rename register to risc

seems to fit the layer much better as we really have a very reduced
instruction set

lib/risc/instructions/function_call.rb

@@ -0,0 +1,33 @@
+module Risc
+  # name says it all really
+  # only arg is the method object we want to call
+  # assembly takes care of the rest (ie getting the address)
+
+  class FunctionCall < Instruction
+    def initialize( source , method )
+      super(source)
+      @method = method
+    end
+    attr_reader :method
+
+    def to_s
+      "FunctionCall: #{method.name}"
+    end
+  end
+
+  def self.function_call( source , method )
+    Risc::FunctionCall.new( source , method )
+  end
+
+  def self.issue_call( compiler , callee )
+    return_label = Risc.label("_return_label #{callee.name}" , "#{compiler.type.object_class.name}.#{compiler.method.name}" )
+    ret_tmp = compiler.use_reg(:Label)
+    compiler.add_load_constant("#{callee.name} load ret", return_label , ret_tmp)
+    compiler.add_reg_to_slot("#{callee.name} store ret", ret_tmp , :new_message , :return_address)
+    compiler.add_transfer("#{callee.name} move new message", Risc.new_message_reg , Risc.message_reg )
+    compiler.add_code Risc.function_call( "#{callee.name} call" , callee )
+    compiler.add_code return_label
+    compiler.add_transfer("#{callee.name} remove new message", Risc.message_reg , Risc.new_message_reg )
+    compiler.add_slot_to_reg("#{callee.name} restore message" , :new_message , :caller , :message )
+  end
+end