RFR: 8138659: Speed up InstanceKlass subclass discrimination (original) (raw)

Stefan Karlsson stefan.karlsson at oracle.com
Mon Oct 5 08:03:10 UTC 2015

Hi Kim,

On 2015-10-03 20:26, Kim Barrett wrote:

Please review this change to speed up discrimination among the classes rooted at InstanceKlass.

We use 2 bits from InstanceKlass::miscflags (the misckind field) for discrimination among the four kinds of InstanceKlass. We use the low 2 bits of miscflags to avoid a shift when accessing the field. This means that all the existing flags are being shifted up 2 bits. Added an accessor and a suite of predicates to InstanceKlass. Added kind argument to InstanceKlass constructor, which is used to set the misckind field. Updated all callers to provide the appropriate value. With these changes we can use the layouthelper-based Klass::oopisinstance to get to the InstanceKlass case, and use the misckind value to further discriminate from there. In particular, the concrete InstanceKlass case is (after inlining) (klass->layouthelper > 0) && ((staticcast<InstanceKlass*>(klass)->miscflags & 3) == 0) We could do better with a single discriminator, but there doesn't appear to be a good place to add such in Klass, and we don't want to make Klass bigger. Changed calls to Klass::oopisinstanceXXX to instead call Klass::oopisinstance then cast to InstanceKlass and use the corresponding kindisxxx predicate. Removed the no longer used Klass::oopisinstanceXXX functions. Removed unused InstanceRefKlass::cast. InstanceMirrorKlass::cast is retained because it is used. InstanceClassLoaderKlass::cast does not exist. CR: https://bugs.openjdk.java.net/browse/JDK-8138659 Webrev: http://cr.openjdk.java.net/~kbarrett/8138659/webrev.00/

Did you consider keeping the "kind" infrastructure within the instanceKlass files instead of letting it leak down into oop.inline.hpp and out to the rest of the runtime?

Could be:

bool oop_is_instanceClassLoader() const { return oop_is_instance() && InstanceKlass::cast(k)->oop_is_class_loader(); } bool oop_is_instanceMirror() const { return oop_is_instance() && InstanceKlass::cast(k)->oop_is_mirror(); } bool oop_is_instanceRef() const { return oop_is_instance() && InstanceKlass::cast(k)->oop_is_reference(); }

and then the following change would be unnecessary:

+ assert(InstanceKlass::cast(SystemDictionary::Class_klass())->kind_is_mirror(), "Is not?");

Other than that, this looks good to me.

StefanK

Testing: JPRT Aurora ad-hoc defaults + GC Nightly + Runtime Nightly

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