[clang][deps] Implement efficient in-process `ModuleCache` (#129751) The dependency scanner uses implicitly-built Clang modules under the hood. This system was originally designed to handle multiple concurrent processes working on the same module cache, and mutual exclusion was implemented using file locks. The scanner, however, runs within single process, making file locks unnecessary. This patch virtualizes the interface for module cache locking and provides an implementation based on `std::shared_mutex`. This reduces `clang-scan-deps` runtime by ~17% on my benchmark. Note that even when multiple processes run a scan on the same module cache (and therefore don't coordinate efficiently), this should still be correct due to the strict context hash, the write-through `InMemoryModuleCache` and the logic for rebuilding out-of-date or incompatible modules.
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.
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.
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.