Project

General

Profile

Actions

Bug #15303

closed

Return tracepoint doesn't fire when tailcall optimization is applied

Added by alanwu (Alan Wu) over 5 years ago. Updated almost 5 years ago.

Status:
Closed
Assignee:
-
Target version:
-
ruby -v:
ruby 2.6.0dev (2018-11-14 trunk 65727) [x86_64-darwin17]
[ruby-core:89797]

Description

After a tailcall, the "return" tracepoint event is only fired once. Normally, after a call at the end of a method, the return event is fired twice, once for the callee returning and once for the caller returning.
The following script outputs

:call
:call
:call
:return
method_source = <<-RB
def toy(n)
   return if n == 2
   toy(n+1)
end
RB

iseq = RubyVM::InstructionSequence.compile(method_source, tailcall_optimization: true)
#puts iseq.disasm
iseq.eval

trace = TracePoint.new(:call, :return) do |tp|
    p tp.event
end

trace.enable
toy(0)

The "return" event behaves more like a "stack frame pop" event currently. I don't think it's feasible/desirable to have the same behavior when TCO is applied, but it would be nice if there was some way for the tracepoint to know a tail call is going to happen.
I'm raising this issue because the popular debugger "byebug" relies on these events to track execution in various stack frames. https://github.com/deivid-rodriguez/byebug/issues/481
Forwardable explicitly uses TCO which triggers this issue.


Files

no-tco-no-problem.patch (520 Bytes) no-tco-no-problem.patch alanwu (Alan Wu), 12/08/2018 05:27 AM

Related issues 1 (0 open1 closed)

Has duplicate Ruby master - Bug #15604: Backport r66349 to 2.5ClosedActions
Actions

Also available in: Atom PDF

Like0
Like0Like0Like0Like0Like0Like0Like0Like0Like0Like0Like0Like0Like0Like0Like0