RFR: 8138659: Speed up InstanceKlass subclass discrimination

[Coleen Phillimore]

In 
http://cr.openjdk.java.net/~kbarrett/8138659/webrev.00/src/share/vm/oops/instanceKlass.hpp.udiff.html

There are right_n_bits() and bitfield functions in globalDefinitions.hpp 
that would make some bit manipulation in this set_kind() easier to read.

Minor comment: I'd put kind_is_instance() .. kind_is_class_loader() 
functions on one line each and not use so much vertical space.

This is all I have to comment.  It looks like a good change to me.

Coleen

On 10/3/15 2:26 PM, Kim Barrett wrote:
> Please review this change to speed up discrimination among the classes
> rooted at InstanceKlass.
>
> We use 2 bits from InstanceKlass::_misc_flags (the _misc_kind field)
> for discrimination among the four kinds of InstanceKlass.  We use the
> low 2 bits of _misc_flags 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
> _misc_kind field. Updated all callers to provide the appropriate
> value.
>
> With these changes we can use the layout_helper-based
> Klass::oop_is_instance to get to the InstanceKlass case, and use the
> _misc_kind value to further discriminate from there.  In particular,
> the concrete InstanceKlass case is (after inlining)
>
>    (klass->_layout_helper > 0) &&
>    ((static_cast<InstanceKlass*>(klass)->_misc_flags & 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::oop_is_instanceXXX to instead call
> Klass::oop_is_instance then cast to InstanceKlass and use the
> corresponding kind_is_xxx predicate.  Removed the no longer used
> Klass::oop_is_instanceXXX 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/
>
> Testing:
> JPRT
> Aurora ad-hoc defaults + GC Nightly + Runtime Nightly
>