[Bug c++/123671] New: [16 Regression] ICE (Segmentation fault) in is_gimple_min_invariant when gimplifying lambda-within-template-default-argument

[jirehguo at tju dot edu.cn via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123671

            Bug ID: 123671
           Summary: [16 Regression] ICE (Segmentation fault) in
                    is_gimple_min_invariant when gimplifying
                    lambda-within-template-default-argument
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jirehguo at tju dot edu.cn
  Target Milestone: ---

Compiler Explorer: https://godbolt.org/z/78vj7oToa
The following c++ code crash gcc trunk with -std=c++23 flag.
But gcc 12,13,14,15 with checking is fine.

Code:
```cpp
struct S { int i; };

struct bad {
  template <auto L = [] {
    struct { S s; } ct;
    auto result = ct.s;
  }>
  static g() {
    L();
  }
};

int main() {
  bad::g();
}
```

Stack dump:
```
<source>:10:10: error: ISO C++ forbids declaration of 'g' with no type
[-fpermissive]
   10 |   static g() {
      |          ^
<source>: In instantiation of 'static int bad::g() [with auto L = <lambda
closure object>main()::<lambda()>()]':
required from here
<source>:15:9:   
   15 |   bad::g();
      |   ~~~~~~^~
<source>:12:3: warning: no return statement in function returning non-void
[-Wreturn-type]
   12 |   }
      |   ^
<source>: In lambda function:
<source>:8:36: internal compiler error: Segmentation fault
    8 |                   auto result = ct.func;
      |                                 ~~~^~~~
0x2950a78 diagnostics::context::diagnostic_impl(rich_location*,
diagnostics::metadata const*, diagnostics::option_id, char const*,
__va_list_tag (*) [1], diagnostics::kind)
        ???:0
0x294583b internal_error(char const*, ...)
        ???:0
0x114f894 is_gimple_min_invariant(tree_node const*)
        ???:0
0x11eb542 gimplify_expr(tree_node**, gimple**, gimple**, bool (*)(tree_node*),
int)
        ???:0
0x11ed5df gimplify_expr(tree_node**, gimple**, gimple**, bool (*)(tree_node*),
int)
        ???:0
0x12000f3 gimplify_arg(tree_node**, gimple**, unsigned long, bool)
        ???:0
0x11ec938 gimplify_expr(tree_node**, gimple**, gimple**, bool (*)(tree_node*),
int)
        ???:0
0x11ec987 gimplify_expr(tree_node**, gimple**, gimple**, bool (*)(tree_node*),
int)
        ???:0
0x11ef52a gimplify_stmt(tree_node**, gimple**)
        ???:0
0x11ec2db gimplify_expr(tree_node**, gimple**, gimple**, bool (*)(tree_node*),
int)
        ???:0
0x11ef52a gimplify_stmt(tree_node**, gimple**)
        ???:0
0x11ec7b0 gimplify_expr(tree_node**, gimple**, gimple**, bool (*)(tree_node*),
int)
        ???:0
0x11ef52a gimplify_stmt(tree_node**, gimple**)
        ???:0
0x11ec7b0 gimplify_expr(tree_node**, gimple**, gimple**, bool (*)(tree_node*),
int)
        ???:0
0x12109d6 gimplify_body(tree_node*, bool)
        ???:0
0x1210e9c gimplify_function_tree(tree_node*)
        ???:0
0xfc6c97 cgraph_node::analyze()
        ???:0
0xfca156 symbol_table::finalize_compilation_unit()
        ???:0
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
Compiler returned: 1
```