In my experience from writing a toy compiler, the speedup you get with a reasonable set of optimizatios compared to spilling each temporary result to memory is

In my experience from writing a toy compiler, the speedup you get with a reasonable set of optimizatios compared to spilling each temporary result to memory is in the ballpark. There are vastly different situations of course, and very inefficient ways to write C vode that would require some compiler smartness, but 2x is a number that you'd have to contend with actual measured data to make the claims you made. In many cases I'd suspect the caches are doing exactly what you alluded to, masking inefficiencies of unnecessary writes to memory, at least to an extent. You might be able to demonstrate a speedup of 100x but I suspect it would take some work or possibly involve an artificial usecase.