It doesn’t matter. Stricly speaking LEA can be executed in smaller number of execution units than INC on certain CPUs. For instance, on Haswell LEA can be executed in two different execution units (1, 5), and INC can be in four different execution units (0, 1, 5, 6). That said, compiler should be careful enough to not add LEA instruction when it would cause extra latency that INC wouldn’t. Performance is identical on pretty much every 64-bit CPU, including oldest ones.
On certain CPUs like Intel Atom or AMD K8/K10, LEA is executed in AGU instead of ALU. This means on Intel Atom, LEA is actually faster than INC, when surronded by arithmetic instructions, as LEA isn’t executed in ALU responsible for doing integer calculations. This means LEA can be executed in parallel to other arithmetic instructions.
Rust compiler for x86_64 platform by default tries to generate code for generic x86 64-bit CPU, which includes Intel Atom, which is why it optimizes usage of ALU and AGU. There is no real cost in doing so, other than making code faster on those CPUs.
You can try compiling the code for specifically CPU you are using with
-C target_cpu=native option, as opposed to trying to optimize for all CPUs that exist. Note that this code may not work on other CPUs, as it will use features implemented by that CPU.