Interprocedural optimization (IPO) is a collection of
compiler
In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...
techniques used in
computer programming
Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as anal ...
to improve performance in programs containing many frequently used
functions of small or medium length. IPO differs from other
compiler optimizations
In computing, an optimizing compiler is a compiler that tries to minimize or maximize some attributes of an executable computer program. Common requirements are to minimize a program's execution time, memory footprint, storage size, and power con ...
because it analyzes the entire program; other optimizations look at only a single function, or even a single block of code.
IPO seeks to reduce or eliminate duplicate calculations, inefficient use of memory, and to simplify iterative sequences such as loops. If there is a call to another routine that occurs within a loop, IPO analysis may determine that it is best to
inline that. Additionally, IPO may re-order the routines for better memory layout and
locality
Locality may refer to:
* Locality (association), an association of community regeneration organizations in England
* Locality (linguistics)
* Locality (settlement)
* Suburbs and localities (Australia), in which a locality is a geographic subdivi ...
.
IPO may also include typical compiler optimizations on a whole-program level, for example
dead code elimination
In compiler theory, dead-code elimination (also known as DCE, dead-code removal, dead-code stripping, or dead-code strip) is a compiler optimization to remove code which does not affect the program results. Removing such code has several benefits: ...
(DCE), which removes code that is never executed. To accomplish this, the compiler tests for branches that are never taken and removes the code in that branch. IPO also tries to ensure better use of constants. Modern compilers offer IPO as an option at compile-time. The actual IPO process may occur at any step between the human-readable source code and producing a finished executable binary program.
For languages that compile on a file-by-file basis, effective IPO across translation units (module files) requires knowledge of the "entry points" of the progra