IIRC from our similar code, the LEA (load effective address) instruction is useful for doing adds / subtracts of arbitrary integers without updating the flags.

Flags turn out to be quite the annoyance for the kind of in-process virtualization needed by Time Travel Debug. You need to instrument code with minimal overhead so, on the one hand, you don't want to save/restore flags all the time .... And on the other hand it still all has to work when flags get used.