It seems that OP_JMPUW does not call the ensure block when a is pointing to the beginning of the begin block.

For example:

for _ in [1]
  begin
    puts 1
    redo
  ensure
    puts 2
    break
  end
end

Ruby 3.3 will print:

1
2
=> nil

mruby (master) is indefinitly printing 1.

This probably happens because OP_JMPUW is pointing to puts 1, so it interprets it as jumping before puts 1 and after the begin keyword. However, it should jump before puts 1 to outside of the begin block and call the ensure block.

https://github.com/mruby/mruby/blob/3505874f72fb6e7f78cba6f3d7cf9d587349667c/src/vm.c#L1724C11-L1724C109

If I understand correctly, the condition should be changed from:

a < mrb_irep_catch_handler_unpack(ch->begin)

to:

a <= mrb_irep_catch_handler_unpack(ch->begin)