Quadrupling code performance with a "useless" if

lobsters comment points out [[unlikely]] works here for clang

https://clang.godbolt.org/z/r4xYWfPfe

edit: oh the article also mentions it now :)

Interesting. I thought modern CPU optimisation required avoiding branches, but here adding the branch allows the branch pediction to parallelise what it otherwise couldn't.

Brilliant! Hadn't seen this technique before.

I think this call for something similar to "__builtin_expect" or linux' likely()/unlikely().

Not very clean, but better than inserting obscure optimisations in the source.

latency optimization is a skill. I liked how you went till CSE pass. I myself wrote several passes to go to lowest latency possible

This is really surprising! I've never considered the possibility that using an equality test to skip a write that would be a no-op could break a dependency and thus lead to higher perf overall if the "equal" outcome occurs often enough. This might be applicable in many situations where you "edit" some data in-place, but most of the time there are few or no changes.

my js brain keeps thinking encoding[i] = next_j[i][j];