Instrumentation into Block IR

[ChingLongTin]

Call implementation will be after the algorithms for instrumenting functions are completed.

1. allocating optionNme
   This changed some diff tests (OpenWildcard.mls, Imports.mls, ImportMLs.mls) that imported Option themselves.
   If I allocate optionNme after checking if stageCode is enabled, it fails to link to the file.
   Is there some way to avoid changing the diff tests, or is this fine?

2. implementing I-Inst
   The current shape for Class C(n:s) includes the field names (n), but the field names are not available in Instantiation.
   The field names are used in sel. If the class is staged using I-Cls, then we can use the staged ClsLikeDefn to retrieve the symbol names, but when do we do when it isn't staged?

class A(a)
staged module B
  class C(a)
  fun f() = 
    new C(1) // ok, C is staged
    new A(1) // not ok, we don't know field names of A after instrumentation

[NeilKleistGao]

So far, if we introduce things from #387, it will fail, since we do not consider the mutable features that #387 is using. We probably need to only handle classes inside modules and leave other things untouched.

[ChingLongTin]

I'm not sure how to bring the classes defined in the module to the next stage, The class C depends on the variable x defined within the module, so the let statement needs to be staged as well.
Will the classes never depend on variables that use mutable features?

module A with
  let x = 1
  fun get() = x
  class C() with
    fun get() = x
  fun add() =
    x = x + 1

[LPTK]

Mutation should probably not be allowed in staged modules, I think.

BTW, it should be set x = x + 1 or equivalently set x += 1. OTOH x = x + 1 is an only an initialization statement (and wll be rejected here once we have type checking).

[NeilKleistGao]

b1 should not be discarded. When we have an early-return, we should discard the rest of the body, i.e., b2.

[NeilKleistGao]

Notice that the default name of TempSymbol is always tmp, and those symbols will be renamed with a number suffix during codegen. We probably also need to use Scope to avoid name clashes here.