From: "drbrain (Eric Hodel)" <drbrain@...7.net>
Date: 2013-11-16T09:47:11+09:00
Subject: [ruby-core:58372] [ruby-trunk - Bug #9114]	InstructionSequence.compile w/tailcall_optimization: true,	trace_instruction: false not working as expected


Issue #9114 has been updated by drbrain (Eric Hodel).


=begin
Here's an update where a call is in tail position, but from the output you'll see only the initial call uses the tail call optimization.

  source = <<-SOURCE
  def fact n, acc = 1
    if n.zero?
      acc
    else
      fact n - 1, acc * n
    end
  end
  
  fact 10000
  SOURCE
  
  i_seq = RubyVM::InstructionSequence.new source, nil, nil, nil,
    tailcall_optimization: false
  
  puts i_seq.disasm
  
  begin
    value = i_seq.eval
  
    p value
  rescue SystemStackError => e
    puts e
  end
  
  i_seq = RubyVM::InstructionSequence.new source, nil, nil, nil,
    tailcall_optimization: true
  
  puts i_seq.disasm
  
  begin
    value = i_seq.eval
  
    p value
  rescue SystemStackError => e
    puts e
  end
  
=end
----------------------------------------
Bug #9114: InstructionSequence.compile w/tailcall_optimization: true, trace_instruction: false not working as expected
https://bugs.ruby-lang.org/issues/9114#change-42971

Author: garysweaver (Gary Weaver)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin11.4.2]
Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN


Code to reproduce is a recursive sort I wrote; I was trying to compile RubyVM::InstructionSequence with tailcall_optimization: true, trace_instruction: false, which has worked before, but not for this case. 

method_string = <<RUBY
def recursively_sort(obj, in_sort_by=false)
 if obj.respond_to?(:sort_by)
   obj.sort_by{|*args|args.map{|v|recursively_sort(v, true)}}
 end rescue nil
 in_sort_by ? (obj.to_s rescue obj.inspect rescue nil) : obj
end
RUBY

RubyVM::InstructionSequence.new(method_string, nil, nil, nil, tailcall_optimization: true, trace_instruction: false).eval

a = eval '[{b:['*1000 + '2,1' + '],a:1}]'*1000

recursively_sort a

results in error for latest releases of Ruby 1.9.3 and 2.0.0:

1.9.3-p448 :014 >   recursively_sort a
SystemStackError: stack level too deep
	from /Users/gary/.rvm/rubies/ruby-1.9.3-p448/lib/ruby/1.9.1/irb/workspace.rb:80
Maybe IRB bug!

2.0.0p247 :014 >   recursively_sort a
SystemStackError: stack level too deep
	from /Users/gary/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/irb/workspace.rb:86
Maybe IRB bug!

I had assumed that since the blocks were defined within the tail call optimized method that referenced the method compiled with TCO, it would still be tail call optimized.

Did I do something wrong/is there a suggested workaround?

Thanks for looking at this!


-- 
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