calc sp

t.rb

source = %q{
  case 0
  in a: 0
  end
}

RubyVM::InstructionSequence.compile_option = RubyVM::InstructionSequence.compile_option.transform_values do |v|
  (v == true or v == false) ? false : v
end

iseq = RubyVM::InstructionSequence.compile(source)

sps = iseq.to_a[-1].filter_map do |i|
  case i
  in [:branchif | :branchunless | :branchnil | :pop | :leave | :setlocal | :checkmatch | :getconstant, *] 
    -1
  in [:nop | :swap | :jump | :checktype | :setn , *] 
    0
  in [x, *] if /putobject/ =~ x.to_s 
    1
  in [:putnil | :putspecialobject | :dup | :topn | :putself | :duparray | :duphash, *] 
    1
  in [:dupn, n]
    n
  in [:adjuststack, n]
    -n
  in [:newarray | :newhash, n]
    1 - n
  in [:opt_send_without_block | :send, {orig_argc:, kw_arg:}, *]
    1 - (1 + orig_argc + kw_arg.length)
  in [:opt_send_without_block | :send, {orig_argc:}, *]
    1 - (1 + orig_argc)
  in [*]
    raise "unknown insn: #{i.inspect}"
  in _
    nil
  end
end

sps = sps.inject([[0, 0]]) do |r, i|
  r << [i, r[-1][1] + i]
end
sps.shift

puts source
puts
iseq.disasm.each_line.drop_while {|i| !(/\A0000 / =~ i)}.zip(sps) do |l, (sp, sum)|
  print('%2d -> %2d (%2d)  %s' % [sum - sp, sum, sp, l])
end