[chas]

I also don't have any direct HFT experience, but I do know that HFT firms hire FPGA designers (https://www.indeed.com/q-Fpga-Engineer-Trading-jobs.html) which suggests they really care about counting cycles and basically everything in is play from a performance perspective.

To contribute to the OP, https://godbolt.org/ is indispensible for high-performance C++ development. In specific, you can see under what circumstances the compiler optimizations apply to your code.