On Fri, 21 Feb 2025 10:12:45 GMT, Maurizio Cimadamore <mcimadam...@openjdk.org>
wrote:
>> Simplify the layout access var handles to be direct in some common cases.
>> Also made `VarHandle::isAccessModeSupported` report if an access mode is
>> supported for a VH.
>>
>> Reduces the instructions to execute this code in a simple main by 47%:
>>
>> long[] arr = new long[8];
>> var ms = MemorySegment.ofArray(arr);
>> ms.setAtIndex(ValueLayout.JAVA_BYTE, 12, (byte) 3);
>>
>>
>> Main overheads in FFM are identified to be:
>> 1. Eager initialization of direct MethodHandle; can be CDS archived
>> 2. MH combinator forms via LambdaFormEditor, not cached right now and always
>> have large overhead
>>
>> Still need other measures to deal with common user patterns of
>> `MethodHandles.insertCoordinates(vh, 1, 0L)` which currently is still very
>> slow.
>>
>> Tests: 2 unrelated failures on tier 1-3
>
> src/java.base/share/classes/java/lang/invoke/X-VarHandleSegmentView.java.template
> line 77:
>
>> 75: }
>> 76:
>> 77: @ForceInline
>
> Question: can this and the `offset` method go in the
> `VarHandleSegmentViewBase` class? They don't seem to depend on anything in
> these classes - so it seems mostly duplicated code?
Now this will require code update to static import `offset` from
`VarHandleSegmentViewBase`. Is that acceptable?
> src/java.base/share/classes/jdk/internal/foreign/layout/ValueLayouts.java
> line 164:
>
>> 162: @ForceInline
>> 163: public final VarHandle varHandle() {
>> 164: record VarHandleCache() implements
>> Function<AbstractValueLayout<?>, VarHandle> {
>
> Can this cache be removed? The var handles created here should be "direct" --
> meaning that we don't expect LayoutPath to add any adaptations on top of
> what's already done in the "raw" var handle returned by
> `Utils:makeRawSegmentViewVarHandle`?
We have two caches, one in `ValueLayouts` and another in `Utils`. Should we
remove both?
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/23720#discussion_r1965763775
PR Review Comment: https://git.openjdk.org/jdk/pull/23720#discussion_r1965771047
