Bug #12082: Tail-calling method can't catch exception raised by tail-called method

• Status: Closed
• Assignee: ko1 (Koichi Sasada)
• Target version: -
• Backport: 2.1: WONTFIX, 2.2: DONE, 2.3: DONE

[rhenium (Kazuki Yamaguchi)]

The following code doesn't work as expected, on all versions of Ruby with tail call optimization (1.9.1 to 2.3.0).

def do_raise
  raise "should be rescued"
end
options = {
  tailcall_optimization: true,
  trace_instruction: false,
}
RubyVM::InstructionSequence.compile(<<EOF, __FILE__, __FILE__, __LINE__, options).eval
  def test_rescue
    return do_raise
    1 + 2
  rescue
    :ok
  end
EOF

p test_rescue # should print :ok, but raises "should be rescued"

Looks like nop instruction is (also) used to avoid this optimization (compile.c), but when doing early return, no nop is inserted.

I attached a (dirty) fix for this. Maybe there is a cleaner way.

[ko1 (Koichi Sasada)]

• Assignee set to ko1 (Koichi Sasada)

[rhenium (Kazuki Yamaguchi)]

• File 0001-compile.c-don-t-do-tail-call-optimization-if-covered-v2.patch 0001-compile.c-don-t-do-tail-call-optimization-if-covered-v2.patch added

Updating my patch, because it breaks such code:

def errinfo
  $!
end
RubyVM::InstructionSequence.compile(<<EOF, __FILE__, __FILE__, __LINE__, tailcall_optimization: true).eval
  def test_rescue
    raise "a"
  rescue
    errinfo
  end
EOF

p test_rescue # should return a RuntimeError

[nobu (Nobuyoshi Nakada)]

https://github.com/ruby/ruby/compare/trunk...nobu:bug/12082-tailcall_inhibited_by_rescue?expand=1

[ko1 (Koichi Sasada)]

Thank you for reporting and patches.

Nobu's patch seems good. Could you commit it?

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset r54542.

---

compile.c: disable tco with rescue

• compile.c (iseq_optimize): disable tail call optimization in
  rescued, rescue, and ensure blocks.
  [ruby-core:73871] [Bug #12082]

[usa (Usaku NAKAMURA)]

• Backport changed from 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN to 2.1: WONTFIX, 2.2: REQUIRED, 2.3: REQUIRED

[usa (Usaku NAKAMURA)]

• Backport changed from 2.1: WONTFIX, 2.2: REQUIRED, 2.3: REQUIRED to 2.1: WONTFIX, 2.2: DONE, 2.3: REQUIRED

ruby_2_2 r54698 merged revision(s) 54542,54548.

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 2.1: WONTFIX, 2.2: DONE, 2.3: REQUIRED to 2.1: WONTFIX, 2.2: DONE, 2.3: DONE

ruby_2_3 r54715 merged revision(s) 54141,54542,54548.