[foreign-memaccess+abi] RFR: 8302346: Lift upcall sharing mechanism to AbstractLinker

[Maurizio Cimadamore]

On Tue, 14 Feb 2023 11:21:56 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> Lift the upcall sharing mechanism to AbstractLinker, where it can live next to the similar mechanism for down calls. This also allows the fallback linker to use this mechanism.
> 
> Instead of an upcall stub, AbstractLinker::arrangeDowncall now return an UpcallStubFactory, which is a callback accepting a target MethodHandle and Arena, which are then used to construct the actual upcall stub.
> 
> Perhaps the trickiest part of this patch is that we have to simulate the effects of `SharedUtils::adaptUpcallForIMR` on the target method type. I've added a new method in SharedUtils, called `computeUpcallIMRType` for that, which mimics the shape of the `adaptUpcallForIMR` method.
> 
> Since the shape of most of the arrangeUpcall methods was very similar, I factored them out into a helper method in SharedUtils as well.

src/java.base/share/classes/jdk/internal/foreign/abi/SharedUtils.java line 166:

> 164: 
> 165:     // this just computes the adjusted type
> 166:     private static MethodType computeUpcallIMRType(MethodType targetType, boolean dropReturn) {

Crazy idea - what if we created a fake method handle of the given target type - then just called adaptUpcallForIMR on it, and got the resulting type? I'm a bit worried for the type logic and the MH adaptation logic to go out of sync, and require changing things in two places.

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PR: https://git.openjdk.org/panama-foreign/pull/791