8361497: Scoped Values: orElse and orElseThrow do not access the cache

[theRealAph]

Neither ScopedValue.orElse nor ScopedValue.orElseThrow consult the cache when searching for a binding. Neither do they update the cache when a binding is found.
While this issue does not affect spec compliance, it is surprising to users that x.orElse(other) should be slower than x.isBound ? x.get() : other.

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Issue

• JDK-8361497: Scoped Values: orElse and orElseThrow do not access the cache (Bug - P4)

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[theRealAph]

I've also added some more performance tests to ensure that orElse() really does consult the cache.

[mlbridge]

Webrevs

• 00: Full (44b542e9)

[liach]

Can get and slowGet be refactored to use this findBinding too? That way we have just one piece of code accessing the cache, easier for long-term maintenance. get can probably become something like:

        var value = findBinding();
        if (value == Snapshot.NIL) {
            throw new NoSuchElementException("ScopedValue not bound");
        }
        return (T)value;

and remove slowGet altogether.

P.S. moved from inline comments, not really suitable for inline

[theRealAph]

Can get and slowGet be refactored to use this findBinding too?

Not really, no. Inlining is critical here, and get() is written in this way for efficiency of generated code.