Created attachment 8368574 [details] prova.js The function maxHeapify calls the function left, that is a one-liner. If I remove the function call and substitute its code in its caller, the performance improves slightly. So I guess the function isn't inlined. I'm running this snippet in the IE console and in the Firefox console, and IE is a lot faster here (40 ms vs 600 ms).
Baseline is faster than Ion on this one (55ms vs 250ms without parallel compilation). Except maxHeapify being not inlined as it's recursive, I don't see anything particular Ion flags logs (no bailouts nor OSI).
The performance in the Developer Tools console is quite different than in normal web pages. Firefox is faster than IE and the function |left| is actually inlined.