swift234

delete the VarRefInst class and instruction - variable references
are now represented as uses of the lvalue that defines their location.

For example, we compile:

  var local_var : Int = 4
  var defaulted_var : Int
  return local_var + defaulted_var

into:

  %5 = alloc_var local_var, type=[byref(heap)] Int
  %6 = store %4 -> %5 [initialization]
  %7 = alloc_var defaulted_var, type=[byref(heap)] Int
  %8 = zerovalueinst Int
  %9 = store %8 -> %7 [initialization]
  %10 = constantref +, type=(lhs : Int64, rhs : Int64) -> Int64
*  %11 = load %5
*  %12 = load %7
  %13 = apply %10(%11, %12)
  %14 = return (%13)

The two *'d loads are loading the location of the two variables.  Some of
the sanity checking this change includes now causes us to die on uses of
arguments (whose locations we don't emit yet) and in foreach loops, which
aren't emitting their patterns yet.  Always more to do.



Swift SVN r2978