Comment #10 on issue 505 by [email protected]: Implement function
denesting optimization
http://code.google.com/p/v8/issues/detail?id=505
This blog post http://blog.trevnorris.com/2013/08/long-live-callbacks.html
has an example that I think *may* be what is being referenced here. The
last time this bug was touched was in 2009. Since the release of ES5,
strictness should make such a non-closure first-class function much more
viable. The example used in the blog, is:
var SB = require('buffer').SlowBuffer;
function runner(cb, arg) {
process.nextTick(function() {
cb(arg);
});
}
var iter = 2e4;
for (var i = 0; i < iter; i++) {
runner(function genPrimes(max) {
var primes = [];
var len = ((max / 8) >>> 0) + 1;
var sieve = new SB(len);
sieve.fill(0xff, 0, len);
var cntr, x, j;
for (cntr = 0, x = 2; x <= max; x++) {
if (sieve[(x / 8) >>> 0] & (1 << (x % 8))) {
primes[cntr++] = x;
for (j = 2 * x; j <= max; j += x) {
sieve[(j / 8) >>> 0] &= ~(1 << (j % 8));
}
}
}
return primes;
}, i);
}
The blog author concludes that moving the definition of `genPrimes(max)`
outside of the scope results in a 9x runtime improvement. This seems to me
to be a "gotcha". If strict-mode requests all variables to be predeclaired
then this would be an easy optimization that I imagine would be beneficial
in a lot of use cases.
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