The extent to which suggestions made by using the register storage-class specifier are effective (6.7.1).
The number of effective register declarations depends on patterns of use and definition within each function and is bounded by the number of registers available for allocation. Neither the compiler nor the optimizer is required to honor register declarations.
The extent to which suggestions made by using the inline function specifier are effective (6.7.4).
The inline keyword is effective in causing the inlining of code only when using optimization, and only when the optimizer determines it is profitable to inline. See A.1.1 Optimization and Performance Options for a list of optimization options.