[fmstephe]

So would you say in the general case, i.e. the compiler obviously doesn't know how predictable a branch may be, using conditional move is a poor choice when writing to an address which is repeatedly written to inside the loop?

What I am trying to get a feel for, is whether this represents a bad choice of assembly in general for this kind of loop.

[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.