Fair critique! I should perhaps not be benchmarking at 6AM. Fortunately it's no longer 6AM. > if the 0..100 is changed to 0_i64..100 I misread this initiall

Fair critique! I should perhaps not be benchmarking at 6AM. Fortunately it's no longer 6AM. > if the 0..100 is changed to 0_i64..100 I misread this initially as a complaint about the tweak to assembly iteration duration instead of a comment on tweaks to the author's Rust code (not enough caffeine). I did make the rust version worse by encoding a 64-bit immediate value in the inner loop's cmp, when the original was dealing with an 8-bit immediate value, so it's a fair complaint, even if you didn't make it ;). I've updated my code to attempt to correct for this deficiency as well. > Your conclusion would be correct if you got the same results after controlling for the other variables, i.e. make the C++ use inc & cmp, or the Rust use dec. V2: https://gist.github.com/MaulingMonkey/870c2fd1dc3e4f1b766199d05baf04b0 https://gist.github.com/MaulingMonkey/870c2fd1dc3e4f1b766199... Comparing: ..._rust vs ..._rust_ref, the only difference in the assembly is if I dereference inside or outside the loop. I've included two benchmarking passes of an identical program: In one, the version that dereferences inside the loop tends to actually perform faster (173ns vs 179ns per inner loop and setup/teardown thereof). In the other, performance tends to be identical: 173ns, the lower of the two. In-loop dereferencing performing better makes little enough sense to me that I'm inclined to err on the side of "this is neither an optimization nor a deoptimization", although the pattern is occuring regularly enough even with different stretch values that I'm really curious as to what's going on. EDIT: I believe I've figured it out - when comparing _cpp_deref vs _cpp (again, only difference being where I dereference, inside or outside the loop): Whichever I place further from stretch_benchmark / just_ret in foo.asm tends to be faster by up to 30ns. This applies to the rust versions too. I'm more likely measuring icache or similar than real performance differences between the two loops.