[tysan] False positive with placement new

[zygoloid]

Testcase:

#include <new>

struct X {
  X *p;
};
struct Y {
  Y *p;
};
union U {
  X head;
  Y tail;
};

int main() {
  U u;
  new (&u) X{.p = 0};
  new (&u) Y{.p = 0};
}

(reduced from libc++'s std::variant implementation). This results in a false-positive diagnostics with -fsanitize=type:

==1==ERROR: TypeSanitizer: type-aliasing-violation on address 0x7fffaf0dc548 (pc 0x5e6468605ff7 bp 0x7fffaf0dc4f0 sp 0x7fffaf0dc480 tid 1)
WRITE of size 8 at 0x7fffaf0dc548 with type p1 _ZTS1Y (in Y at offset 0) accesses an existing object of type p1 _ZTS1X (in X at offset 0)
    #0 0x5e6468605ff6  (/app/output.s+0x2aff6)

Adding an explicit u.head.~X() call before the second placement new doesn't make a difference. Presumably type sanitizer isn't properly modeling new expressions (nor destructor / pseudo-destructor calls).

[Jannik2099]

duplicate of #120987