yjit.rb

# This module allows for introspection on YJIT, CRuby's experimental in-process
# just-in-time compiler. This module is for development purposes only;
# everything in this module is highly implementation specific and comes with no
# API stability guarantee whatsoever.
#
# This module is only defined when YJIT has support for the particular platform
# on which CRuby is built.
module RubyVM::YJIT
  if defined?(Disasm)
    def self.disasm(iseq, tty: $stdout && $stdout.tty?)
      iseq = RubyVM::InstructionSequence.of(iseq)

      blocks = blocks_for(iseq)
      return if blocks.empty?

      str = String.new
      str << iseq.disasm
      str << "\n"

      # Sort the blocks by increasing addresses
      sorted_blocks = blocks.sort_by(&:address)

      highlight = ->(str) {
        if tty
          "\x1b[1m#{str}\x1b[0m"
        else
          str
        end
      }

      cs = Disasm.new
      sorted_blocks.each_with_index do |block, i|
        str << "== BLOCK #{i+1}/#{blocks.length}: #{block.code.length} BYTES, ISEQ RANGE [#{block.iseq_start_index},#{block.iseq_end_index}) ".ljust(80, "=")
        str << "\n"

        comments = comments_for(block.address, block.address + block.code.length)
        comment_idx = 0
        cs.disasm(block.code, block.address).each do |i|
          while (comment = comments[comment_idx]) && comment.address <= i.address
            str << "  ; #{highlight.call(comment.comment)}\n"
            comment_idx += 1
          end

          str << sprintf(
            "  %<address>08x:  %<instruction>s\t%<details>s\n",
            address: i.address,
            instruction: i.mnemonic,
            details: i.op_str
          )
        end
      end

      block_sizes = blocks.map { |block| block.code.length }
      total_bytes = block_sizes.sum
      str << "\n"
      str << "Total code size: #{total_bytes} bytes"
      str << "\n"

      str
    end

    def self.comments_for(start_address, end_address)
      Primitive.comments_for(start_address, end_address)
    end

    def self.graphviz_for(iseq)
      iseq = RubyVM::InstructionSequence.of(iseq)
      cs = Disasm.new

      highlight = ->(comment) { "<b>#{comment}</b>" }
      linebreak = "<br align=\"left\"/>\n"

      buff = +''
      blocks = blocks_for(iseq).sort_by(&:id)
      buff << "digraph g {\n"

      # Write the iseq info as a legend
      buff << "  legend [shape=record fontsize=\"30\" fillcolor=\"lightgrey\" style=\"filled\"];\n"
      buff << "  legend [label=\"{ Instruction Disassembly For: | {#{iseq.base_label}@#{iseq.absolute_path}:#{iseq.first_lineno}}}\"];\n"

      # Subgraph contains disassembly
      buff << "  subgraph disasm {\n"
      buff << "  node [shape=record fontname=\"courier\"];\n"
      buff << "  edge [fontname=\"courier\" penwidth=3];\n"
      blocks.each do |block|
        disasm = disasm_block(cs, block, highlight)

        # convert newlines to breaks that graphviz understands
        disasm.gsub!(/\n/, linebreak)

        # strip leading whitespace
        disasm.gsub!(/^\s+/, '')

        buff << "b#{block.id} [label=<#{disasm}>];\n"
        buff << block.outgoing_ids.map { |id|
          next_block = blocks.bsearch { |nb| id <=> nb.id }
          if next_block.address == (block.address + block.code.length)
            "b#{block.id} -> b#{id}[label=\"Fall\"];"
          else
            "b#{block.id} -> b#{id}[label=\"Jump\" style=dashed];"
          end
        }.join("\n")
        buff << "\n"
      end
      buff << "  }"
      buff << "}"
      buff
    end

    def self.disasm_block(cs, block, highlight)
      comments = comments_for(block.address, block.address + block.code.length)
      comment_idx = 0
      str = +''
      cs.disasm(block.code, block.address).each do |i|
        while (comment = comments[comment_idx]) && comment.address <= i.address
          str << "  ; #{highlight.call(comment.comment)}\n"
          comment_idx += 1
        end

        str << sprintf(
          "  %<address>08x:  %<instruction>s\t%<details>s\n",
          address: i.address,
          instruction: i.mnemonic,
          details: i.op_str
        )
      end
      str
    end
  end

  # Return a hash for statistics generated for the --yjit-stats command line option.
  # Return nil when option is not passed or unavailable.
  def self.runtime_stats
    # defined in yjit_iface.c
    Primitive.get_yjit_stats
  end

  # Discard statistics collected for --yjit-stats.
  def self.reset_stats!
    # defined in yjit_iface.c
    Primitive.reset_stats_bang
  end

  def self.stats_enabled?
    Primitive.yjit_stats_enabled_p
  end

  def self.enabled?
    Primitive.cexpr! 'rb_yjit_enabled_p() ? Qtrue : Qfalse'
  end

