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Glow is a machine learning compiler and execution engine for hardware accelerators. It is designed to be used as a backend for high-level machine learning frameworks. The compiler is designed to allow state of the art compiler optimizations and code generation of neural network graphs. This library is in active development. The project plan is described in the Github issues section and in the Roadmap wiki page.


Contributions to Glow are welcomed and encouraged! Glow is developed in collaboration with the following partners:

Bitmain Logo Habana Logo ST Logo
Cadence Logo Intel Logo Synopsys Logo
CEVA Logo Marvell Logo
Esperanto Logo NXP Logo

How does it work?

Glow lowers a traditional neural network dataflow graph into a two-phase strongly-typed intermediate representation (IR). The high-level IR allows the optimizer to perform domain-specific optimizations. The lower-level instruction-based address-only IR allows the compiler to perform memory-related optimizations, such as instruction scheduling, static memory allocation and copy elimination. At the lowest level, the optimizer performs machine-specific code generation to take advantage of specialized hardware features. Glow features a lowering phase which enables the compiler to support a high number of input operators as well as a large number of hardware targets by eliminating the need to implement all operators on all targets. The lowering phase is designed to reduce the input space and allow new hardware backends to focus on a small number of linear algebra primitives. The design philosophy is described in an arXiv paper.

Getting Started

System Requirements

Glow builds and runs on macOS and Linux. The software depends on a modern C++ compiler that supports C++11, on CMake, LLVM (>=7.0), glog, protocol buffers, and libpng.

Get Glow!

git clone  # or: git clone
cd glow


Glow depends on a few submodules: googletest, onnx, and a library for FP16 conversions.

To get them, from the glow directory, run:

git submodule update --init --recursive

Source dependencies

Glow depends on fmt, which must be built from source:

git clone
mkdir fmt/build
cd fmt/build
cmake ..
sudo make install


Install the required dependencies using either Homebrew or MacPorts. If using Homebrew, run:

brew install cmake graphviz libpng ninja protobuf wget glog autopep8 llvm   \
    boost double-conversion gflags jemalloc libevent lz4 openssl pkg-config \
    snappy xz

If using MacPorts, run:

port install cmake graphviz libpng ninja protobuf-cpp wget google-glog \
    boost double-conversion gflags jemalloc libevent lz4 openssl snappy xz
# Choose version >= 7
port install llvm-$LLVM_VERSION.0 

Note that LLVM is installed in a non-default location to avoid conflicts with the system's LLVM --Homebrew usually installs LLVM in /usr/local/opt/llvm/, whereas MacPorts installs it in /opt/local/libexec/llvm-$LLVM_VERSION.0/. This means that CMake will need to be told where to find LLVM when building; instructions on that can be found here.

Finally, create a symbolic link to the Homebrew- or MacPorts-installed clang-* tools so that the utils/ script is able to find them later on. For a Homebrew-managed installation, run:

ln -s "/usr/local/opt/llvm/bin/clang-format" "/usr/local/bin/clang-format"
ln -s "/usr/local/opt/llvm/bin/clang-tidy" "/usr/local/bin/clang-tidy"

For MacPorts, run:

ln -s "/opt/local/libexec/llvm-$LLVM_VERSION.0/bin/clang-format" "/usr/local/bin/clang-format"
ln -s "/opt/local/libexec/llvm-$LLVM_VERSION.0/bin/clang-tidy" "/usr/local/bin/clang-tidy"

Note: Starting with macOS Mojave, Xcode's command line tools changed header layout. In order for Glow to build on Mojave, you might need to install macOS_SDK_headers_for_macOS_10.14.pkg, located in /Library/Developer/CommandLineTools/Packages/. For macOS Catalina you might need to explicitly specify SDKROOT: export SDKROOT="/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk"


[The following instructions have been tested on Ubuntu 16.04 and 18.04]

In order to build Glow on Ubuntu it is necessary to install a few packages. The following command should install the required dependencies:

sudo apt-get install clang clang-8 cmake graphviz libpng-dev \
    libprotobuf-dev llvm-8 llvm-8-dev ninja-build protobuf-compiler wget \
    opencl-headers libgoogle-glog-dev libboost-all-dev \
    libdouble-conversion-dev libevent-dev libssl-dev libgflags-dev \
    libjemalloc-dev libpthread-stubs0-dev liblz4-dev libzstd-dev libbz2-dev \
    libsodium-dev libfmt-dev

[Note: Ubuntu 16.04 and 18.04 ship with llvm-6 and need to be upgraded before building Glow. Building Glow on Ubuntu 16.04 with llvm-7 fails because llvm-7 xenial distribution uses an older c++ ABI, however building Glow on Ubuntu 18.04 with llvm-7 has been tested and is successful]

