From: "tekknolagi (Maxwell Bernstein) via ruby-core" <ruby-core@...>
Date: 2026-11-10T17:27:29+00:00
Subject: [ruby-core:127409] [Ruby Bug#22533] Peephole optimizer infinite loop

Issue #22533 has been reported by tekknolagi (Maxwell Bernstein).

----------------------------------------
Bug #22533: Peephole optimizer infinite loop
https://bugs.ruby-lang.org/issues/22533

* Author: tekknolagi (Maxwell Bernstein)
* Status: Open
* Target version: 4.0
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
The following code compiles a small loop with and without the peephole optimizer. It spawns a subprocess and waits 5 seconds before killing it to demonstrate the hang.

    SRC = "while true; if true then 1 end; end"
    pid = fork do
      RubyVM::InstructionSequence.compile(SRC)
      exit!(0)
    end
    deadline = Time.now + 5
    status = nil
    while Time.now < deadline
      break if (status = Process.waitpid2(pid, Process::WNOHANG))
      sleep 0.05
    end
    if status
      puts "compiled (#{status[1].inspect}): not reproduced"
    else
      Process.kill(:KILL, pid)
      Process.wait(pid)
      puts "compile_parsey(#{SRC.inspect}) still running after 5s: killed (hang)"
    end
    ok = RubyVM::InstructionSequence.compile(SRC, nil, nil, 1, peephole_optimization: false)
    puts "without the peephole pass it compiles: #{ok.to_a[13].size} body entries"

It also happens with `.compile_parsey`. This affects at least 3.4+ through master.



-- 
https://bugs.ruby-lang.org/
______________________________________________
 ruby-core mailing list -- ruby-core@ml.ruby-lang.org
 To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org
 ruby-core info -- https://ml.ruby-lang.org/mailman3/lists/ruby-core.ml.ruby-lang.org/