elisp: Compilation Tips
D.4 Tips for Making Compiled Code Fast
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Here are ways of improving the execution speed of byte-compiled Lisp
programs.
• Profile your program, to find out where the time is being spent.
Profiling.
• Use iteration rather than recursion whenever possible. Function
calls are slow in Emacs Lisp even when a compiled function is
calling another compiled function.
• Using the primitive list-searching functions ‘memq’, ‘member’,
‘assq’, or ‘assoc’ is even faster than explicit iteration. It can
be worth rearranging a data structure so that one of these
primitive search functions can be used.
• Certain built-in functions are handled specially in byte-compiled
code, avoiding the need for an ordinary function call. It is a
good idea to use these functions rather than alternatives. To see
whether a function is handled specially by the compiler, examine
its ‘byte-compile’ property. If the property is non-‘nil’, then
the function is handled specially.
For example, the following input will show you that ‘aref’ is
compiled specially (Array Functions):
(get 'aref 'byte-compile)
⇒ byte-compile-two-args
Note that in this case (and many others), you must first load the
‘bytecomp’ library, which defines the ‘byte-compile’ property.
• If calling a small function accounts for a substantial part of your
program’s running time, make the function inline. This eliminates
the function call overhead. Since making a function inline reduces
the flexibility of changing the program, don’t do it unless it
gives a noticeable speedup in something slow enough that users care
about the speed. Inline Functions.
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elisp: Programming Tips
elisp: Tips
elisp: Warning Tips