Performance 32 bit vs. 64 bit arithmetic

Question

Are native 64 bit integer arithmetic instructions slower than their 32 bit counter parts (on x86_64 machine with 64 bit O

Answer 1

I just stumbled upon this question, but I think one very important aspect is missing here: if you really look down into assembly code using the type 'int' for indices will likely slow down the code your compiler generates. This is because 'int' defaults to a 32bit type on many 64bit compilers and platforms (Visual Studio, GCC) and doing address calculations with pointers (which are necessarily 64bit on a 64bit OS) and 'int' will cause the compiler to emit unnecessary conversions between 32 and 64bit registers. I've just experienced this in a very performance critical inner loop of my code. Switching from 'int' to 'long long' as loop index improved my algorithm run time by about 10%, which was quite a huge gain considering the extensive SSE/AVX2 vectorization I was already using at that point.