GNU bug report logs - #21765
24.5; Profiler innefective for recursive functions

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Jonathan H <pythonnut <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.5; Profiler innefective for recursive functions
Date: Mon, 26 Oct 2015 10:47:01 -0700

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The Emacs profiler cannot be used to effectively profile, because the
reports do not flatten the recursion.

Take for example, this recipie:

;; Naive Fibonacci has terrible time complexity.
(defun fib (n)
  (if (< n 3)
      1
    (+ (fib (- n 1))
       (fib (- n 2)))))

(profiler-start 'cpu)
(fib 30)
(profiler-report)
(profiler-stop)

Here, The profiler report assigns (nearly) all of the time to (+ ...),
including time from deeper invocations of fib (and their invocations of (+
...), which makes the profiling report less-than-optimal.

Thanks,
PythonNut

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