RFR: 8346567: Make Class.getModifiers() non-native

[Dan Heidinga]

On Mon, 9 Dec 2024 19:26:53 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> The Class.getModifiers() method is implemented as a native method in java.lang.Class to access a field that we've calculated when creating the mirror.  The field is final after that point. The VM doesn't need it anymore, so there's no real need for the jdk code to call into the VM to get it.  This moves the field to Java and removes the intrinsic code.  I promoted the compute_modifiers() functions to return int since that's how java.lang.Class uses the value.  It should really be an unsigned short though.
> 
> There's a couple of JMH benchmarks added with this change.  One does show that for array classes for non-bootstrap class loader, this results in one extra load which in a long loop of just that, is observable.  I don't think this is real life code. The other benchmarks added show no regression.
> 
> Tested with tier1-8.

src/java.base/share/classes/java/lang/Class.java line 244:

> 242:         classLoader = loader;
> 243:         componentType = arrayComponentType;
> 244:         modifiers = 0;

The comment above about assigning a parameter to the field to prevent the JIT from assuming an incorrect default also should apply to the new `modifiers` field.  I think the constructor, which is never called, should also pass in a `dummyModifiers` value rather than using 0 directly

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PR Review Comment: https://git.openjdk.org/jdk/pull/22652#discussion_r1880689835