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Bug #3841

Updated by ko1 (Koichi Sasada) about 2 years ago

=begin
I have been playing with the concept of caching compiled Ruby instruction sequences and reloading them later. For now the simplest way to do it is to use RubyVM::InstructionSequence.to_a() and Marshal.dump() to convert the resulting array to a smaller binary byte sequence. While testing this, I found that some Ruby scripts worked fine when an instruction sequence was reloaded, but others broke.

As a test, I decided to try compiling irb.rb and its dependencies. When I try to reload the compiled sequences, the first file that breaks is irb/extend-command.rb. I tracked it down to the way "for <vars> in <list>" code block and parameters are handled, but I am not sure how to fix it. When I converted each "for <vars> in <list>" loop to "<list>.each {|<vars>|", it started working perfectly. Here's an example of how the disassembly differs between the two loops:


```


def self.install_extend_commands
@EXTEND_COMMANDS.each {|args|
def_extend_command(*args)
}
end
== disasm: <RubyVM::InstructionSequence:block in install_extend_commands@irb/extend-command.rb>
== catch table
| catch type: redo st: 0000 ed: 0012 sp: 0000 cont: 0000
| catch type: next st: 0000 ed: 0012 sp: 0000 cont: 0012
|------------------------------------------------------------------------
local table (size: 2, argc: 1 [opts: 0, rest: -1, post: 0, block: -1] s3)
[ 2] args<Arg>
0000 trace 1 ( 110)
0002 putnil
0003 getdynamic args, 0
0006 send :def_extend_command, 1, nil, 10, <ic:0>
0012 leave

def self.install_extend_commands
for args in @EXTEND_COMMANDS
def_extend_command(*args)
end
end
== disasm: <RubyVM::InstructionSequence:block in install_extend_commands@irb/extend-command.rb>
== catch table
| catch type: redo st: 0005 ed: 0016 sp: 0000 cont: 0005
| catch type: next st: 0005 ed: 0016 sp: 0000 cont: 0016
|------------------------------------------------------------------------
local table (size: 2, argc: 1 [opts: 0, rest: -1, post: 0, block: -1] s3)
[ 2] ?<Arg>
0000 getdynamic *, 0 ( 206)
0003 setlocal args ( 204)
0005 trace 1 ( 205)
0007 putnil
0008 getlocal args
0010 send :def_extend_command, 1, nil, 10, <ic:0>
0016 leave
```



In this example, rb_id2name() returns NULL for the name of the argument passed to the code block. That is why it puts a "?" in the local table and a "*" in the getdynamic command. The to_a() method has a similar problem, and it appears to put a number there instead. When I use the load() method to convert the array back into an instruction sequence and try to execute it, the code block ends up receiving a number as a parameter instead of the entry in the list it is supposed to get.

I imagine this is not a high priority for the Ruby core team, and I don't mind putting in some work to fix it. However, it looks like it would take me a while to figure out, so I would appreciate any tips you could give me to point me in the right direction.

Thank you,
Sean O'Neil
=end

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