[clang] Missing llvm.lifetime.start/end intrinsics for temporary objects

Clang Frontend
1

Hi all,

for every stack variable, clang models the lifetime of the variable with llvm.lifetime.start and llvm.lifetime.end intrinsics.

I was a bit surprised that clang is not adding lifetime intrinsics for temporary objects that typically (except of lifetime extended temporaries) have a lifetime of the statement.

Example

In the following example, lifetime intrinsics are created for a A but not for the temporary object created within b(). See Compiler Explorer .

struct a {
  ~a();
};

a b();

int cond;

void f() {
  if (cond) {
    a A;
    b();
  }
}

Questions

  1. Is there a reason that no lifetime intrinsics are created for temporary objects? (a bug or a feature)
  2. Does clang give away optimization potential (e.g. for stack size) by not adding lifetime intrinsics for temporary objects?