buffer.length performance regressed in 6.5.0

[Nibbler999]

• Version: v6.7.0
• Platform: Linux x86_64
• Subsystem: Buffer

[nibbler@nibbler ~]$ cat buffer.js 
'use strict';

var data = new Buffer(1024);

console.time('test');

for (var i = 0; i < 1000000; i++) {
    for (var j = 0; j < data.length; j++) {

    }
}

console.timeEnd('test');

[nibbler@nibbler ~]$ ~/Downloads/node-v6.4.0-linux-x64/bin/node buffer.js 
test: 623.471ms
[nibbler@nibbler ~]$ ~/Downloads/node-v6.5.0-linux-x64/bin/node buffer.js 
test: 2837.938ms

[mscdex]

I think about the only change that would have affected that was the V8 5.0->5.1 upgrade.

EDIT: FWIW v6.4.0 and master have the same results, but I can confirm that v6.5.0 is a little over twice as slow when running that test.

[mscdex]

/cc @nodejs/v8 ?

[targos]

I think the fix would be v8/v8@3c927e0 but the diff is huge.

[jeisinger]

@bmeurer

[bmeurer]

Yeah, I guess it would be fixed by v8/v8@3c927e0.

[apapirovski]

ping @targos @bmeurer — do you know if this was ever addressed in v6.x?

[addaleax]

@apapirovski I can reproduce this using the latest v6.x release (6.11.4), so I’d assume “no”. It might be something we’d just have to accept as a wontfix if nobody thinks they can put in the work to fix it?