hg: valhalla/valhalla/langtools: Add support for tracking 'any'-related opcodes

[Remi Forax]

On 07/28/2014 11:10 PM, John Rose wrote:
> On Jul 28, 2014, at 12:53 PM, Dan Smith <daniel.smith at oracle.com> wrote:
>
>> (Final note: it probably goes without saying, but there are other things besides bytecodes that need to be specialized, too, and eventually we'll want to come up with a comprehensive list of those things.)
> The 'J' and 'D' types are a pain point, since they require slot pairs.
>
> In the spirit of your 'nop' technique, I suggest allocating a slot-pair to each value of a specializable type.  Treat the extra slot, if unused, as padding or a nop.

yes, very good idea, so maxlocals will be always the same value for the 
specializable code and all the specialized versions.

I suppose that value types will not use several slots, otherwise if you 
change a value type to add a field,
you will need to recompile all codes that use that value type.
So either the interpreter will treat value type as objects or it will 
use a double indirection ?
(the stack will contains an index to a stack location inside the current 
stack frame containing all the values of the value type).

>
> In the case of method parameters you cannot preallocate padding, but it's simple to work around:  Copy the incoming parameter to a local slot-pair.
>
> The JIT will make that stuff go away, just like nops.
>
> — John

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