Can const-correctness improve performance?

Answer 1

const correctness is a good thing with respect to maintainability. Otherwise, clients of your class could break that class's internal members. For instance, consider the standard std::string::c_str() -- if it couldn't return a const value, you'd be able to screw around with the internal buffer of the string!

That said, any compiler worth it's salt is going to be able to detect if a variable is really constant or not, and apply correct optimizations. Don't use const for performance reasons. Use it for maintainability reasons.

Answer 2

in my experience, no

For scalar variables, compiler is able to determine whenever the value is changed and perform necessary optimization itself.

For array pointers, const correctness is no guarantee that values are really constant in presence of potential aliasing problems. Hence compiler can not use const modifier alone to perform optimizations

if you are looking optimization, you should consider __restrict__ or special function modifiers/attributes: http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html

Answer 3

A bit old, but still applies: http://www.gotw.ca/gotw/081.htm And some more: http://cpp-next.com/archive/2009/08/want-speed-pass-by-value/