module RubyVM::YJIT

This module allows for introspection of YJIT, CRuby’s in-process just-in-time compiler. This module exists only to help develop YJIT, as such, everything in the module is highly implementation specific and comes with no API stability guarantee whatsoever.

This module may not exist if YJIT does not support the particular platform for which CRuby is built. There is also no API stability guarantee as to in what situations this module is defined.

Public Class Methods

code_gc() click to toggle source

Free and recompile all existing JIT code

# File ruby_3_2_4/yjit.rb, line 209
def self.code_gc
disasm(iseq) click to toggle source

Produce disassembly for an iseq

# File ruby_3_2_4/yjit.rb, line 183
def self.disasm(iseq)
  # If a method or proc is passed in, get its iseq
  iseq = RubyVM::InstructionSequence.of(iseq)

  if self.enabled?
    # Produce the disassembly string
    # Include the YARV iseq disasm in the string for additional context
    iseq.disasm + "\n" + Primitive.rb_yjit_disasm_iseq(iseq)
dump_exit_locations(filename) click to toggle source

Marshal dumps exit locations to the given filename.


If ‘–yjit-exit-locations` is passed, a file named “yjit_exit_locations.dump” will automatically be generated.

If you want to collect traces manually, call ‘dump_exit_locations` directly.

Note that calling this in a script will generate stats after the dump is created, so the stats data may include exits from the dump itself.

In a script call:

at_exit do

Then run the file with the following options:

ruby --yjit --yjit-trace-exits test.rb

Once the code is done running, use Stackprof to read the dump file. See Stackprof documentation for options.

# File ruby_3_2_4/yjit.rb, line 138
def self.dump_exit_locations(filename)
  unless trace_exit_locations_enabled?
    raise ArgumentError, "--yjit-trace-exits must be enabled to use dump_exit_locations."

  File.binwrite(filename, Marshal.dump(RubyVM::YJIT.exit_locations))
enabled?() click to toggle source

Check if YJIT is enabled

# File ruby_3_2_4/yjit.rb, line 13
def self.enabled?
  Primitive.cexpr! 'RBOOL(rb_yjit_enabled_p())'
exit_locations() click to toggle source

If –yjit-trace-exits is enabled parse the hashes from Primitive.rb_yjit_get_exit_locations into a format readable by Stackprof. This will allow us to find the exact location of a side exit in YJIT based on the instruction that is exiting.

# File ruby_3_2_4/yjit.rb, line 36
def self.exit_locations
  return unless trace_exit_locations_enabled?

  results = Primitive.rb_yjit_get_exit_locations
  raw_samples = results[:raw].dup
  line_samples = results[:lines].dup
  frames = results[:frames].dup
  samples_count = 0

  # Loop through the instructions and set the frame hash with the data.
  # We use nonexistent.def for the file name, otherwise insns.def will be displayed
  # and that information isn't useful in this context.
  RubyVM::INSTRUCTION_NAMES.each_with_index do |name, frame_id|
    frame_hash = { samples: 0, total_samples: 0, edges: {}, name: name, file: "nonexistent.def", line: nil, lines: {} }
    results[:frames][frame_id] = frame_hash
    frames[frame_id] = frame_hash

  # Loop through the raw_samples and build the hashes for StackProf.
  # The loop is based off an example in the StackProf documentation and therefore
  # this functionality can only work with that library.
  # Raw Samples:
  # [ length, frame1, frame2, frameN, ..., instruction, count
  # Line Samples
  # [ length, line_1, line_2, line_n, ..., dummy value, count
  i = 0
  while i < raw_samples.length
    stack_length = raw_samples[i] + 1
    i += 1 # consume the stack length

    prev_frame_id = nil
    stack_length.times do |idx|
      idx += i
      frame_id = raw_samples[idx]

      if prev_frame_id
        prev_frame = frames[prev_frame_id]
        prev_frame[:edges][frame_id] ||= 0
        prev_frame[:edges][frame_id] += 1

      frame_info = frames[frame_id]
      frame_info[:total_samples] += 1

      frame_info[:lines][line_samples[idx]] ||= [0, 0]
      frame_info[:lines][line_samples[idx]][0] += 1

      prev_frame_id = frame_id

    i += stack_length # consume the stack

    top_frame_id = prev_frame_id
    top_frame_line = 1

    sample_count = raw_samples[i]

    frames[top_frame_id][:samples] += sample_count
    frames[top_frame_id][:lines] ||= {}
    frames[top_frame_id][:lines][top_frame_line] ||= [0, 0]
    frames[top_frame_id][:lines][top_frame_line][1] += sample_count

    samples_count += sample_count
    i += 1

  results[:samples] = samples_count
  # Set missed_samples and gc_samples to 0 as their values
  # don't matter to us in this context.
  results[:missed_samples] = 0
  results[:gc_samples] = 0
insns_compiled(iseq) click to toggle source

Produce a list of instructions compiled by YJIT for an iseq

# File ruby_3_2_4/yjit.rb, line 197
def self.insns_compiled(iseq)
  # If a method or proc is passed in, get its iseq
  iseq = RubyVM::InstructionSequence.of(iseq)

  if self.enabled?
reset_stats!() click to toggle source

Discard statistics collected for –yjit-stats.

# File ruby_3_2_4/yjit.rb, line 28
def self.reset_stats!
runtime_stats() click to toggle source

Return a hash for statistics generated for the –yjit-stats command line option. Return nil when option is not passed or unavailable.

# File ruby_3_2_4/yjit.rb, line 148
def self.runtime_stats
  stats = Primitive.rb_yjit_get_stats
  return stats if stats.nil?

  stats[:object_shape_count] = Primitive.object_shape_count
  return stats unless Primitive.rb_yjit_stats_enabled_p

  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

  # This only available on yjit stats builds
  if stats.key?(:vm_insns_count)
    # 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
    stats[:total_insns_count] = total_insns_count
    stats[:ratio_in_yjit] = yjit_ratio_pct

  # Make those stats available in RubyVM::YJIT.runtime_stats as well
  stats[:side_exit_count]  = side_exits
  stats[:total_exit_count] = total_exits
  stats[:avg_len_in_yjit]  = avg_len_in_yjit

stats_enabled?() click to toggle source

Check if –yjit-stats is used.

# File ruby_3_2_4/yjit.rb, line 18
def self.stats_enabled?
trace_exit_locations_enabled?() click to toggle source

Check if rb_yjit_trace_exit_locations_enabled_p is enabled.

# File ruby_3_2_4/yjit.rb, line 23
def self.trace_exit_locations_enabled?