[jdk17] RFR: 8269304: Regression ~5% in 2005 in b27

[Dean Long]

On Sat, 26 Jun 2021 14:01:13 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> JDK-8268347 changes missed check for valid case when all locks/unlocks in coarsened group were eliminated.
> As result methods were recompiled without locks coarsening optimization leaving locks in code.
> 
> Tested tier1-3, xcomp, performance.

src/hotspot/share/opto/compile.cpp line 4519:

> 4517:     if (size == 0) {
> 4518:       unbalanced = false; // All locks were eliminated - good
> 4519:     } else if (size != locks_list->origin_cnt()) {

The size == 0 case makes sense.  Is there a possible situation where some locks were removed, but the remaining are still balanced?

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PR: https://git.openjdk.java.net/jdk17/pull/155