Compiler built-in functions

A built-in function is a coding extension to C that allows a programmer to use the syntax of C function calls and C variables to access the instruction set of the processor of the compiling machine. IBM® Power® architectures have special instructions that enable the development of highly optimized applications. Access to some Power instructions cannot be generated using the standard constructs of the C language. Other instructions can be generated through standard constructs, but using built-in functions allows exact control of the generated code. Inline assembly language programming, which uses these instructions directly, is fully supported starting from XL C, V12.1. Furthermore, the technique can be time-consuming to implement.

As an alternative to managing hardware registers through assembly language, XL C built-in functions provide access to the optimized Power instruction set and allow the compiler to optimize the instruction scheduling.

The following sections describe the available built-in functions for the AIX® platform.