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LLVM Prebuilt

This repository builds custom prebuilt toolchain packages for LLVM/Clang, Halide, Linux cctools, and platform SDK/toolchain support bundles. It is intended for reproducible GitHub Actions builds across the major desktop operating systems and CPU architectures used by downstream native projects.

You can download published packages from the GitHub releases page, or run the workflows in this repository to produce your own artifacts.

Packages

LLVM/Clang

The LLVM workflow builds minimal installable Clang/LLVM distributions with Clang, LLD, selected LLVM tools, development headers, CMake exports, zlib, and libxml2 support.

Currently built LLVM versions: 18.1.8, 20.1.8.

Arch Windows macOS Ubuntu 22.04 Ubuntu 24.04
x86_64 Yes Yes Yes Yes
aarch64 Yes Yes Yes Yes

Artifacts are named:

clang+llvm-<version>-<arch>-<os>.tar.xz

Halide

The Halide workflow builds Halide packages against LLVM artifacts produced by the LLVM workflow. It first installs a host LLVM package, then installs a target LLVM package when cross-compiling for aarch64.

Currently built Halide versions: 18.0.0, 19.0.0.

Arch Windows macOS Ubuntu 22.04 Ubuntu 24.04
x86_64 Yes Yes Yes Yes
aarch64 Yes Yes Yes Yes

Artifacts are named:

halide-<version>-<arch>-<os>.tar.xz

cctools

The cctools workflow builds Linux packages containing the Apple cctools port and supporting libraries.

Arch Windows macOS Ubuntu 22.04 Ubuntu 24.04
x86_64 No No Yes Yes
aarch64 No No Yes Yes

Artifacts are named:

cctools-<arch>-<os>.tar.xz

Platform Bundles

Additional workflows package host platform support files:

Workflow Artifact
MSVC bundle vctools.tar.xz, winsdk.tar.xz
Xcode bundle xcode-bundle.tar.xz

Repository Layout

Path Purpose
.github/workflows/llvm-prebuilt.yml Builds LLVM/Clang packages.
.github/workflows/halide-prebuilt.yml Builds Halide packages from LLVM workflow artifacts.
.github/workflows/cctools-prebuilt.yml Builds Linux cctools packages.
.github/workflows/github-release.yml Downloads workflow artifacts, creates checksums, and publishes a release.
cmake/*.cmake LLVM and Halide toolchain files plus LLVM distribution cache settings.
patches/*.patch Version-specific LLVM and Halide patches applied before configuration.
scripts/Get-UbuntuPackage.ps1 Resolves, downloads, and extracts Ubuntu packages for Linux cross-compilation.

Build Overview

LLVM builds use a two-stage flow:

  1. Build native host tools from llvm/llvm-project, including llvm-tblgen, clang-tblgen, and llvm-config.
  2. Configure and build the target distribution with the matching cmake/<arch>-<os>.cmake toolchain file and cmake/llvm-distribution.cmake initial cache.

The distribution surface is controlled by cmake/llvm-distribution.cmake. It enables Clang, clang-tools-extra, LLVM, LLD, the selected target backends, development headers/libraries, CMake exports, and selected toolchain utilities.

Halide builds follow a similar host/target split. Host tools such as build_halide_h, binary2cpp, and regexp_replace are built first, then reused through the HALIDE_HOST_TOOLS_DIR CMake option added by the repository patches.

Running the Workflows

All major package workflows are manually triggered with workflow_dispatch.

Recommended order:

  1. Run LLVM prebuilt.
  2. Run halide prebuilt with the LLVM workflow run ID, or use latest.
  3. Run cctools prebuilt if Linux cctools artifacts are needed.
  4. Run GitHub Release with the desired workflow run IDs to collect artifacts and publish a release.

The release workflow supports dry-run and draft-release inputs. Keep dry-run enabled while checking artifact collection and checksums.

Local Development Notes

The workflows use PowerShell heavily, including on Linux runners, so PowerShell-compatible commands are preferred when updating scripts or documentation.

For Linux aarch64 cross-compilation, do not hardcode Ubuntu .deb filenames. Use scripts/Get-UbuntuPackage.ps1, which maps Ubuntu releases to codenames, resolves current package filenames through packages.ubuntu.com, downloads the package, and extracts the data archive.

Patch files are version-specific. When adding or updating upstream LLVM or Halide versions, keep workflow conditionals and patch filenames in sync, then verify that patches apply cleanly before testing the build.

Generated upstream source trees and build directories should remain untracked. Common local directories include llvm-project, llvm-host, llvm-build, halide, halide-host, and halide-build.

Example LLVM Configure Commands

Build native host tools:

cmake -G Ninja -S llvm-project/llvm -B llvm-host `
	-DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra" `
	-DCMAKE_BUILD_TYPE=Release -Wno-dev

cmake --build llvm-host --target llvm-tblgen clang-tblgen llvm-config

Configure a target LLVM build:

cmake -G Ninja -S llvm-project/llvm -B llvm-build `
	-DCMAKE_INSTALL_PREFIX=llvm-install `
	-DCMAKE_TOOLCHAIN_FILE="$PWD/cmake/x86_64-ubuntu-24.04.cmake" `
	-C "$PWD/cmake/llvm-distribution.cmake" -Wno-dev

Build and install the distribution:

cmake --build llvm-build
cmake --build llvm-build --target install-distribution

Full local builds are large. For broad changes, start with an Ubuntu x86_64 LLVM build, then validate aarch64 cross-compilation and the Ubuntu release variants separately.