On 16/11/12 18:38, Nevin Liber wrote:
On 16 November 2012 10:54, Yanchenko Maxim <maximyanchenko@yandex.ru> wrote:
Those are high-performance constructs. We can only pray that a compiler will be smart enough to convert our iterator-based code to memcpy/memcmp/memset, and from my experience compilers are not nearly as smart if it's slightly beyond trivial cases.
Now we are getting somewhere. Actual experience. Could you elaborate on the compilers and constructs that need to be hand optimized into equivalent code because the optimizers aren't doing it themselves? Or are there better constructs with size that aren't equivalent to their pointer counterparts?
Hand-optimized code is better than what you obtain through automated code generation optimization algorithms, since those algorithms are only as smart as the transformations the people who engineered them could make the system detect and do, and are therefore one-size-fits-all. On the other hand, hand-optimized code is optimized specially for the particular thing in question. memcpy on x86-64, for example, is typically 1.5x faster when specifically hand-optimized (and that's assuming the compiler detected that it could apply vectorization, which is most of the time not the case).