flang-releases

Flang (LLVM Fortran compiler) binaries with wasm32 cross-compilation support.

Platforms

Target	Host
x86_64-unknown-linux-gnu	Linux x86_64
aarch64-unknown-linux-gnu	Linux ARM64
x86_64-apple-darwin	macOS x86_64
arm64-apple-darwin	macOS ARM64
x86_64-pc-windows-msvc	Windows x86_64

Linux builds are compiled on Alpine (musl libc), producing portable binaries that work on any Linux distribution regardless of glibc version.

Each release includes libflang_rt.runtime.wasm32.a for cross-compiling Fortran to WebAssembly.

Release Assets

Release artifact naming is stable:

• flang+llvm-{version}-{target_triple}.tar.gz (Linux, macOS)
• flang+llvm-{version}-{target_triple}.zip (Windows)

Every release also includes:

• SHA256SUMS.txt
• release-metadata.json

Compiler entrypoints are normalized in every archive:

• Unix: bin/flang and bin/flang-new
• Windows: bin/flang.exe and bin/flang-new.exe

Usage

Download from Releases and extract.

# Native compilation
flang-new -o hello hello.f90

# Cross-compile to wasm32 (requires Emscripten)
flang-new -c --target=wasm32-unknown-emscripten -o hello.o hello.f90
emcc hello.o -L$FLANG/lib/clang/21/lib/wasm32-unknown-emscripten -lflang_rt.runtime.wasm32 -o hello.js

CMake

set(CMAKE_Fortran_COMPILER /path/to/flang-new)

Or via command line:

cmake -DCMAKE_Fortran_COMPILER=/path/to/flang-new ..

Make

FC = /path/to/flang-new
FFLAGS = -O2

%.o: %.f90
	$(FC) $(FFLAGS) -c $< -o $@

Bazel

Use with rules_fortran:

load("@rules_fortran//fortran:repositories.bzl", "flang_register_toolchains")

flang_register_toolchains()

Why

Fortran remains widely used in numerical computing, scientific simulation, and optimization libraries. This project enables running such code in browsers and other WebAssembly runtimes—useful for interactive demos, client-side computation, or porting legacy numerical code to the web.

Further Reading

• Fortran in the Browser (2020)
• Compile FORTRAN to WebAssembly and Solve Electromagnetic Fields in Web Browsers (2023)
• Fortran on WebAssembly (2024)
• LLVM Fortran Levels Up: Goodbye flang-new, Hello flang! (2025)
• math/openblas: switch to flang (2025)

Build

CI Topology

• ci-pr.yml: lightweight PR validation (Linux x86_64, preset linux-x86_64, wasm32 e2e)
• ci-full.yml: full 5-platform builds (scheduled Tue/Fri 01:00 UTC + manual)
• release.yml: release-only workflow, consumes artifacts from ci-full run or rebuilds

release.yml workflow_dispatch inputs:

• rebuild (bool): rebuild all platforms in release run
• source_run_id (string): consume artifacts from a specific ci-full run
• tag (string): override release tag
• version (string): single source of version truth for artifact/tag/build (recommended to fill this only)
• llvm_fork_repo (string, advanced): LLVM fork repo override
• llvm_fork_ref (string, advanced): LLVM fork ref override
• draft (bool): draft/public release toggle

When rebuild=false, release.yml downloads artifacts from an existing successful ci-full.yml run (same commit SHA by default, or explicit source_run_id). When rebuild=true, release.yml builds from llvm_fork_repo/llvm_fork_ref (input override or versions.env/auto defaults).

All build jobs use .github/workflows/_build-platform.yml.

LLVM Source Policy

LLVM source is pulled from fork, not from upstream llvm/llvm-project directly.

• LLVM_FORK_REPO and LLVM_FORK_REF are defined in versions.env
• CI fails immediately if LLVM_FORK_REF is empty
• Fork ref is expected to include wasm32 patch set already applied

EMSDK Selection Policy

EMSDK is selected automatically from emsdk-llvm-map.json based on build LLVM major.

• Selector: scripts/resolve_emsdk_for_llvm.py
• Validation: scripts/check_tool_llvm_major.py --tool llvm-nm
• CI fails if downloaded emsdk's llvm-nm --version major does not match mapped expectation.

versions.env still keeps EMSDK_VERSION/EMSDK_HASH as fallback metadata, but CI selection is map-driven.

Automatic LLVM Version Tracking

llvm-version-watch.yml runs daily and:

1. Finds latest LLVM patch version in TRACKED_LLVM_MINOR
2. Opens a PR when versions.env needs an update
3. Updates LLVM_VERSION and LLVM_FORK_REF using flang-wasm32-llvmorg-{version} convention