[MC] Explicitly use memcpy in emitBytes() (NFC) (#177187) We've observed a compile-time regression in LLVM 22 when including large blobs. The root cause was that emitBytes() was copying bytes one-by-one, which is much slower than using memcpy for large objects. Optimization of std::copy to memmove is apparently much less reliable than one might think. In particular, when using a non-bleeding-edge libstdc++ (anything older than version 15), this does not happen if the types of the input and output iterators do not match (like here, where there is a signed/unsigned mismatch). As this code is performance sensitive, I think it makes sense to directly use memcpy. Previously this code used SmallVector::append, which explicitly uses memcpy.
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.