Background:

The AOT Assembly Phase is in essence a small Java program that executes a limited set of Java bytecodes. This program bootstraps the module system, loads classes, and performs certain ahead-of-time optimizations such as resolving invokedynamic call sites.

As a side effect of Java program execution, a small set of Java classes are initialized in the Assembly Phase.

Since JDK-8360163, if a class X is annotated with @AOTSafeClassInitializer *and* is initialized in the Assembly Phase, then X will be stored in the AOT cache in the "initialized" state. In the Production Run, X.<clinit> will not be executed, and the static variables of X will be available upon JVM bootstrap.

Problem:
The Assembly Phase doesn't touch many classes that may benefit from @AOTSafeClassInitializer. For example, jdk.internal.math.MathUtils::<clinit> creates a few large tables. Caching MathUtils in the "initialized" state will improve start-up time. However, since no bytecodes executed by the Assembly Phase use MathUtils. it will not be initialized.

Proposal:
If a class X has the @AOTSafeClassInitializer annotation *and* was initialized in the AOT Training Run, the JVM should proactively initialize X in the Assembly Phase. This will ensure that X will be cached in the "initialized" state.

This RFE will implement the proposal. It will also add @AOTSafeClassInitializer to MathUtils as a proof of concept.

@AOTSafeClassInitializer will be added to more classes in future RFEs.