Bug 16595 – Add evaluateToVoid() and LoopNode subclasses which ignore completion type

• Component: JavaScriptCore
• Status: RESOLVED INVALID

[Eric Seidel (no email)]

Add evaluateToVoid() and LoopNode subclasses which ignore completion type

Loop nodes are spending time updating a completion value to be returned (and generally ignored).  For example, most for loops never have their returned completion type examined.  I've never seen code like this:

function bar() {
  for(var x = 0; x < 10; x++)
       x;
}

alert(bar());

Only in cases like that do we need to care what the loop completion value was.

In the common case, we can use a reverse execution walk through the node tree to keep track of when completion values are ignored:

var x = 2; // the fact that this updates the last completion value is completely ignored
var y = 4;

and use evaluateToVoid() calls instead.  We could even swap out entire BlockNodes which call void executeToVoid(exec) instead.

[Eric Seidel (no email)]

actually, the only way to access a completion value is from a function w/o a return value or an eval statement so you don't even need to walk, you just look at the last statement.  in the global context you can always evaluate to void

[Cameron Zwarich (cpst)]

This is now irrelevant after SquirrelFish.