b9d40a7ae4
The profile density feature(the amount of samples in the profile relative to the program size) is used to identify insufficient sample issue and provide hints for user to increase sample count. A low-density profile can be inaccurate due to statistical noise, which can hurt FDO performance. This change introduces two improvements to the current density work. 1. The density calculation/definition is changed. Previously, the density of a profile was calculated as the minimum density for all warm functions (a function was considered warm if its total samples were within the top N percent of the profile). However, there is a problem that a high total sample profile can have a very low density, which makes the density value unstable. - Instead, we want to find a density number such that if a function's density is below this value, it is considered low-density function. We consider the whole profile is bad if a group of low-density functions have the sum of samples that exceeds N percent cut-off of the total samples. - In implementation, we sort the function profiles by density, iterate them in descending order and keep accumulating the body samples until the sum exceeds the (100% - N) percentage of the total_samples, the profile-density is the last(minimum) function-density of processed functions. We introduce the a flag(`--profile-density-threshold`) for this percentage threshold. 2. The density is now calculated based on final(compiler used) profiles instead of merged context-less profiles.
The LLVM Compiler Infrastructure
Welcome to the LLVM project!
This repository contains the source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and run-time environments.
The LLVM project has multiple components. The core of the project is itself called "LLVM". This contains all of the tools, libraries, and header files needed to process intermediate representations and convert them into object files. Tools include an assembler, disassembler, bitcode analyzer, and bitcode optimizer.
C-like languages use the Clang frontend. This component compiles C, C++, Objective-C, and Objective-C++ code into LLVM bitcode -- and from there into object files, using LLVM.
Other components include: the libc++ C++ standard library, the LLD linker, and more.
Getting the Source Code and Building LLVM
Consult the Getting Started with LLVM page for information on building and running LLVM.
For information on how to contribute to the LLVM project, please take a look at the Contributing to LLVM guide.
Getting in touch
Join the LLVM Discourse forums, Discord chat, LLVM Office Hours or Regular sync-ups.
The LLVM project has adopted a code of conduct for participants to all modes of communication within the project.