Prototype type-specialization with temps and integer types

[maximecb]

The simplest thing to do, to start playing with type-specialization, would be to propagate types within blocks, but stop at branch instructions.

This will require modifying the context struct ctx_t to have somewhere to store local variable types.

We can start by propagating integer types and constants between instructions like putobject_INT2FIX_1_, opt_plus, opt_minus, etc. A good candidate benchmark to test such optimizations is optcarrot. We might also be able to eliminate multiple redundant array type checks.

[maximecb]

We can use the ruby_value_type enum from ruby/value_type.h. It even contains a T_NONE definition which we can use to keep track of when we don't know the type of something.

With regard to temporaries, it would make sense to map an array of types from the base of the stack, to avoid shifting values when pushing/popping.

We can add a type parameter to our stack push method, and a method to request the type of the topmost element on the stack. This should be enough to begin prototyping.

[maximecb]

I got the small prototype working :)

283bd8a