[tylerhou]

Nit: If a variable/object is only being written, that’s fine. There is a data dependency here because there is a read after a write.

I don’t have enough compiler knowledge to be able to definitively answer your question, but I think it would be a reasonable heuristic to favor emitting a branch over a cmov in cases where the cmov participates in a loop-carried data dependency.

The other advantage of emitting a branch is that branch prediction can better adapt to runtime conditions. Branch prediction tends to struggle when data is perfectly random, but most data is not. So in general it’s also reasonable for compilers to default to emitting branches.