RFR: 8160821: VarHandle accesses are penalized when argument conversion is required [v3]

[Vladimir Ivanov]

On Mon, 1 Dec 2025 23:41:04 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Since access descriptor is created for each VH operation site, we can optimistically cache the adapted method handle in a site if the site operates on a constant VH.  Used a C2 IR test to verify such a setup through an inexact VarHandle invocation can be constant folded through (previously, it was blocked by `asType`)
>
> Chen Liang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Tweak VH usage in some classes

src/java.base/share/classes/java/lang/invoke/VarHandle.java line 2042:

> 2040:             // This is still a hot path if vh is not constant - in this case,
> 2041:             // asType is the bottleneck for constant folding, unfortunately
> 2042:             var result = vh.getMethodHandle(mode).asType(symbolicMethodTypeInvoker);

`mode` and `symbolicMethodTypeInvoker` are part of `AccessDescriptor` while `vh` comes as an argument. What guarantees that a cached adapter is compatible with `vh` observed during subsequent calls? It means that `vh` shape stays exactly the same shape. Is it correct? Would be good to have it validated with asserts.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28585#discussion_r2582661917