Integrated: 8322743: C2: prevent lock region elimination in OSR compilation

[Vladimir Kozlov]

On Tue, 9 Jan 2024 22:57:27 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> Corner case with a local (not escaped) object used for synchronization. C2 Escape Analysis thinks that it can eliminate locks for it. In most cases it is true but not in this case.
> 
> 
>         for (int i = 0; i < 2; ++i) {
>             Object o = new Object();
>             synchronized (o) { // monitorenter
>                 // Trigger OSR compilation
>                 for (int j = 0; j < 100_000; ++j) {
> 
> The test has nested loop which trigger OSR compilation. The locked object comes from Interpreter into compiled OSR code. During parsing C2 creates an other non escaped object and correctly merge both together (with Phi node) so that non escaped object is not scalar replaceable. Because it does not globally escapes EA still removes locks for it and, as result, also for merged locked object from Interpreter which is the bug.
> 
> The fix is to mark BoxLock node associated with OSR entry as Unbalanced to prevent EA from removing locks/unlocks from it. It is based on [JDK-8324969](https://github.com/openjdk/jdk/pull/17697) changes.
> 
> Added regression test prepared by @TobiHartmann. Tested tier1-5, xcomp and stress.
> Performance testing show no difference.

This pull request has now been integrated.

Changeset: 742c776a
Author:    Vladimir Kozlov <kvn at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/742c776a922bc226a3beaa9e219ff0bd2baf7bc4
Stats:     97 lines in 3 files changed: 94 ins; 1 del; 2 mod

8322743: C2: prevent lock region elimination in OSR compilation

Reviewed-by: epeter, dlong, vlivanov

-------------

PR: https://git.openjdk.org/jdk/pull/17331