At http://dev.clojure.org/jira/browse/CLJS-1574 I added a smaller reproducible 
case that is pure JS. Basically all you need to do is use triple-equal with 
mixed types. The first non-string compare will cause subsequent string compares 
to be slow. If you use == instead there is no slowdown. Clearly a chrome/v8 
issue.

This code isn't hot, so it's not related to the higher-tier optimizing JITs.

On Tuesday, February 16, 2016 at 7:58:51 PM UTC-6, Stephen Nelson wrote:
> I've had an interesting day debugging a very strange performance problem in 
> Google Chrome.
> 
> http://dev.clojure.org/jira/browse/CLJS-1574
> 
> ``
> > (test)
> cljs equiv:  0.005 seconds
> > (= :added :ns)
> false
> > (test)
> cljs equiv:  1.517 seconds
> ```
> 
> I've never heard of equality causing side-effects before. My suspicion is a 
> Chrome JIT bug. Has anyone seen anything like this?

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