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Reader performance regression

From: Ludovic Courtès
Subject: Reader performance regression
Date: Sun, 31 Jan 2010 02:01:52 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)


A profile of ‘(compile-file "boot-9.scm")’ shows this:

  %     cumulative   self             
  time   seconds     seconds      name
   48.15      0.91      0.91  read
    8.15      0.15      0.15  #{\search-vector-rib\\\ 1944}#
    6.67      0.13      0.13  make-struct-layout
    5.93      1.88      0.11  eval

IOW, ‘read’ performs badly.

Commit 889975e51accb80491af76fc5db980aeb3edd342 may have been a
performance regression as it did away with the optimization that
consisted in using stack-allocated buffers in the common case, rather
than heap-allocated temporaries [0, 1].  (Indeed, Guile-Reader, whose
code is close to that of the pre-Unicode ‘scm_read ()’, is 1.4x faster
than current ‘read’.)

Mike: would you like to try to reintroduce that optimization?  :-)
What do you think?


[0] Commit 7337d56d5714227865aeca2b40b6bd97cce296d2 (2007-07-22).

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