[Bug c++/126754] New: [16/17 Regression] ICE in tsubst_expr, at cp/pt.cc:23354

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126754

            Bug ID: 126754
           Summary: [16/17 Regression] ICE in tsubst_expr, at
                    cp/pt.cc:23354
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: haakonsv at gmail dot com
  Target Milestone: ---

Compiler Explorer: https://godbolt.org/z/av78K7nqc

The following code crashes GCC trunk. All versions of 16.X are affected, while
GCC 15.X and earlier versions are not affected.

I've tried bisecting GCC, it seems like
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=24efdb0974 is the first bad
commit.

Code:
```
struct S { int i; };
int main() {
    constexpr S a{1};
    const auto f = [](auto b) {
        return 1 - a.i;  // this expression must be independent of b in order
to trigger the crash
    };
    return f(0);
}
```

Stack dump:
```
<source>: In instantiation of 'main()::<lambda(auto:1)> [with auto:1 = int]':
<source>:7:13:   required from here
    7 |     return f(0);
      |            ~^~~
<source>:5:20: internal compiler error: in tsubst_expr, at cp/pt.cc:23354
    5 |         return 1 - a.i;  // this expression must be independent of b in
order to trigger the crash
      |                    ^
0x2b97f28 diagnostics::context::diagnostic_impl(rich_location*,
diagnostics::metadata const*, diagnostics::option_id, char const*,
__va_list_tag (*) [1], diagnostics::kind)
        ???:0
0x2b8cb6b internal_error(char const*, ...)
        ???:0
0xb40b7e fancy_abort(char const*, int, char const*)
        ???:0
0xdfb9ad instantiate_decl(tree_node*, bool, bool)
        ???:0
0xc60de3 maybe_instantiate_decl(tree_node*)
        ???:0
0xc62dc7 mark_used(tree_node*, int)
        ???:0
0xb7e593 build_op_call(tree_node*, vec<tree_node*, va_gc, vl_embed>**, int)
        ???:0
0xe3a3d6 finish_call_expr(tree_node*, vec<tree_node*, va_gc, vl_embed>**, bool,
bool, int)
        ???:0
0xd96823 c_parse_file()
        ???:0
0xf29cf9 c_common_parse_file()
        ???:0
```