Originally posted by: FangLu

The XL C and XL C/C++ compilers support the following compiler options and function attributes that control function inlining.

• The noinline function attribute (IBM extension): prevents the function to which it is applied from being inlined.

• The always_inline function attribute (IBM extension): instructs the compiler to inline a function.

• The -qinline compiler option: attempts to inline functions instead of generating calls to those functions, for improved performance.

• The -qinline+<function_name> option: specifies that the named function must be inlined.

• The -qinline-<function_name> option: specifies that the named function must not be inlined.

• The -qnoinline option disables all inlining, including that achieved by the high-level optimizer with the -qipa option, and functions declared with the inline keyword.

To use these options and function attributes correctly, we must understand the following precedence relationships:

• The noinline function attribute takes precedence over the inlining compiler options (-qinline, -qinline+), the inline keyword, and the always_inline function attribute.

• The -qinline-<function_name> option takes higher precedence than the always_inline attribute.

• The always_inline attribute takes precedence over the -qnoinline option.