4aeb2e60df
This patch introduces configuration for a Bazel BUILD in a side directory in the monorepo. This is following the approval of https://github.com/llvm/llvm-www/blob/main/proposals/LP0002-BazelBuildConfiguration.md As detailed in the README, the Bazel BUILD is not supported by the community in general, and is maintained only by interested parties. It follows the requirements of the LLVM peripheral tier: https://llvm.org/docs/SupportPolicy.html#peripheral-tier. This is largely copied from https://github.com/google/llvm-bazel, with a few filepath tweaks and the addition of the README. Reviewed By: echristo, keith, dblaikie, kuhar Differential Revision: https://reviews.llvm.org/D90352
4.7 KiB
Introduction
Warning The Bazel build is experimental and best-effort, supported in line with the policy for LLVM's peripheral support tier. LLVM's official build system is CMake. If in doubt use that. If you make changes to LLVM, you're expected to update the CMake build but you don't need to update Bazel build files. Reviewers should not ask authors to update Bazel build files unless the author has opted in to support Bazel. Keeping the Bazel build files up-to-date is on the people who use the Bazel build.
Bazel is a multi-language build system focused on reproducible builds to enable dependency analysis and caching for fast incremental builds.
The main motivation behind the existence of an LLVM Bazel build is that a number of projects that depend on LLVM use Bazel, and Bazel works best when it knows about the whole source tree (as opposed to installing artifacts coming from another build system). Community members are also welcome to use Bazel for their own development as long as they continue to maintain the official CMake build system. See also, the proposal for adding this configuration.
Quick Start
git clone https://github.com/llvm/llvm-project.git; cd llvm-projectif you don't have a checkout yet.- Install Bazel at the version indicated by .bazelversion, following the official instructions, if you don't have it installed yet: https://docs.bazel.build/versions/master/install.html.
cd utils/bazelbazel build --config=generic_clang @llvm-project//...(if building on Unix with Clang).--config=generic_gccand--config=msvcare also available.
Configuration
The repository .bazelrc will import user-specific settings from a
user.bazelrc file (in addition to the standard locations). Adding your typical
config setting is recommended.
build --config=generic_clang
You can enable disk caching, which will cache build results
build --disk_cache=~/.cache/bazel-disk-cache
You can instruct Bazel to use a ramdisk for its sandboxing operations via --sandbox_base, which can help avoid IO bottlenecks for the symlink stragegy used for sandboxing. This is especially important with many inputs and many cores (see https://github.com/bazelbuild/bazel/issues/11868):
build --sandbox_base=/dev/shm
Bear in mind that this requires that your ramdisk is of sufficient size to hold any temporary files. Anecdotally, 1GB should be sufficient.
Coverage
The LLVM, MLIR, and Clang subprojects have configurations for Linux (Clang and GCC), Mac (Clang and GCC), and Windows (MSVC). Configuration options that are platform-specific are selected for in defines. Many are also hardcoded to the values currently used by all supported configurations. If there is a configuration you'd like to use that isn't supported, please send a patch.
Usage
To use in dependent projects using Bazel, you can import LLVM (e.g. as a
submodule or using http_archive) and then use the provided configuration rule.
FIXME: This needs to be updated to a commit that exists once such a commit
exists.
FIXME: It shouldn't be necessary to configure http_archive twice for the same
archive (though caching means this isn't too expensive).
load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
LLVM_COMMIT = "0a1f0ee78122fc0642e8a1a18e1b2bc89c813387"
LLVM_SHA256 = "4f59737ccfdad2cfb4587d796ce97c1eb5433de7ea0f57f248554b83e92d81d2"
http_archive(
name = "llvm-project-raw",
build_file_content = "#empty",
sha256 = LLVM_SHA256,
strip_prefix = "llvm-project-" + LLVM_COMMIT,
urls = ["https://github.com/llvm/llvm-project/archive/{commit}.tar.gz".format(commit = LLVM_COMMIT)],
)
http_archive(
name = "llvm-bazel",
sha256 = LLVM_SHA256,
strip_prefix = "llvm-project-{}/utils/bazel".format(LLVM_COMMIT),
urls = ["https://github.com/llvm/llvm-project/archive/{commit}.tar.gz".format(commit = LLVM_COMMIT)],
)
load("@llvm-bazel//:configure.bzl", "llvm_configure")
llvm_configure(
name = "llvm-project",
src_path = ".",
src_workspace = "@llvm-project-raw//:WORKSPACE",
)
load("@llvm-bazel//:terminfo.bzl", "llvm_terminfo_system")
maybe(
llvm_terminfo_system,
name = "llvm_terminfo",
)
load("@llvm-bazel//:zlib.bzl", "llvm_zlib_system")
maybe(
llvm_zlib_system,
name = "llvm_zlib",
)