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:

  • (Boolean) 


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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:

  • (Boolean) 


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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