# Comparison of Function Order Lists and IPO Code Layout

The Intel® compiler provides two methods of optimizing the layout of functions in the executable:

- Using a function order list

- Using the /Qipo (Windows) compiler option

Each method has advantages. A function order list, created with proforder, lets you optimize the layout of non-static functions (external and library functions whose names are exposed to the linker).

The linker cannot directly affect the layout order for static functions because the names of these functions are not available in the object files.

The compiler cannot affect the layout order for functions it does not compile, such as library functions. The function layout optimization is performed automatically when IPO is active.

Alternately, using the /Qipo (Windows) option allows you to optimize the layout of all static or extern functions compiled with the Intel® C++ Compiler. The compiler cannot affect the layout order for functions it does not compile, such as library functions. The function layout optimization is performed automatically when IPO is active.

Function Order List Effects

Function Type | IPO Code Layout | Function Ordering with proforder
--- | --- | ---
Static | X | No effect
Extern | X | X
Library | No effect | X

Function Order List Usage Guidelines (Windows*)

Use the following guidelines to create a function order list:

- The order list only affects the order of non-static functions.

- You must compile with /Gy to enable function-level linking. (This option is active if you specify either option /O1 or /O2.)

Parent topic: PGO Tools