Final CONSTANT_Dynamic spec

[Dan Smith]

> On Jan 18, 2018, at 5:14 PM, Dan Smith <daniel.smith at oracle.com> wrote:
> 
> A proposed final spec for CONSTANT_Dynamic is here:
> 
> http://cr.openjdk.java.net/~dlsmith/constant-dynamic.html
> 
> There are two significant changes:
> 
> 5.4.3: Expanded the rule about concurrent resolution to account for nested resolution in a single thread
> 
> 5.4.3.6: Added a resolution-time rule for detecting cycles in static arguments, with some additional discussion about cycles

Discussing this cycle-detection rule with Alex, we agreed that its nondeterminism was not helpful, and that we can make it deterministic without putting undue constraints on implementations. So here's a tweaked version of the rule we'd like to use instead:

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Let X be the symbolic reference currently being resolved, and let Y be a static argument of X to be resolved as described above. If X and Y are both dynamically-computed constants, and if Y is either the same as X or has a static argument that references X through its static arguments, directly or indirectly, resolution fails with a StackOverflowError **at the point where re-resolution of X would be required**.

~~This rule allows some leeway in the sequencing of the error check: the implementation may resolve some of the static arguments of Y, or may not.~~

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Note that an implementation is free to try to re-resolve X multiple times and keep looping until the stack actually overflows—once you've reached the nested X the first time, all further computation is not observable by users.

—Dan