Developer Guide and Reference

Contents

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
    .)

Product and Performance Information

1

Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

Notice revision #20110804