[yvdriess]

Register moves do not really play a factor in performance, unless its to move to/from vector registers.

[CalChris]

H+P says register allocation is one of the most important—if not the most important—optimizations.

[yvdriess]

In cpu uarch design, sure, but that's outside the context of the discussion. There's nothing you can do to that C++ library you are optimizing that will impact performance due to register allocation/renaming.