[16] RFR(S): 8248791: sun/util/resources/cldr/TimeZoneNamesTest.java fails with -XX:-ReduceInitialCardMarks -XX:-ReduceBulkZeroing

[Vladimir Kozlov]

Good.

Thanks,
Vladimir K

On 8/12/20 6:34 AM, Christian Hagedorn wrote:
> Hi
> 
> Please review the following patch:
> https://bugs.openjdk.java.net/browse/JDK-8248791
> http://cr.openjdk.java.net/~chagedorn/8248791/webrev.00/
> 
> The problem can be traced back to cloning an object and wrongly optimizing a field load from it to a constant zero. In 
> LoadNode::Value(), we check if a load is performed on a freshly-allocated object. If that is the case we can replace the 
> load by a constant zero. This is done by calling can_see_stored_value() at [1]. In this method, we first check if we can 
> find a captured store with find_captured_store() [2].
> 
> When enabling ReduceBulkZeroing in the testcase, then this method returns NULL because captured_store_insertion_point() 
> bails out at [3] for completed InitializationNodes (is set to complete at [4] since ReduceBulkZeroing is enabled and the 
> allocation belongs to a clone).
> 
> When disabling ReduceBulkZeroing in the testcase, find_caputured_store() returns a non-NULL ProjNode because the 
> InitializationNode of the allocation is not marked completed. We loop one more time and then return a constant zero at 
> [5] because there is no store for the allocation (the ArrayCopyNode is responsible for the initialization of the cloned 
> object).
> 
> The fix now only returns a constant zero if ReduceBulkZeroing is enabled or when the allocation does not belong to an 
> ArrayCopyNode clone (if ReduceBulkZeroing is disabled).
> 
> Thank you!
> 
> Best regards,
> Christian
> 
> 
> [1] http://hg.openjdk.java.net/jdk/jdk/file/e7109ed4bbb0/src/hotspot/share/opto/memnode.cpp#l1968
> [2] http://hg.openjdk.java.net/jdk/jdk/file/e7109ed4bbb0/src/hotspot/share/opto/memnode.cpp#l1115
> [3] http://hg.openjdk.java.net/jdk/jdk/file/e7109ed4bbb0/src/hotspot/share/opto/memnode.cpp#l3737
> [4] http://hg.openjdk.java.net/jdk/jdk/file/e7109ed4bbb0/src/hotspot/share/opto/library_call.cpp#l4236
> [5] http://hg.openjdk.java.net/jdk/jdk/file/e7109ed4bbb0/src/hotspot/share/opto/memnode.cpp#l1106