This effectively reverts the combined
<https://bugs.openjdk.java.net/browse/JDK-8157225> and
<https://bugs.openjdk.java.net/browse/JDK-8157250>.
That was not the intent of 8157251, though.
The intent of 8157251 was to use MethodHandles.arrayLength(Object[].class) for
all arrays with components of reference type (and use
ValidationType.INSTANCE_OF for it, as all such arrays will be instance-of
Object[] through instance-of semantics for array types) and leave the linking
of arrays with primitive component types as they are today.
So, basically, something like:
if(clazz.isArray()) {
// Some languages won't have a notion of manipulating collections. Exposing
"length" on arrays as an
// explicit property is beneficial for them.
if (clazz.getComponentType().isPrimitive()) {
setPropertyGetter("length", MethodHandles.arrayLength(clazz),
ValidationType.EXACT_CLASS);
} else {
setPropertyGetter("length", MethodHandles.arrayLength(Object[].class),
ValidationType.INSTANCE_OF);
}
Obviously, this is again a tradeoff between linkage stability and performance,
except that with this solution we don’t sacrifice any performance and we still
increase linkage stability. Going back to Array.getLength does further increase
linkage stability, but *speculatively* it doesn’t intrinsify to as lean code as
MethodHandles.arrayLength does (it certainly erases the type information of the
argument); someone with time on their hands should probably run some
PrintAssembly tests with -XX:-TieredCompilation to see whether this is true (if
not, then 8157225 and 8157250 were done for nothing and this patch undoes them
anyway).
In any case, I don’t have a too strong opinion about this; I don’t mind even if
this ends up being a reversal of 8157225; it’s just weird that we have
arrayLength method handle intrinsics and not use them.
Attila.
> On Jan 9, 2018, at 8:00 AM, Priya Lakshmi Muthuswamy
> <[email protected]> wrote:
>
> Hi,
>
> Please review JDK-8157251 : BeanLinker relinks array length operations for
> array types
>
> JBS : https://bugs.openjdk.java.net/browse/JDK-8157251
> webrev : http://cr.openjdk.java.net/~pmuthuswamy/8157251/webrev.00/
>
> Thanks,
> Priya
