Tech Off Post

Single Post Permalink

View Thread: (STL) move_if algorithm, what's your take on it ?
  • User profile image

    > Sometimes i do trust the compiler a bit too much thinking its smart enough to understand what i'm doing when it can be really stupid and stubborn sometimes.

    Compilers are good at micro-optimization, bad at macro-optimization. Humans are the reverse.

    > When ever i see 'back_inserter' i think of performance loss. Is that incorrect ?

    It's very convenient, and avoids length-related errors. However, for performance-critical code, capacity testing on every push_back(), and occasional reallocation, are significant.

    > What do you think about that 'find_if' "optimization" ?

    It's reasonable, but the test afterwards is still unnecessary.

    > 6. Nice catch. Btw how big of an issue is that ? Cant the compiler optimize that away ?

    Maybe, maybe not.

    > That surprised me a bit. Isn't (&&) and std::move's main reason for existing just because of reducing reallocation overhead ?

    They exist to eliminate unnecessary dynamic memory allocations and deallocations, which can be triggered by temporaries or vector reallocation, etc.

    > Now i'm a bit confused. When writing algorithms shouldn't you have reallocation overhead in mind or are there some simple guidelines you can follow  ?

    Yes, but you should also count your operations. 2N is a lot bigger than N.

    > 10. But it will not hurt performance right or is it bad in some way ?

    Shouldn't affect perf, it's just unnecessary.

    > Explain more, please.

    I was assuming that the whole source range would be discarded.

    > How big of an issue is it really that move_if use forward iterators ?

    Someone with input iterators who wants to use your algorithm will be sad. That someone may be you.

    > I'm beginning to understand the many decisions you must be making working on the STL for every single function.


    > How do you know when to stop: optimizing / correction cleaning and move on to the next thing ?

    I just try to fix bugs until my bug count reaches zero. I also fix todos on my todo list when I'm in the neighborhood.