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0 pointsgorhill12y ago0 comments

I thought that was an interesting comment, I did wonder originally if this could be something like that, but didn't follow up.

So now I took the time to try to go around this by rearranging the calls, and all of a sudden results make more sense:

http://jsperf.com/makekey-concat-vs-join/10

Results:

1. Firefox 29 makeKeyConcat / makeKeyConcatObj = ~440 Mops/s

2. Firefox 29 makeKeyCodepoint / makeKeyCodepointObj = ~64 Mops/s

3. Chrome 34 makeKeyCodepoint / makeKeyCodepointObj = ~5.7 Mops/s

4. Chrome 34 makeKeyConcat / makeKeyConcatObj = = ~2.2 Mops/s

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2 comments · 2 top-level

bzbarsky12y ago

For what it's worth, as far as I can tell SpiderMonkey is still more or less optimizing away the makeKeyConcat / makeKeyConcatObj testcases in Firefox 29, and all of them on trunk. I bet it's inlining the functions, discovering the arguments are constant strings and hence the return values are constant, constant-folding the if conditions, etc...

I tried to work around that in http://jsperf.com/makekey-concat-vs-join/11 but clearly that's not good enough.

Microbenchmarking a decent optimizing compiler is hard; it will typically be able to figure out that the ubench is pointless and optimize it all away...

tantalor12y ago

Cool! Now it looks like the object case is slightly slower, which is exactly what I'd expect.

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