jit_debauchery.rb

module BytecodeHelpers
  def g
    self
  end
  
  def puts_string string
    g.push_rubinius
    g.push_literal(string)
    g.send(:puts, 1, true)
    g.pop
  end
  
  def inspect_top
    g.dup_top
    g.push_rubinius
    g.swap
    g.send(:p, 1, true)
    g.pop
  end
end

class Demo
  dynamic_method(:jit_debauchery_check, "(snippet)") { |g|
    g.extend BytecodeHelpers
    
    done_label = g.new_label
    
    g.push_literal("a string")
      g.push_int("a string".size)
    g.send(:chr_at, 1) # This should ALWAYS be nil
    g.dup_top
    g.goto_if_nil(done_label) # This should ALWAYS goto
    
    # This code should NEVER be reached
    # If reached, it should raise PrimitiveFailure because the first arg is nil
    # instead of the expected string
    g.push_literal("abc")
      g.swap # The stack top is now our nil from before
      g.meta_push_0
    g.send(:find_string, 2)
    
    done_label.set!
    g.ret
    g.close
  }
end

demo = Demo.new

puts "Let's try it one time..."
demo.jit_debauchery_check
puts 'it "worked" (skipped the find_string call)!'
puts

puts "Let's try it a second time..."
demo.jit_debauchery_check
puts 'it "worked" (skipped the find_string call)!'
puts

puts "Let's try it many times until PrimitiveFailure is raised..."
while true
  demo.jit_debauchery_check
end