The current usefulness of turbolizer seems... mixed.
Turbofan generated code is highly variable. Changes in argument types and optimization order can result in very different code being emitted.
It's not like "all these cases were well optimized, but this one case wasn't, so let's fix/avoid that one". Instead, it's "well, that's a diverse mess of results, hmm...".
Perhaps that will change. One project objective is apparently optimization with fewer performance cliffs. But another objective is a compiler which better serves low-end mobile devices - thus raising the bar for what optimizations are worth spending time on. There's a tension between those two.
Also, CPU branch prediction makes interpreting the resulting assembly more interesting. Turbofan output has a lot of deopt guards. Tests that the assumptions used when writing the optimized code are still true. But say one bit of javascript optimizes to code with more guards than another. Do they matter? Maybe not, if the guards end up off mainline and hit cache.
So turbolizer seems helpful if you have a some red-hot performance chokepoint. But at present, perhaps less so for providing more general guidance.
Turbofan generated code is highly variable. Changes in argument types and optimization order can result in very different code being emitted.
It's not like "all these cases were well optimized, but this one case wasn't, so let's fix/avoid that one". Instead, it's "well, that's a diverse mess of results, hmm...".
Perhaps that will change. One project objective is apparently optimization with fewer performance cliffs. But another objective is a compiler which better serves low-end mobile devices - thus raising the bar for what optimizations are worth spending time on. There's a tension between those two.
Also, CPU branch prediction makes interpreting the resulting assembly more interesting. Turbofan output has a lot of deopt guards. Tests that the assumptions used when writing the optimized code are still true. But say one bit of javascript optimizes to code with more guards than another. Do they matter? Maybe not, if the guards end up off mainline and hit cache.
So turbolizer seems helpful if you have a some red-hot performance chokepoint. But at present, perhaps less so for providing more general guidance.