ptalk > August 2007

Advice for the OpenLaszlo optimizer

Since the OpenLaszlo compiler does not do common-subexpression elimination, when you are trying to optimize things, pretend you are writing in 1985 C. Instead of:

if (d.c[d.f]) d.c[d.f]( sd )

say:

var f = d.c[d.f];
if (f) f(sd);

Even better, when you find yourself having to write a null check, ask yourself if it would be cleaner, simpler, and more efficient to have the variable you are referencing not be nullable. For instance, if a variable is an array, consider using an empty array for its initial value, rather than null. This is a time/space trade-off: if there are many operations on the array and the variable is almost always not null, it will be more efficient to use an empty array; if there are few operations and the variable is usually null, then not allocating the empty array is the better choice.

(In Javascript 2, you will have the option of declaring a variable to be of a particular type, and you will have the option of declaring whether or not that variable can also be null. If you declare it not to be nullable, then the compiler will give you a compile-time warning if it cannot prove that the variable is never null, and it will insert the appropriate runtime check for you.

// This can be null, you have to check before using
var uplinkArray: Array;

// This cannot be null, you have to give a valid initial value
var uplinkArray: Array! = new Array();

Even though we don’t yet support the type declarations, we can follow the pattern and be ready…)