[Bug c++/98326] New: ICE: in create_tmp_var, at gimple-expr.c:482, converting stateless generic-lambda to function pointer

[Bug c++/98326] New: ICE: in create_tmp_var, at gimple-expr.c:482, converting stateless generic-lambda to function pointer

[leni536 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98326

            Bug ID: 98326
           Summary: ICE: in create_tmp_var, at gimple-expr.c:482,
                    converting stateless generic-lambda to function
                    pointer
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: leni536 at gmail dot com
  Target Milestone: ---

version: g++ (Compiler-Explorer-Build) 10.2.0
arguments: -O2 -std=c++17 -pedantic-errors

```
struct A {
    A() = default;
    A(const A&) {}
};

void (*fptr)(A) = [](auto){};
```

<source>: In static member function 'static constexpr decltype
(((const<lambda(auto:1)>*)0)->operator()<auto:1>(static_cast<auto:1&&>(<anonymous>)))<lambda(auto:1)>::_FUN(auto:1)
[with auto:1 = A]':
<source>:6:28: internal compiler error: in create_tmp_var, at gimple-expr.c:482
    6 | void (*fptr)(A) = [](auto){};
      |                            ^


The ICE seems to happen when the by-value parameter's type is not trivially
copyable. It can also be reproduced with a non-trivial destructor.

If the copy-constructor is deleted then it fails to compile with a non-ice
error.

Related: PR 86943

In my understanding gcc tries to copy/move the by-value parameter in the free
function to pass it to `closure{}(args)`. I don't think that copying/moving the
by-value argument is correct. The effect of calling the resulting function
pointer should be equivalent to calling the operator() on the closure object,
it's not expressed in terms of forwarding the parameters:

https://timsong-cpp.github.io/cppwp/n4659/expr.prim.lambda.closure#8

It's more precisely spelled out in C++20, as there it can be expressed it in
terms of a default constructed object of the closure type:

http://eel.is/c++draft/expr.prim.lambda.closure#10.sentence-1

[Bug c++/98326] [10/11 Regression] ICE: in create_tmp_var, at gimple-expr.c:482, converting stateless generic-lambda to function pointer since r10-599-gc652ff8312433483

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98326

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Target Milestone|---                         |10.3
   Last reconfirmed|                            |2020-12-17
      Known to fail|                            |10.2.0, 11.0
      Known to work|                            |9.3.0
                 CC|                            |marxin at gcc dot gnu.org
           Keywords|                            |ice-on-valid-code
             Status|UNCONFIRMED                 |NEW
            Summary|ICE: in create_tmp_var, at  |[10/11 Regression] ICE: in
                   |gimple-expr.c:482,          |create_tmp_var, at
                   |converting stateless        |gimple-expr.c:482,
                   |generic-lambda to function  |converting stateless
                   |pointer                     |generic-lambda to function
                   |                            |pointer since
                   |                            |r10-599-gc652ff8312433483

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Confirmed, started with r10-599-gc652ff8312433483.

[Bug c++/98326] [10/11 Regression] ICE: in create_tmp_var, at gimple-expr.c:482, converting stateless generic-lambda to function pointer since r10-599-gc652ff8312433483

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98326

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

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

[Bug c++/98326] [10/11 Regression] ICE: in create_tmp_var, at gimple-expr.c:482, converting stateless generic-lambda to function pointer since r10-599-gc652ff8312433483

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98326

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

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, shouldn't either the cp/call.c change have been:
-           && ! TREE_ADDRESSABLE (TREE_TYPE (arg)))
+           && ! TREE_ADDRESSABLE (TREE_TYPE (arg))
+           && simple_empty_class_p (TREE_TYPE (arg), arg, INIT_EXPR))
rather than
-           && ! TREE_ADDRESSABLE (TREE_TYPE (arg)))
+           && simple_empty_class_p (TREE_TYPE (arg), arg, INIT_EXPR))
so it would don't try to handle TREE_ADDRESSABLE classes this way?
Or perhaps simple_empty_class_p should punt for TREE_ADDRESSABLE types?
In any case, passing CONSTRUCTOR with TREE_ADDRESSABLE type directly as
argument to function call leads to creating temporaries of the type, which
aren't allowed.

[Bug c++/98326] [10/11 Regression] ICE: in create_tmp_var, at gimple-expr.c:482, converting stateless generic-lambda to function pointer since r10-599-gc652ff8312433483

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98326

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++/98326] [10/11 Regression] ICE: in create_tmp_var, at gimple-expr.c:482, converting stateless generic-lambda to function pointer since r10-599-gc652ff8312433483

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98326

--- 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:bdbca69e0720fa9062fe71782235141f629ae006

commit r11-7142-gbdbca69e0720fa9062fe71782235141f629ae006
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Feb 8 17:04:03 2021 -0500

    c++: generic lambda, fn* conv, empty class [PR98326]

    Here, in the thunk returned from the captureless lambda conversion to
    pointer-to-function, we try to pass through invisible reference parameters
    by reference, without doing a copy.  The empty class copy optimization was
    messing that up.

    gcc/cp/ChangeLog:

            PR c++/98326
            PR c++/20408
            * cp-gimplify.c (simple_empty_class_p): Don't touch an invisiref
            parm.

    gcc/testsuite/ChangeLog:

            PR c++/98326
            * g++.dg/cpp1y/lambda-generic-empty1.C: New test.

[Bug c++/98326] [10/11 Regression] ICE: in create_tmp_var, at gimple-expr.c:482, converting stateless generic-lambda to function pointer since r10-599-gc652ff8312433483

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98326

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:031e97207463710797625382baff112b6c3ade51

commit r10-9362-g031e97207463710797625382baff112b6c3ade51
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Feb 8 17:04:03 2021 -0500

    c++: generic lambda, fn* conv, empty class [PR98326]

    Here, in the thunk returned from the captureless lambda conversion to
    pointer-to-function, we try to pass through invisible reference parameters
    by reference, without doing a copy.  The empty class copy optimization was
    messing that up.

    gcc/cp/ChangeLog:

            PR c++/98326
            PR c++/20408
            * cp-gimplify.c (simple_empty_class_p): Don't touch an invisiref
            parm.

    gcc/testsuite/ChangeLog:

            PR c++/98326
            * g++.dg/cpp1y/lambda-generic-empty1.C: New test.

[Bug c++/98326] [10/11 Regression] ICE: in create_tmp_var, at gimple-expr.c:482, converting stateless generic-lambda to function pointer since r10-599-gc652ff8312433483

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98326

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

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

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 10.3/11.