panhaolin2001 / bazel_llvm

LLVM libraries and binaries for bazel

bazel_llvm: LLVM libraries and binaries for bazel

Overview

Pre-built LLVM releases to use as dependencies in bazel projects:

• @llvm//<version> provides a cc_library that can be used as dep for C++ apps in bazel that link against LLVM.
• @llvm//<vesion>:<bin> provides pre-built LLVM binaries, e.g. @llvm//10.0.0:clang provides clang 10 binary. This can be used as a data dep of scripts.

Supported compiler / OS versions:

• Ubuntu Linux 18.04 with clang / gcc >= 7.
• macOS >= 10.15.

Getting Started

Add the following to your WORKSPACE file:

http_archive(
    name = "llvm",
    strip_prefix = "bazel_llvm-<stable-commit>",
    urls = ["https://github.com/ChrisCummins/bazel_llvm/archive/<stable-commit>.tar.gz"],
)

load("@llvm//tools/bzl:deps.bzl", "llvm_deps")
llvm_deps()

In your BUILD files, reference @llvm//<version>:<target>:

# Link against LLVM 10.0.0 as a regular C++ dependency:
cc_library(
    name = "my_lib",
    srcs = ["my_lib.cc"],
    copts = ["-std=c++14", "-fno-rtti"],  # required
    deps = ["@llvm//10.0.0"],
)

# Use pre-compiled opt as a data dependency:
sh_binary(
    name = "my_script",
    srcs = ["my_script.sh"],
    data = ["@llvm//10.0.0:opt"],
)

See the examples directory for further usage.

Known issues

• This uses LLVM releases archives, which are Release builds without assertions enabled. To use a debug build, or one with assertions enabled, you would need to provide your own build archive and update the archives in tools/bzl/deps.bzl.

Work-in-progress: building from source

I have tried a couple of times to get LLVM to build from source as a cmake_external() target using rules_foreign_cc. I have yet to get it to work. There seems to be conflicts between the bazel build environment and the build environment that LLVM usually expects.

You can see my latest attempt here. I have a working Debug build on macOS, but now I get double-defined static variable errors when I link against it from a cc_library(). I don't have the patience to figure out enough about LLVM/Bazel build internals to crack it. If you want to give it a go, build:

$ bazel build @llvm//10.0.0:debug --sandbox_debug

Patches welcome! ❤️