->ctor, but when we're creating a temporary of class type, that replaces
    ctx->ctor, so a PLACEHOLDER_EXPR that refers to the type of the member
being
    initialized needs to be replaced before that happens.

    gcc/cp/ChangeLog
    2020-03-31  Jason Merrill  <jason@redhat.com>

            PR c++/94205
            * constexpr.c (cxx_eval_constant_expression) [TARGET_EXPR]: Call
            replace_placeholders.
            * typeck2.c (store_init_value): Fix arguments to
            fold_non_dependent_expr.

[Bug c++/94205] [8/9/10 Regression] ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI since r8-1251

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|jason at gcc dot gnu.org           |unassigned at gcc dot gnu.org

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> ---
Patrick is working on the remaining parts of this bug.

[Bug c++/94205] [8/9/10 Regression] ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI since r8-1251

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205

--- 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:37244b217a7329792f4ec48027f63cf5010b0ea8

commit r10-7556-g37244b217a7329792f4ec48027f63cf5010b0ea8
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Apr 2 12:59:34 2020 -0400

    c++: Fix constexpr evaluation of self-modifying CONSTRUCTORs [PR94219]

    This PR reveals that cxx_eval_bare_aggregate and cxx_eval_store_expression
do
    not anticipate that a constructor element's initializer could mutate the
    underlying CONSTRUCTOR.  Evaluation of the initializer could add new
elements to
    the underlying CONSTRUCTOR, thereby potentially invalidating any pointers
to
    or assumptions about the CONSTRUCTOR's elements, and so these routines
should be
    prepared for that.

    To fix this problem, this patch makes cxx_eval_bare_aggregate and
    cxx_eval_store_expression recompute the constructor_elt pointers through
which
    we're assigning, after it evaluates the initializer.  Care is taken to to
not
    slow down the common case where the initializer does not modify the
underlying
    CONSTRUCTOR.

    gcc/cp/ChangeLog:

            PR c++/94219
            PR c++/94205
            * constexpr.c (get_or_insert_ctor_field): Split out (while adding
            support for VECTOR_TYPEs, and optimizations for the common case)
            from ...
            (cxx_eval_store_expression): ... here.  Rename local variable
            'changed_active_union_member_p' to 'activated_union_member_p'. 
Record
            the sequence of indexes into 'indexes' that yields the subobject
we're
            assigning to.  Record the integer offsets of the constructor
indexes
            we're assigning through into 'index_pos_hints'.  After evaluating
the
            initializer of the store expression, recompute 'valp' using
'indexes'
            and using 'index_pos_hints' as hints.
            (cxx_eval_bare_aggregate): Tweak comments.  Use
get_or_insert_ctor_field
            to recompute the constructor_elt pointer we're assigning through
after
            evaluating each initializer.

    gcc/testsuite/ChangeLog:

            PR c++/94219
            PR c++/94205
            * g++.dg/cpp1y/constexpr-nsdmi3.C: New test.
            * g++.dg/cpp1y/constexpr-nsdmi4.C: New test.
            * g++.dg/cpp1y/constexpr-nsdmi5.C: New test.
            * g++.dg/cpp1z/lambda-this5.C: New test.

[Bug c++/94205] [8/9/10 Regression] ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI since r8-1251

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205

--- Comment #6 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:49a86fce1a879a206fb4b27f097910005d968fda

commit r10-7557-g49a86fce1a879a206fb4b27f097910005d968fda
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Apr 2 16:03:18 2020 -0400

    c++: Refrain from using replace_placeholders in constexpr evaluation
[PR94205]

    This removes the use of replace_placeholders in
cxx_eval_constant_expression
    (which is causing the new test lambda-this6.C to ICE due to
replace_placeholders
    mutating the shared TARGET_EXPR_INITIAL tree which then trips up the
    gimplifier).

    In its place, this patch adds a 'parent' field to constexpr_ctx which is
used to
    store a pointer to an outer constexpr_ctx that refers to another object
under
    construction.  With this new field, we can beef up lookup_placeholder to
resolve
    PLACEHOLDER_EXPRs which refer to former objects under construction, which
fixes
    PR94205 without needing to do replace_placeholders.  Also we can now
respect the
    CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag when resolving PLACEHOLDER_EXPRs, and
    doing so fixes the constexpr analogue of PR79937.

    gcc/cp/ChangeLog:

            PR c++/94205
            PR c++/79937
            * constexpr.c (struct constexpr_ctx): New field 'parent'.
            (cxx_eval_bare_aggregate): Propagate
CONSTRUCTOR_PLACEHOLDER_BOUNDARY
            flag from the original constructor to the reduced constructor.
            (lookup_placeholder): Prefer to return the outermost matching
object
            by recursively calling lookup_placeholder on the 'parent' context,
            but don't cross CONSTRUCTOR_PLACEHOLDER_BOUNDARY constructors.
            (cxx_eval_constant_expression): Link the 'ctx' context to the
'new_ctx'
            context via 'new_ctx.parent' when being expanded without an
explicit
            target.  Don't call replace_placeholders.
            (cxx_eval_outermost_constant_expr): Initialize 'ctx.parent' to
NULL.

    gcc/testsuite/ChangeLog:

            PR c++/94205
            PR c++/79937
            * g++.dg/cpp1y/pr79937-5.C: New test.
            * g++.dg/cpp1z/lambda-this6.C: New test.

[Bug c++/94205] [8/9/10 Regression] ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI since r8-1251

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205
Bug 94205 depends on bug 94219, which changed state.

Bug 94219 Summary: ICE in cxx_eval_bare_aggregate, at cp/constexpr.c:3790
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94219

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

[Bug c++/94205] [8/9 Regression] ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI since r8-1251

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[8/9/10 Regression] ICE in  |[8/9 Regression] ICE in
                   |cxx_eval_constant_expressio |cxx_eval_constant_expressio
                   |n with 'this'-capturing     |n with 'this'-capturing
                   |lambda inside an NSDMI      |lambda inside an NSDMI
                   |since r8-1251               |since r8-1251

--- Comment #7 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 10 so far.

[Bug c++/94205] [9 Regression] ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI since r8-1251

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|8.5                         |9.4

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 8 branch is being closed.

[Bug c++/94205] [9 Regression] ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI since r8-1251

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.4                         |9.5

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.

[Bug c++/94205] [9 Regression] ICE in cxx_eval_constant_expression with 'this'-capturing lambda inside an NSDMI since r8-1251

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94205

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to fail|                            |9.5.0
   Target Milestone|9.5                         |10.0
         Resolution|---                         |FIXED

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed in GCC 10.