swift234

teach AllocBoxToStack to remove alloc_stack's that are artificial (or inlined)
and only stored to.  With this change, we now -emit-sil this testcase:

func f() {
 var a = 1
}

as:

sil @_T1t1fFT_T_ : $@thin () -> () {
bb0:
  %0 = tuple ()
  %1 = alloc_stack $Int64  // var a               // users: %8, %7
  %2 = metatype $Int64.metatype
  %3 = metatype $Int64.metatype
  %4 = module #Builtin
  %5 = integer_literal $Builtin.Int64, 1          // user: %6
  %6 = struct $Int64 (%5 : $Builtin.Int64)        // user: %7
  store %6 to %1#1 : $*Int64
  dealloc_stack %1#0 : $*@local_storage Int64
  %9 = tuple ()                                   // user: %10
  return %9 : $()
}



Swift SVN r9305