UserAgent: Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36

Steps to reproduce the problem:
1) With the following code:

var typed = new Uint32Array(250000);
var normal = Array.from(typed);         // Just to initialize array with zeroes

function NORMAL() {
    var start = performance.now();
    for (var i = 1, len = normal.length; i < len; ++i) normal[i] = i + normal[i-1];
    console.log("NORMAL: " + (performance.now() - start));
}

function TYPED() {
    var start = performance.now();
    for (var i = 1, len = typed.length; i < len; ++i) typed[i] = i + typed[i-1];
    console.log("TYPED: " + (performance.now() - start));
}

2) executions of TYPED() take up to 25 times SLOWER than executions of NORMAL(), specially after 3 or 4 executions

What is the expected behavior?
Executions of TYPED() should be faster, or at least not so much slower than NORMAL()

What went wrong?
My guess is that the optimizer is not working correctly with TypedArrays since v55

Did this work before? Yes version 54 was working OK, just days ago...

Chrome version: 55.0.2883.87  Channel: stable
OS Version: 6.3
Flash Version: Shockwave Flash 24.0 r0

I have a processing intensive app that deals with rendering images and audio in realtime. Its a vintage computer emulator.
http://webmsx.org

Since version 55 it runs approx. 6 times SLOWER then before.
The culprit seems to be TypedArrays. The same machine in v54 was running the emulation at nearly 900 fps, now it runs at 140 fps.

My code has a function that deals with TypedArrays. This function didn't even show in profiles before v55, and the parent function (the one who calls it) appeared in the profile with no more than 6% of the processing time.

Now the same function appears with about 56% of the processing time! No changes in my code.

The test case above is not really a good representation of my real scenario, but it also looks strange. Profiles of my app can be run and they will show the problem very clearly.

Something is really wrong and that makes Chrome run my project (and I guess other graphics and game-like apps) very poorly. Specially in slower devices like mobiles.

My guess is that some bug in the V8 optimization of TypedArrays was introduced in version 55.