Class: Ruby2CExtension::Plugins::CaseOptimize

Inherits:
Ruby2CExtension::Plugin show all
Includes:
Tools::EnsureNodeTypeMixin
Defined in:
lib/ruby2cext/plugins/case_optimize.rb

Instance Attribute Summary

Attributes inherited from Ruby2CExtension::Plugin

#compiler

Instance Method Summary collapse

Methods included from Tools::EnsureNodeTypeMixin

#ensure_node_type

Methods inherited from Ruby2CExtension::Plugin

#global_c_code, #init_c_code

Constructor Details

#initialize(compiler) ⇒ CaseOptimize

Returns a new instance of CaseOptimize.



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# File 'lib/ruby2cext/plugins/case_optimize.rb', line 8

def initialize(compiler)
  super
  compiler.add_preprocessor(:case) { |cfun, node|
    handle_case(cfun, node.last) || node
  }
end

Instance Method Details

#fixed_immediate?(node) ⇒ Boolean

Returns:



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# File 'lib/ruby2cext/plugins/case_optimize.rb', line 19

def fixed_immediate?(node)
  # checks if the node is optimizable and if yes returns the equivalent C value
  if fixnum?(node)
    "LONG2FIX(#{node.last[:lit].inspect})"
  elsif Array === node
    case node.first
    when :nil
      "Qnil"
    when :true
      "Qtrue"
    when :false
      "Qfalse"
    else
      false
    end
  else
    false
  end
end

#fixnum?(node) ⇒ Boolean

Returns:



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# File 'lib/ruby2cext/plugins/case_optimize.rb', line 15

def fixnum?(node)
  Array === node && node.first == :lit && Fixnum === node.last[:lit]
end

#handle_case(cfun, hash) ⇒ Object 



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# File 'lib/ruby2cext/plugins/case_optimize.rb', line 39

def handle_case(cfun, hash)
  cur_when = hash[:body]
  fallback_whens = []
  opt_cases = []
  while cur_when.first == :when
    ensure_node_type(head = cur_when.last[:head], :array)
    cases = head.last.map { |wn| fixed_immediate?(wn) }
    break unless cases.all?
    case_c_code = cases.map { |c| "case #{c}:" }.join("\n")
    fixnum_whens = head.last.select { |wn| fixnum?(wn) }
    unless fixnum_whens.empty?
      goto_label = compiler.un("case_opt_label")
      case_c_code << "\n#{goto_label}:"
      fallback_whens << [:when, {
        :body => "Qnil;\ngoto #{goto_label}", # TODO: evil, depends on impl. details of comp_case/handle_when
        :head => [:array, fixnum_whens]
      }]
    end
    opt_cases << [case_c_code, cur_when.last[:body]]
    cur_when = cur_when.last[:next] || [:nil, {}]
  end
  return nil if opt_cases.empty? # nothing to optimize
  rest = cur_when
  if rest.first == :when # some whens are left construct a complete new case node
    rest = [:case, {:head => "case_opt_val", :body => rest}]
  end
  cfun.instance_eval {
    c_scope_res {
      l "VALUE case_opt_val;"
      l "case_opt_val = #{comp(hash[:head])};"
      l "switch (case_opt_val) {"
      opt_cases.each { |(case_code, body_node)|
        l case_code
        assign_res(comp(body_node))
        l "break;"
      }
      l "default:"
      if fallback_whens.empty?
        assign_res(comp(rest))
      else
        # link the fallback_whens
        fallback_whens.each_with_index { |wn, i|
          fallback_whens[i - 1].last[:next] = wn if i > 0
        }
        fallback_whens.last.last[:next] = "Qundef"
        c_if("!FIXNUM_P(case_opt_val)") {
          assign_res(comp_case({:head => "case_opt_val", :body => fallback_whens.first}))
        }
        c_else {
          assign_res("Qundef")
        }
        c_if("res == Qundef") {
          assign_res(comp(rest))
        }
      end
      l "}"
      "res"
    }
  }
end