On Thu, 17 Nov 2022 09:23:48 GMT, Erik Österlund <eosterl...@openjdk.org> wrote:
>> src/hotspot/share/gc/shared/barrierSetStackChunk.cpp line 68:
>>
>>> 66:
>>> 67: virtual void do_oop(oop* p) override {
>>> 68: if (UseCompressedOops) {
>>
>> Wouldn't it be better to hoist the check for `UseCompressedOops`?
>
> The compiler should be able to do that already. We devirtualize calls into
> oop closures, and the closure is stack allocated. So the compiler should be
> able to do that if it finds that it is a good idea. I'd prefer to leave that
> to the compiler.
`CompressOopsOopClosure::do_oop()` and `FrameOopIterator::oops_do()` are
defined in different compilation units. So calls to `do_oop()` cannot be
devirtualized or am I missing something?
Mistaken or not, I'm ok with this version.
>> src/hotspot/share/gc/shenandoah/shenandoahBarrierSetStackChunk.cpp line 30:
>>
>>> 28:
>>> 29: void ShenandoahBarrierSetStackChunk::encode_gc_mode(stackChunkOop
>>> chunk, OopIterator* oop_iterator) {
>>> 30: // Nothing to do
>>
>> Shenandoah allows `UseCompressedOops` enabled, doesn't it? Isn't it
>> necessary then to do the encoding as in the super class?
>
> No we don't convert the oops for Shenandoah. Instead, Shenandoah's closures
> know how to deal with both oop* and narrowOop* on the heap, and will get
> passed the appropriate type of pointer. So it doesn't use the bitmap. I have
> tested that it works with Shenandoah as well.
Interesting and good to know.
-------------
PR: https://git.openjdk.org/jdk/pull/11111
