RFR: 8267947: CI: Preserve consistency between has_subklass() and is_subclass_of()

[Vladimir Ivanov]

On Tue, 1 Jun 2021 07:20:43 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> CI caches `Klass::subklass() != NULL` query, but concurrent class loading can
>> invalidate the cached value. Though recorded dependency won't let the nmethod
>> to be installed, the inconcistency can manifest as type paradoxes until
>> compilation is finished. 
>> 
>> The fix caches only `true` value (since it can't change unless class unloading
>> takes place) and queries the VM otherwise.
>> 
>> Testing:
>> - [x] hs-tier1 - hs-tier6
>
> src/hotspot/share/ci/ciKlass.cpp line 82:
> 
>> 80: 
>> 81: #ifdef ASSERT
>> 82:   if (that->is_instance_klass() && !that->is_interface()) {
> 
> Why the !that->is_interface() test?

`ciInstanceKlass::has_subklass()` is always `false` for interfaces because they always have `Klass::_subklass == NULL`.

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PR: https://git.openjdk.java.net/jdk/pull/4269