RFR: 8339299: C1 will miss type profile when inline final method [v3]

[kuaiwei]

On Fri, 6 Sep 2024 22:28:51 GMT, Dean Long <dlong at openjdk.org> wrote:

> Thinking about this a little more, I think the real problem is the choice of callee Method* passed to profile_call(). For the non-inlined case, cha_monomorphic_target is not used as the callee, but it is used for the holder. For the inlined case, we do pass cha_monomorphic_target as the callee for profile_call(). If we passed the resolved/selected Method* to try_inline() as an additional parameter to be used by profile_call(), then I believe the problem with can_be_statically_bound() goes away, and should_profile_receiver_type() will approximate what the interpreter does, which was the original intent.

Hi Dean, I'm not familiar with c1 profile. IMO, the original idea is if c1 can know callee is static bound, c2 can make the same decision. So c1 needn't do profile. I just think there may be another case to break it.

void A() {
   Child1 p = new Child1();
   return B(p);
}

void B(Parent p) {
  return C(p);
}

void C(Parent p) {
  return p.function();
}

If C1 decide to inline A->B->C, it can know p in C is exact type of Child1. And it can skip profile if Child1::function is final. But when C2 compile B, it can not get the profile data.
My think is there may be much cases to think about. We can just simply do profile in c1.

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PR Comment: https://git.openjdk.org/jdk/pull/20786#issuecomment-2337292634