MethodHandles.constant not inlining?

[John Rose]

On Jun 7, 2011, at 3:38 PM, Charles Oliver Nutter wrote:

> So I figured I'd check assembly output, and I was surprised to see a
> callq right where I expect to see the literal. Are
> MethodHandle.constant handles not inlined right now?

Here is what constant(Object.class, foo) reduces to:
  #wellKnownIdentityFn.bindTo(foo)

This should inline very nicely.

What is the type you pass to MHs.constant?  If it's not Object, call it T.

In the case of a type other than Object, we have:
  rawRetype(#wellKnownIdentityFn, methodType(T, T)).bindTo(foo)

where rawRetype is an internal trusted constructor which asserts that the result is trusted to be T, not just Object.  This should inline also.  There's a potential problem here:  The methodHandleWalk module will emit a return of an Object value (from wellKnownIdentityFn, not its real name) from an adapter that returns a value of type T.  This bytecode would be rejected by the verifier, but I don't think the verifier runs on MH graphs.

Maybe the methodHandleWalk modules is tripping over some aspect of this MH graph or the resulting bytecode.

-- John