🚀 go-pugleaf

In article <561@etive.ed.ac.uk> db@lfcs.ed.ac.uk (Dave Berry) writes:

|Would it be sensible to optimise the following code:

|a := function ();
|b := (complicated expression) * a;

|to the equivalent of:

|a:= function ();
|if (a == 0)
|  b := 0;
|else
|  (complicated expression) * a;


|Assuming:
|  the result returned by "function" is a very small integer (including 0),
|	and isn't known at compile-time
|  "complicated_expression" has no side-effects and would take much longer
|	to evaluate than a comparison with 0.
|  the time taken to compile a program isn't considered.

This is not a good optimization, unless the compiler can determine at compile
time that 'a' is much more likely to be 0 than not.  Since this is very
difficult to determine at compile time, it is usually not done.

Note:  if you know that 'a' is going to be 0 most of the time it might pay to
recode your first example into your second example.  But you have to make the
choice, not the compiler, since this involves information that is not
(usually) known to the compiler.
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