function call now saves the return address before calling

that means SaveReturn is obsolete (breaks loads of tests)
first step towards multi - return which obviously can not have the
callee save return address.
In fact this would make FunctionCall redundant too, as it is really
just a branch

lib/register/instruction.rb

@@ -123,7 +123,6 @@ require_relative "instructions/load_constant"
 require_relative "instructions/syscall"
 require_relative "instructions/function_call"
 require_relative "instructions/function_return"
-require_relative "instructions/save_return"
 require_relative "instructions/register_transfer"
 require_relative "instructions/label"
 require_relative "instructions/branch"

lib/register/instructions/function_call.rb

@@ -17,9 +17,14 @@ module Register
 
   def self.issue_call compiler , callee
     source = "_issue_call(#{callee.name})"
+    return_label = Label.new("_return_label" , "_return_label" )
+    ret_tmp = compiler.use_reg(:Label)
+    compiler.add_code Register::LoadConstant.new(source, return_label , ret_tmp)
+    compiler.add_code Register.set_slot(source, ret_tmp , :new_message , :return_address)
     # move the current new_message to message
     compiler.add_code RegisterTransfer.new(source, Register.new_message_reg , Register.message_reg )
     # do the register call
     compiler.add_code FunctionCall.new( source , callee )
+    compiler.add_code return_label
   end
 end

lib/register/instructions/save_return.rb

@@ -1,32 +0,0 @@
-module Register
-
-  # save the return address of a call
-  # register and index specify where the return address is stored
-
-  # This instruction exists mainly, so we don't have to hard-code where the machine stores the
-  # address. In arm that is a register, but intel may (?) push it, and who knows, what other machines do.
-
-  class SaveReturn < Instruction
-    def initialize source , register , index
-      super(source)
-      @register = register
-      @index = index
-    end
-    attr_reader :register , :index
-
-    def to_s
-      "SaveReturn: #{register} [#{index}]"
-    end
-
-  end
-
-  # Produce a SaveReturn instruction.
-  # From is a register or symbol that can be transformed to a register by resolve_to_register
-  # index resolves with resolve_index.
-  def self.save_return code, from , index
-    index = resolve_index( from , index)
-    from = resolve_to_register from
-    SaveReturn.new( code , from , index )
-  end
-
-end