It can't be otherwise if you're just assuming a straightforward compilation model where your written roughly reflects the assembly code that's generated. This just isn't the case with better compilers though.

For instance, Haskell can often perform rewrites or fusion passes that entirely eliminates the loop and all intermediate data structures, effectively giving a near-infinite speedup compared to alternatives. You typically can't perform such optimizations when side-effects are in the middle of the computation, for numerous reasons.