Your program is well-formed and free of undefined behaviour, as far as I can tell. The C++ abstract machine never actually assigns to a const object. A not-taken if() is sufficient to “hide”https://stackoverflow.com/”protect” things that would be UB if they executed. The only thing an if(false) can’t save you from is an ill-formed program, e.g. … Read more
I hope this helps more than hurts 🙂 I did a little compiler shootout sometime over a year ago, and I am going off memory. GCC 4.2 (Apple) Intel 10 GCC 4.2 (Apple) + LLVM I tested multiple template heavy audio signal processing programs that I’d written. Compilation times: The Intel compiler was by far … Read more
This original answer was valid back in 2013. As of 2017 hardware, things have changed enough that both the question and the answer are out-of-date. See the end of this answer for the 2017 update. Original Answer (2013): Because you’re bottlenecked by memory bandwidth. While vectorization and other micro-optimizations can improve the speed of computation, … Read more
Strangely I have a simple answer: Because ICC isn’t optimal. When you write own compiler you get started with some very basic set of operation codes: NOP, MOV, ADD… up to 10 opcodes. You don’t use SUB for a while because it might easily be replaced by: ADD NEGgative operand. NEG isn’t basic as well, … Read more
In both cases the arguments and results are passed only in registers, as per the respective calling conventions on Windows and GNU/Linux. In the GNU/Linux variant, the xmm1 is used for accumulating the sum. Since it’s a call-clobbered register (a.k.a caller-saved) it’s stored (and restored) in the stack frame of the caller on each call. … Read more