Comment by cogman10

My understanding of most optimizing compilers is that this is an extremely common "last step" sort of optimization. A lot of the optimizing work is beating the code into a canonical form where these sorts of templates can be readily applied.

It was also my understanding that that's also the point of "super optimizer"s [1] which look for these common patterns in something like LLVM IR to generate optimization targets for the mainline optimizer.

[1] https://en.wikipedia.org/wiki/Superoptimization