Bug #9114
closedInstructionSequence.compile w/tailcall_optimization: true, trace_instruction: false not working as expected
Description
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!
Updated by garysweaver (Gary Weaver) over 8 years ago
btw- that method is incorrect, and when I wrote a better/working method, now it doesn't have that error in 2.0.0p247 but still fails with 1.9.3-p448. Not sure why:
method_string = <<RUBY
def recursively_sort(obj)
case obj
when Array
obj.map!{|v| recursively_sort(v)}.sort_by!{|v| (v.to_s rescue nil) }
when Hash
obj = Hash[Hash[obj.map{|k,v| [recursively_sort(k),recursively_sort(v)]}].sort_by{|k,v| [(k.to_s rescue nil), (v.to_s rescue nil)]}]
else
obj
end
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
So, there is something about the "bad" method in the original post that keeps TCO from working even in Ruby 2. Thanks.
Updated by drbrain (Eric Hodel) over 8 years ago
Which call is in tail position for this method? I'm not seeing it.
Updated by drbrain (Eric Hodel) over 8 years ago
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
Updated by drbrain (Eric Hodel) over 8 years ago
- Status changed from Open to Assigned
- Assignee set to ko1 (Koichi Sasada)
Updated by garysweaver (Gary Weaver) over 8 years ago
Eric,
My apologizes as I probably wasted your time with that. The problem with the code you posted is that for TCO you still have to specify trace_instruction: false. If you execute the following, it is fine in Ruby 2.0.0p247 at least, unless it doesn't work in core:
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: true, trace_instruction: false
puts i_seq.disasm
begin
value = i_seq.eval
p value
rescue SystemStackError => e
puts e
end
I wasn't doing a tail call, which was my problem I think :( , so can close.
Updated by drbrain (Eric Hodel) over 8 years ago
- Status changed from Assigned to Rejected
No time was wasted, I wanted to be sure your use-case was understood.
As you requested, this issue is now closed.