Profile-guided optimization (PGO, sometimes pronounced as ''pogo''), also known as profile-directed feedback (PDF), and feedback-directed optimization (FDO) is a compiler optimization technique 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 ...

that uses profiling to improve program runtime performance.

Method

Optimization techniques based on

static program analysis In computer science, static program analysis (or static analysis) is the analysis of computer programs performed without executing them, in contrast with dynamic program analysis, which is performed on programs during their execution. The term ...

of the

source code In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the w ...

consider code performance improvements without actually executing the program. No

dynamic program analysis Dynamic program analysis is the analysis of computer software that is performed by executing programs on a real or virtual processor. For dynamic program analysis to be effective, the target program must be executed with sufficient test inputs ...

is performed. The analysis may even consider code within loops including the number of times the loop will execute, for example in

loop unrolling Loop unrolling, also known as loop unwinding, is a loop transformation technique that attempts to optimize a program's execution speed at the expense of its binary size, which is an approach known as space–time tradeoff. The transformation ...

. In the absence of all the run time information, static program analysis can not take into account how frequently that code section is actually executed. The first high-level compiler, introduced as the Fortran Automatic Coding System in 1957, broke the code into blocks and devised a table of the frequency each block is executed via a simulated execution of the code in a

Monte Carlo Monte Carlo (; ; french: Monte-Carlo , or colloquially ''Monte-Carl'' ; lij, Munte Carlu ; ) is officially an administrative area of the Principality of Monaco, specifically the ward of Monte Carlo/Spélugues, where the Monte Carlo Casino is ...

fashion in which the outcome of conditional transfers (as via IF-type statements) is determined by a

random number generator Random number generation is a process by which, often by means of a random number generator (RNG), a sequence of numbers or symbols that cannot be reasonably predicted better than by random chance is generated. This means that the particular outc ...

suitably weighted by whatever FREQUENCY statements were provided by the programmer. Rather than programmer-supplied frequency information, profile-guided optimization uses the results of profiling test runs of the instrumented program to optimize the final generated code. The compiler accesses profile data from a sample run of the program across a representative input set. The results indicate which areas of the program are executed more frequently, and which areas are executed less frequently. All optimizations benefit from profile-guided feedback because they are less reliant on

heuristic A heuristic (; ), or heuristic technique, is any approach to problem solving or self-discovery that employs a practical method that is not guaranteed to be optimal, perfect, or rational, but is nevertheless sufficient for reaching an immediate ...

s when making compilation decisions. The caveat, however, is that the sample of data fed to the program during the profiling stage must be statistically representative of the typical usage scenarios; otherwise, profile-guided feedback has the potential to harm the overall performance of the final build instead of improving it.

Just-in-time compilation In computing, just-in-time (JIT) compilation (also dynamic translation or run-time compilations) is a way of executing computer code that involves compilation during execution of a program (at run time) rather than before execution. This may co ...

can make use of runtime information to dynamically recompile parts of the executed code to generate a more efficient native code. If the dynamic profile changes during execution, it can deoptimize the previous native code, and generate a new code optimized with the information from the new profile.

Adoption

There is support for building

Firefox Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko rendering engine to display web pages, which implements current ...

using PGO.Building with Profile-Guided Optimization
mozilla.org, 13 August 2013 Even though PGO is effective, it has not been widely adopted by software projects, due to its tedious dual-compilation model. It is also possible to perform PGO without instrumentation by collecting a profile using hardware performance counters.Dehao Chen (2010),
Taming hardware event samples for fdo compilation
, ''Proceedings of the 8th annual IEEE/ACM international symposium on Code generation and optimization'', pp. 42–52. This sampling-based approach has a much lower overhead and does not require a special compilation. The HotSpot Java virtual machine (JVM) uses profile-guided optimization to dynamically generate native code. As a consequence, a software binary is optimized for the actual load it is receiving. If the load changes,

adaptive optimization Adaptive optimization is a technique in computer science that performs dynamic recompilation of portions of a program based on the current execution profile. With a simple implementation, an adaptive optimizer may simply make a trade-off between ...

can dynamically recompile the running software to optimize it for the new load. This means that all software executed on the HotSpot JVM effectively make use of profile-guided optimization. PGO has been adopted in the Microsoft Windows version of Google Chrome. PGO was enabled in the

64-bit In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit CPUs and ALUs are those that are based on processor registers, address buses, or data buses of that size. A compu ...

edition of Chrome starting with version 53 and version 54 for the 32-bit edition. Google published a paper describing a system (AutoFDO) in use for using production profiles to guide builds resulting in up to a 10% performance improvement.

Implementations

Examples of compilers that implement PGO are: *

Intel C++ Compiler Intel oneAPI DPC++/C++ Compiler and Intel C++ Compiler Classic are Intel’s C, C++, SYCL, and Data Parallel C++ (DPC++) compilers for Intel processor-based systems, available for Windows, Linux, and macOS operating systems. Overview Intel ...

and Fortran compilers *

GNU Compiler Collection The GNU Compiler Collection (GCC) is an optimizing compiler produced by the GNU Project supporting various programming languages, hardware architectures and operating systems. The Free Software Foundation (FSF) distributes GCC as free softwar ...

compilers * Oracle Solaris Studio (formerly called Sun Studio) *

Microsoft Visual C++ Microsoft Visual C++ (MSVC) is a compiler for the C, C++ and C++/CX programming languages by Microsoft. MSVC is proprietary software; it was originally a standalone product but later became a part of Visual Studio and made available in both tri ...

compiler *

Clang Clang is a compiler front end for the C, C++, Objective-C, and Objective-C++ programming languages, as well as the OpenMP, OpenCL, RenderScript, CUDA, and HIP frameworks. It acts as a drop-in replacement for the GNU Compiler Collection ...

* IBM XL C/C++ *

GraalVM GraalVM is a Java VM and JDK based on HotSpot/OpenJDK, implemented in Java. It supports additional programming languages and execution modes, like ahead-of-time compilation of Java applications for fast startup and low memory footprint. The f ...

Enterprise Edition

References

{{Compiler optimizations Compiler optimizations

Method

Adoption

Implementations

See also

References