As we will see there are multiple ways to implement the logic of these intrinsics. Some implementation methods are preferred because they allow the compiler to select instructions and provided the most flexibility for optimization across the whole sequence. Other methods may be required to deliver a specific semantic or to deliver better optimization than the current compiler is capable of. Some methods are more portable across multiple compilers (GCC, LLVM, ...). All of this should be taken into consideration for each intrinsic implementation. In general we should use the following list as a guide to these decisions: Use C vector arithmetic, logical, dereference, etc., operators in preference to intrinsics. Use the bi-endian interfaces from Appendix A of the ABI in preference to other intrinsics when available, as these are designed for portability among compilers. Use other, less well documented intrinsics (such as __builtin_vsx_*) when no better facility is available, in preference to assembly. If necessary, use inline assembly, but know what you're doing.