There are several issues in defining “restrict” in C++, some of them are listed in WG paper N3635: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3635.pdf “Towards restrict-like semantics for C++” Some possible issues with restrict in C++ are: Restrict Class members and indirection with “this pointer” Passing of restrict qualifiers into functions, functors, lambdas, and templates Escaping of restrict pointer values … Read more
The restrict keyword does a difference. I’ve seen improvements of factor 2 and more in some situations (image processing). Most of the time the difference is not that large though. About 10%. Here is a little example that illustrate the difference. I’ve written a very basic 4×4 vector * matrix transform as a test. Note … Read more
restrict says that the pointer is the only thing that accesses the underlying object. It eliminates the potential for pointer aliasing, enabling better optimization by the compiler. For instance, suppose I have a machine with specialized instructions that can multiply vectors of numbers in memory, and I have the following code: void MultiplyArrays(int* dest, int* … Read more
In his paper, Memory Optimization, Christer Ericson says that while restrict is not part of the C++ standard yet, that it is supported by many compilers and he recommends it’s usage when available: restrict keyword ! New to 1999 ANSI/ISO C standard ! Not in C++ standard yet, but supported by many C++ compilers ! … Read more