This is an alternative to https://github.com/openjdk/jdk/pull/27024. Thanks to @ashu-mehra for the suggestion.
### 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](https://bugs.openjdk.org/browse/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. When the AOT cache is used 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. ### Fix: If a class `X` has the `@AOTSafeClassInitializer` annotation *and* was initialized in the AOT Training Run, the JVM will proactively initialize `X` in the Assembly Phase. This will ensure that `X` will be cached in the "initialized" state. As a proof of concept, `@AOTSafeClassInitializer` is added to `MathUtils`. `@AOTSafeClassInitializer` will be added to more classes in future RFEs. ------------- Commit messages: - updated javadoc for AOTSafeClassInitializer.java - Fix - imported Changes: https://git.openjdk.org/jdk/pull/27402/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27402&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8368174 Stats: 288 lines in 11 files changed: 196 ins; 47 del; 45 mod Patch: https://git.openjdk.org/jdk/pull/27402.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/27402/head:pull/27402 PR: https://git.openjdk.org/jdk/pull/27402
