[[lifetimebound]] basic members tracking

[DenisYaroshevskiy]

Hi!

Would be amazing if the following is caught to:

https://godbolt.org/z/5ze9s5roj

#include <utility>

struct Struct {
  std::pair<int, int> member;

  const auto* foo() const [[clang::lifetimebound]] { return &member; }
};

int main() {
  // auto& caught = *Struct().foo();
  auto& not_caught = Struct().foo()->second;  // this is a bug
  (void)not_caught;
}

[dwblaikie]

Does still repro with a trivial struct too, without the dependence on std::pair/standard library, fwiw: https://godbolt.org/z/5Ev65ha6z

[usx95]

Using a member function (instead of data member) which is annotated with [[clang::lifetimebound]] makes it work.

struct s {
    int first;
    int second;
    int& getFirst() [[clang::lifetimebound]] { return first; }
};
struct Struct {
    s member;

    s* foo() [[clang::lifetimebound]] { return &member; }
};

int main() {
    auto& caught = Struct().foo()->getFirst();  // this is a bug
    (void)caught;
}

I think we should consider field access as ~lifetimebound to make this work.

[DenisYaroshevskiy]

Thank you very much! Looking forward fo rthis being available in my compiler

[usx95]

/cherry-pick 1feef92