[13] RFR(S): 8218201: Failures when vmIntrinsics::_getClass is not inlined

dean.long at oracle.com dean.long at oracle.com
Thu Mar 7 19:20:07 UTC 2019

I agree.  We don't want obj.getClass() to treat obj as "global escape".


PS - Original change goes back to JDK-6488063.

On 3/7/19 10:46 AM, Vladimir Kozlov wrote:
> _getClass is special case because it is native call and we can't do 
> bytecode analysis.
> But we know what it does (it loads klass from object and mirror from 
> klass) - no allocations, no locals, no arguments returned.
> I think it is simple missing _return_allocated = false setting in 
> addition to _return_local = false. _return_allocated is set to true by 
> default optimistically.
> Thanks,
> Vladimir
> On 3/7/19 4:54 AM, Tobias Hartmann wrote:
>> Hi,
>> please review the following patch:
>> https://bugs.openjdk.java.net/browse/JDK-8218201
>> http://cr.openjdk.java.net/~thartmann/8218201/webrev.00/
>> When intrinsification is disabled, the BCEscapeAnalyzer marks the 
>> return value of the (native)
>> method Object::getClass as "return allocated value" which means that 
>> "only newly allocated unescaped
>> objects are returned". The OptimizePtrCompare optimization then uses 
>> this information to incorrectly
>> fold 'obj.getClass() == Object.class' (see TestGetClass.java:39) to 
>> always false.
>> This is a very old issue and I can't trace back why a special case 
>> for the _getClass intrinsic has
>> been added to the BCEscapeAnalyzer. Since I don't think we should 
>> make any assumptions about the
>> returned Object, I've removed the special case.
>> Thanks,
>> Tobias

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