  # Avoid calling a method here to not interfere with compilation tests
  if Primitive.yjit_stats_enabled_p
    at_exit { _print_stats }
  end

  class << self
    private

    # Format and print out counters
    def _print_stats
      stats = runtime_stats
      return unless stats

      $stderr.puts("***YJIT: Printing YJIT statistics on exit***")

      print_counters(stats, prefix: 'send_', prompt: 'method call exit reasons: ')
      print_counters(stats, prefix: 'invokesuper_', prompt: 'invokesuper exit reasons: ')
      print_counters(stats, prefix: 'leave_', prompt: 'leave exit reasons: ')
      print_counters(stats, prefix: 'gbpp_', prompt: 'getblockparamproxy exit reasons: ')
      print_counters(stats, prefix: 'getivar_', prompt: 'getinstancevariable exit reasons:')
      print_counters(stats, prefix: 'setivar_', prompt: 'setinstancevariable exit reasons:')
      print_counters(stats, prefix: 'oaref_', prompt: 'opt_aref exit reasons: ')
      print_counters(stats, prefix: 'expandarray_', prompt: 'expandarray exit reasons: ')
      print_counters(stats, prefix: 'opt_getinlinecache_', prompt: 'opt_getinlinecache exit reasons: ')
      print_counters(stats, prefix: 'invalidate_', prompt: 'invalidation reasons: ')

      side_exits = total_exit_count(stats)
      total_exits = side_exits + stats[:leave_interp_return]

      # Number of instructions that finish executing in YJIT.
      # See :count-placement: about the subtraction.
      retired_in_yjit = stats[:exec_instruction] - side_exits

      # Average length of instruction sequences executed by YJIT
      avg_len_in_yjit = retired_in_yjit.to_f / total_exits

      # Proportion of instructions that retire in YJIT
      total_insns_count = retired_in_yjit + stats[:vm_insns_count]
      yjit_ratio_pct = 100.0 * retired_in_yjit.to_f / total_insns_count

      $stderr.puts "bindings_allocations:  " + ("%10d" % stats[:binding_allocations])
      $stderr.puts "bindings_set:          " + ("%10d" % stats[:binding_set])
      $stderr.puts "compiled_iseq_count:   " + ("%10d" % stats[:compiled_iseq_count])
      $stderr.puts "compiled_block_count:  " + ("%10d" % stats[:compiled_block_count])
      $stderr.puts "invalidation_count:    " + ("%10d" % stats[:invalidation_count])
      $stderr.puts "constant_state_bumps:  " + ("%10d" % stats[:constant_state_bumps])
      $stderr.puts "inline_code_size:      " + ("%10d" % stats[:inline_code_size])
      $stderr.puts "outlined_code_size:    " + ("%10d" % stats[:outlined_code_size])

      $stderr.puts "total_exit_count:      " + ("%10d" % total_exits)
      $stderr.puts "total_insns_count:     " + ("%10d" % total_insns_count)
      $stderr.puts "vm_insns_count:        " + ("%10d" % stats[:vm_insns_count])
      $stderr.puts "yjit_insns_count:      " + ("%10d" % stats[:exec_instruction])
      $stderr.puts "ratio_in_yjit:         " + ("%9.1f" % yjit_ratio_pct) + "%"
      $stderr.puts "avg_len_in_yjit:       " + ("%10.1f" % avg_len_in_yjit)

      print_sorted_exit_counts(stats, prefix: "exit_")
    end

    def print_sorted_exit_counts(stats, prefix:, how_many: 20, left_pad: 4)
      exits = []
      stats.each do |k, v|
        if k.start_with?(prefix)
          exits.push [k.to_s.delete_prefix(prefix), v]
        end
      end

      exits = exits.sort_by { |name, count| -count }[0...how_many]
      total_exits = total_exit_count(stats)

      top_n_total = exits.map { |name, count| count }.sum
      top_n_exit_pct = 100.0 * top_n_total / total_exits

      $stderr.puts "Top-#{how_many} most frequent exit ops (#{"%.1f" % top_n_exit_pct}% of exits):"

      longest_insn_name_len = exits.map { |name, count| name.length }.max
      exits.each do |name, count|
        padding = longest_insn_name_len + left_pad
        padded_name = "%#{padding}s" % name
        padded_count = "%10d" % count
        percent = 100.0 * count / total_exits
        formatted_percent = "%.1f" % percent
        $stderr.puts("#{padded_name}: #{padded_count} (#{formatted_percent}%)" )
      end
    end

    def total_exit_count(stats, prefix: "exit_")
      total = 0
      stats.each do |k,v|
        total += v if k.start_with?(prefix)
      end
      total
    end

    def print_counters(counters, prefix:, prompt:)
      $stderr.puts(prompt)
      counters = counters.filter { |key, _| key.start_with?(prefix) }
      counters.filter! { |_, value| value != 0 }
      counters.transform_keys! { |key| key.to_s.delete_prefix(prefix) }

      if counters.empty?
        $stderr.puts("    (all relevant counters are zero)")
        return
      end

      counters = counters.to_a
      counters.sort_by! { |(_, counter_value)| counter_value }
      longest_name_length = counters.max_by { |(name, _)| name.length }.first.length
      total = counters.sum { |(_, counter_value)| counter_value }

      counters.reverse_each do |(name, value)|
        percentage = value.fdiv(total) * 100
        $stderr.printf("    %*s %10d (%4.1f%%)\n", longest_name_length, name, value, percentage);
      end
    end
  end
end