Integrated: 8341127: Extra call to MethodHandle::asType from memory segment var handles fails to inline

[Maurizio Cimadamore]

On Tue, 1 Oct 2024 10:08:54 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

> The fix for JDK-8331865 introduced an accidental performance regression.
> The main issue is that now *all* memory segment var handles go through some round of adaptation.
> Adapting a var handle results in a so called *indirect* var handle.
> When an indirect var handle is called through a *var handle guard*, an extra `MethodHandle::asType` call is triggered.
> In some cases, if `asType` has already been compiled into a big method, it cannot be inlined into the caller, which then results in a failure to inline through the var handle call, resulting in a big performance regression.
> 
> The solution is to make sure that the compiled size of `MethodHandle::asType` stays small: this is done by making sure that the slowpath (the one which populates the cache used by `asType`) is not inlined by the JVM. This is done by consolidating the slow path into a separate method, which is annotated with the internal `@DontInline` annotation.
> 
> This problem was originally reported here:
> https://mail.openjdk.org/pipermail/panama-dev/2024-September/020643.html
> 
> While we did not test this fix directly, we have made sure that running the problematic benchmark with the flags:
> 
> 
> -XX:CompileCommand=dontinline,java/lang/invoke/MethodHandle.setAsTypeCache
> -XX:CompileCommand=dontinline,java/lang/invoke/MethodHandle.asTypeUncached
> 
> 
> Solves the performance regression. The fix in this PR is just a programmatic way to achieve the same results w/o the need of command line flags.

This pull request has now been integrated.

Changeset: 7fa2f229
Author:    Maurizio Cimadamore <mcimadamore at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/7fa2f229fbee68112cbdd18b811d95721adfe2ec
Stats:     152 lines in 2 files changed: 150 ins; 0 del; 2 mod

8341127: Extra call to MethodHandle::asType from memory segment var handles fails to inline

Reviewed-by: psandoz, redestad, jvernee

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PR: https://git.openjdk.org/jdk/pull/21283