Re: Correct line/column numbers in byte compiler messages

[Andrea Corallo <akrl@sdf.org>]

Have to apologize this is probably the quarantine effect but I couldn't
resist testing this:

#+BEGIN_SRC lisp
;; -*- lexical-binding: t; -*-
(require 'cl-lib)
(defvar elb-list (cl-loop for i from 0 to 1500000
                          if (cl-oddp i)
                          collect 'a
                          else
                          collect 'b))

(defun elb-eq ()
  (let ((n 0))
    (dolist (l elb-list n)
      (when (eq 'b l)
        (cl-incf n)))))

(defun elb-eq-entry ()
  (dotimes (_ 1000)
    (elb-eq)))
#+END_SRC

Results:

b619777dd6 (baseline) 50.09s
accurate-warning-pos  51.28s

This is about 2% perf penalty.

Interestingly with the __builtin_expect trick applied exec time gets
back to 50.65s.

We could probably find a benchmark that better highlights the difference
(this is potentially dominated by cache misses while pointer chasing the
list) but is it worth?

Regards

  Andrea

--
akrl@sdf.org