[Bug c++/117651] New: Read of an uninitialized subobject not detected in constant expression

[fchelnokov at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117651

            Bug ID: 117651
           Summary: Read of an uninitialized subobject not detected in
                    constant expression
           Product: gcc
           Version: 14.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fchelnokov at gmail dot com
  Target Milestone: ---

This program
```
struct B { 
    int v;
};

constexpr B g() { B b; return b; }
static_assert( g().v == 0 );
```
must fail because v-subobject is not initialized, and it does so in Clang and
MSVC. Unfortunately, GCC accepts the program just fine. Online demo:
https://gcc.godbolt.org/z/5Kbqxjrej