RFR: 8358568: C2 compilation hits "must have a monitor" assert with -XX:-GenerateSynchronizationCode [v2]

[hanguanqiang]

> This PR fixes JDK-8358568, a JVM crash triggered when running with -XX:-GenerateSynchronizationCode
> 
> Problem：
> When synchronization code generation is disabled by -XX:-GenerateSynchronizationCode, the compiler’s do_monitor_exit() method still tries to access monitor objects without checking if any monitors exist.This causes an assertion failure and JVM crash.
> 
> Root Cause：
> Parse::do_monitor_exit() calls shared_unlock() using monitor info unconditionally,but with GenerateSynchronizationCode disabled, no monitor info is available, leading to invalid access.
> 
> Fix
> Add a check in do_monitor_exit() to skip monitor unlocking if GenerateSynchronizationCode is false, avoiding invalid monitor access and preventing the crash.

hanguanqiang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:

 - remove the unused flag(GenerateSynchronizationCode)
 - 8358568: C2 compilation hits "must have a monitor" assert with -XX:-GenerateSynchronizationCode
   
   This PR fixes JDK-8358568, a JVM crash triggered when running with -XX:-GenerateSynchronizationCode
   
   Problem：
   When synchronization code generation is disabled by -XX:-GenerateSynchronizationCode, the compiler’s do_monitor_exit() method still tries to access monitor objects without checking if any monitors exist.This causes an assertion failure and JVM crash.
   
   Root Cause：
   Parse::do_monitor_exit() calls shared_unlock() using monitor info unconditionally,but with GenerateSynchronizationCode disabled, no monitor info is available, leading to invalid access.
   
   Fix
   Add a check in do_monitor_exit() to skip monitor unlocking if GenerateSynchronizationCode is false, avoiding invalid monitor access and preventing the crash.

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Changes: https://git.openjdk.org/jdk/pull/26108/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26108&range=01
  Stats: 34 lines in 7 files changed: 10 ins; 16 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/26108.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26108/head:pull/26108

PR: https://git.openjdk.org/jdk/pull/26108