Do I have to include some header files in order to use GCC built_in function?

Question

The motivation is that I want to tell the compiler that my float *U array is 64 bytes aligned so that the compiler can do the vectorizations.

If using Intel compiler, I can use the __assume_aligned(U,64);I googled and found that if I want to do the same thing using GCC, I have to define another float *U_tmp=__builtin_assume_aligned(U,64), and use U_tmp. However, when it goes to compilation with GCC, the compiler reports that "error: ‘__builtin_assume_aligned’ was not declared in this scope" I don't know if I have missed some libraries or header files containing this GCC built in function.

Answer 1

This is supposed to work out of the box, without any additional headers. However, this has been added only to GCC 4.7, maybe your compiler is older than that?