[RISCV] Convert LWU to LW if possible in RISCVOptWInstrs (#144703) After the refactoring in #149710 the logic change is trivial. Motivation for preferring sign-extended 32-bit loads (LW) vs zero-extended (LWU): * LW is compressible while LWU is not. * Helps to minimise the diff vs RV32 (e.g. LWU vs LW) * Helps to minimise distracting diffs vs GCC. I see this come up frequently when comparing GCC code and in these cases it's a red herring. Similar normalisation could be done for LHU and LH, but this is less well motivated as there is a compressed LHU (and if performing the change in RISCVOptWInstrs it wouldn't be done for RV32). There is a compressed LBU but not LB, meaning doing a similar normalisation for byte-sized loads would actually be a regression in terms of code size. Load narrowing when allowed by hasAllNBitUsers isn't explored in this patch. This changes ~20500 instructions in an RVA22 build of the llvm-test-suite including SPEC 2017. As part of the review, the option of doing the change at ISel time was explored but was found to be less effective.
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.