It may be desirable to use update-alternatives to manage the version of clang/clang++:

sudo update-alternatives --install /usr/bin/clang clang \
    /usr/lib/llvm-8/bin/clang 50
sudo update-alternatives --install /usr/bin/clang++ clang++ \
    /usr/lib/llvm-8/bin/clang++ 50

Glow uses the system default C/C++ compiler (/usr/bin/c++), and so you may also want to switch your default C/C++ compiler to clang:

sudo update-alternatives --config cc
    # Select the option corresponding to /usr/bin/clang ...
sudo update-alternatives --config c++
    # Select the option corresponding to /usr/bin/clang++ ...

Glow should build just fine with gcc (e.g. gcc 5.4), but we mostly use clang and are more attentive to compatibility with clang.

Finally, in order to support the ONNX net serialization format, Glow requires protobuf >= 2.6.1, but the above command may install older version on older Ubuntu (e.g. 14.04). If this is the case, we suggest to look at utils/ to install a newer version from source.

For details on installing OpenCL on Ubuntu please see these instructions.

Configure and Build

To build the compiler, create a build directory and run cmake on the source directory. It's a good idea to build two configurations (Release and Debug) because some programs take a really long time to run in Debug mode. It's also a good idea to build the project outside of the source directory.

mkdir build_Debug
cd build_Debug
cmake -G Ninja -DCMAKE_BUILD_TYPE=Debug ../glow
ninja all

It's possible to configure and build the compiler with any CMake generator, like GNU Makefiles, Ninja and Xcode build.

For platform-specific build instructions and advanced options, such as building with Address-Sanitizers refer to this guide: Building the Compiler.

If you're running macOS v10.14 (Mojave) and ninja all fails because it can't find headers (e.g. string.h), run this command to fix it, and try again. More information is available here under "Command Line Tools".

open /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg

For macOS v10.15 (Catalina) you might need to explicitly specify SDKROOT:

export SDKROOT="/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk"

Building with dependencies (LLVM)

By default, Glow will use a system provided LLVM. Note that Glow requires LLVM 7.0 or later. If you have LLVM installed in a non-default location (for example, if you installed it using Homebrew on macOS), you need to tell CMake where to find llvm using -DLLVM_DIR. For example, if LLVM were installed in /usr/local/opt:

cmake -G Ninja ../glow \

If LLVM is not available on your system you'll need to build it manually. Run the script '/utils/ to clone, build and install LLVM in a local directory. You will need to configure Glow with the flag -DLLVM_DIR to tell the build system where to find LLVM given the local directory you installed it in (e.g. -DLLVM_DIR=/path/to/llvm_install/lib/cmake/llvm if using

Testing and Running

Unit tests

The project has a few unit tests in the tests/unittests subdirectory. To run all of them, simply run ninja test.

C++ API examples

A few test programs that use Glow's C++ API are found under the examples/ subdirectory. The mnist, cifar10, fr2en and ptb programs train and run digit recognition, image classification and language modeling benchmarks, respectively.

To run these programs, build Glow in Release mode, then run the following commands to download the cifar10, mnist and ptb databases.

python ../glow/utils/ --all-datasets

Now run the examples. Note that the databases should be in the current working directory.


If everything goes well you should see:

  • mnist: pictures from the mnist digits database
  • cifar10: image classifications that steadily improve
  • fr2en: an interactive French-to-English translator
  • ptb: decreasing perplexity on the dataset as the network trains
  • char-rnn: generates random text based on some document

Note that the default build mode is Debug, which means that the compiler itself is easy to debug because the binary contains debug info, lots of assertions, and the optimizations are disabled. It also means that the compiler and runtime are very slow, and the execution time can be hundreds of times slower than that of release builds. If you wish to benchmark the compiler, run long benchmarks, or release the product then you should compile the compiler in Release mode. Check the main CMake file for more details.

More details on testing and running Glow can be found in: Testing the Glow Compiler.

Ahead-of-time Compilation

Glow can be used to compile neural networks into object files containing native code. We provide resnet50 (both quantized and non-quantized versions) as an example of this capability in examples/bundles/resnet50. See Creating Standalone Executable Bundles for more detail.


To get started contributing, please refer to the following guides:


  • Forums: discuss implementations, research, etc: Make sure to label topic with the "glow" category.
  • GitHub issues: bug reports, feature requests, install issues, RFCs, thoughts, etc.


Glow is licensed under the Apache 2.0 License.