From: "byroot (Jean Boussier) via ruby-core" <ruby-core@...>
Date: 2026-11-11T13:31:22+00:00
Subject: [ruby-core:127417] [Ruby Bug#22533] Peephole optimizer infinite loop

Issue #22533 has been updated by byroot (Jean Boussier).


I have a patch for this: https://github.com/ruby/ruby/pull/19844, but I'm not 100% certain it doesn't regress this optimization, and based on the handful of failing ZJIT tests, it looks like it does generate different code sometimes.

So I'd appreciate if someone with more knowledge of the peephole optimizer could review.

----------------------------------------
Bug #22533: Peephole optimizer infinite loop
https://bugs.ruby-lang.org/issues/22533#change-119863

* 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/