Thinking about it even more - if you did see a speedup and you had the ability to analyze why it sped up, then I bet that increased work in the cpu would be the

Thinking about it even more - if you did see a speedup and you had the ability to analyze why it sped up, then I bet that increased work in the cpu would be the cause sooner than icache pressure. On x86, I think that an instruction with a memory address always takes a cycle to compute it no matter how simple or hard it is, so if you do the computation in a separate instruction, you are likely to add cycles.