Dbc
https://codereview.chromium.org/22545007/diff/20001/src/array.js
File src/array.js (right):
https://codereview.chromium.org/22545007/diff/20001/src/array.js#newcode1263
src/array.js:1263: if (!isProxy && %HasFastPackedElements(array) || i in
array) {
I don't think you can have indexed accessors while being packed. I think
we always go dictionary mode when accessors are installed. Holey arrays
would have this problem; but they are already excluded explicitly.
On 2013/08/13 15:47:16, Michael Starzinger wrote:
On 2013/08/13 14:10:22, Michael Starzinger wrote:
> It is _really_ surprising that the runtime call into
> Runtime_HasFastPackedElements is cheaper than the "in" keyword. This
suggests
> that there is a lot of potential in actually improving "in" in
general. This
> needs investigation of the generated code!
Now that I think about it, I don't actually think that this is a valid
optimization either. What happens if the callback actually changes the
array in
a way so that it remains in fast-packed mode, but "i" still runs out
of bounds.
Imagine the following callback.
var array = [1,2,3,4,5,6];
Object.defineProperty(array, '1', {
get: function () { array.length = 3; },
configurable: true
});
array.forEach(f);
https://codereview.chromium.org/22545007/
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