use the return jump to jump to the return sequence

thus every method only has one exit
should make multi return messages smaller
especially when we have escape analisis
(maybe will help with inlining too)

lib/risc/callable_compiler.rb

@@ -13,14 +13,28 @@ module Risc
     def initialize( callable )
       @callable = callable
       @regs = []
-      @risc_instructions = Risc.label(source_name, source_name)
-      @risc_instructions << Risc.label( source_name, "unreachable")
+      init_instructions
       @current = @risc_instructions
       @constants = []
       @block_compilers = []
     end
     attr_reader :risc_instructions , :constants , :block_compilers , :callable
 
+    def init_instructions
+      @risc_instructions = Risc.label(source_name, source_name)
+      @risc_instructions.append Risc.label( source_name, "return_label")
+      @risc_instructions.append Mom::ReturnSequence.new.to_risc(self)
+      @risc_instructions.append Risc.label( source_name, "unreachable")
+      reset_regs
+    end
+
+    def return_label
+      @risc_instructions.each do |ins|
+        next unless ins.is_a?(Label)
+        return ins if ins.name == "return_label"
+      end
+    end
+
     # convert the given mom instruction to_risc and then add it (see add_code)
     # continue down the instruction chain unti depleted
     # (adding moves the insertion point so the whole mom chain is added as a risc chain)