rename allocator to standard_allocator

planning to have platform dish it out

lib/risc/standard_allocator.rb

@@ -0,0 +1,68 @@
+module Risc
+  #
+  # StandardAllocator keeps a list of registers whole names it accuires from the
+  # Plaform.
+  #
+  # It allocates registers by going throught the instructions and dishing
+  # out sequential registers.
+  # Before doing that it determines live ranges, so registers can be returned
+  # when not used anymore, and thus reused.
+  class StandardAllocator
+
+    def initialize( compiler , platform)
+      @compiler = compiler
+      @platform = platform
+      @used_regs = {}
+      reset_used_regs
+    end
+    attr_reader :used_regs , :compiler , :platform
+
+    def used_regs_empty?
+      @used_regs.empty?
+    end
+
+    def use_reg(reg)
+      raise "not reg #{reg.class}" unless reg.is_a?(RegisterValue)
+      @used_regs[reg.symbol] = reg
+    end
+
+    #
+    def release_reg(reg)
+      @used_regs.pop
+    end
+
+    def clear_used_regs
+      @used_regs.clear
+    end
+
+    #helper method to calculate with register symbols
+    def next_reg_use( type , extra = {} )
+      int = @symbol[1,3].to_i
+      raise "No more registers #{self}" if int > 11
+      sym = "r#{int + 1}".to_sym
+      RegisterValue.new( sym , type, extra)
+    end
+
+    def copy( reg , source )
+      copied = use_reg reg.type
+      add_code Register.transfer( source , reg , copied )
+      copied
+    end
+
+    # releasing a register (accuired by use_reg) makes it available for use again
+    # thus avoiding possibly using too many registers
+    def release_reg( reg )
+      reg = reg.symbol if reg.is_a?(RegisterValue)
+      raise "not symbol #{reg}:#{reg.class}" unless reg.is_a?(Symbol)
+      @used_regs.delete(reg)
+    end
+
+    # reset the registers to be used. Start at r4 for next usage.
+    # Every statement starts with this, meaning each statement may use all registers, but none
+    # get saved. Statements have affect on objects.
+    def reset_used_regs
+      @used_regs.clear
+    end
+
+  end
+end