[WJW]

This depends on the compiler of course. Most will not because it is not worth it, but I expect that there is at least one compiler out there with the option to exhaustively search the allocation space for that very last nanosecond of runtime optimization. Probably inside an HFT firm somewhere.

[astrange]

There's some material on this under "superoptimizers", but I think if you want this then you should get an FPGA.