> LICM is a very simple thing to do.

Yeah, it sometimes surprises me how much value the most simple optimizations have and how much they break people's attempts to measure performance.

There is another side to this medal which is best expressed in a quote I picked up from a relatively old paper:

"A survey of the literature on optimization uncovers many techniques that are hard to understand, harder to implement, more general than necessary and of marginal value. Our approach was to do the most profitable machine independent optimizations in the most profitable way" (A Portable Optimizing Compiler for Modula-2 by Michael L. Powel)

In some sense the more microbenchmarks an optimization breaks the bigger its impact on real world code is :)