[Bug tree-optimization/96963] [10 Regression] -Wstringop-overflow false positive on -O3 or -O2 -ftree-vectorize when assigning consecutive char struct members

[pokechu022+gccbugzilla at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96963

Pokechu22 <pokechu022+gccbugzilla at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |pokechu022+gccbugzilla@gmai
                   |                            |l.com

--- Comment #16 from Pokechu22 <pokechu022+gccbugzilla at gmail dot com> ---
I ran into this with Dolphin Emulator (see
https://github.com/dolphin-emu/dolphin/pull/11534), but ran into trouble trying
to simplify it. Here's what I ended up with:

```
struct Foo {
    char pad[40];
    char a, b;
};
struct Bar {
  void Baz();
  // One of these needs to be uncommented for the issue to occur
  // virtual void Qux();
  // int x;
  Foo foo;
};
void heh(char *);
void Bar::Baz() {
  heh(&foo.a);
  foo.a = 1;
  foo.b = 1;
}
```

Based on Godbolt (https://godbolt.org/z/46aTrP3vj) I can confirm that this
doesn't happen in 11.0 or 9.3/9.5, and does happen on 10.1/10.2/10.3/10.4.