LLVM/SPIR-V Bi-Directional Translator

This repository contains source code for the LLVM/SPIR-V Bi-Directional Translator, a library and tool for translation between LLVM IR and SPIR-V.

The LLVM/SPIR-V Bi-Directional Translator is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt.

Directory Structure

The files/directories related to the translator:

• include/LLVMSPIRVLib.h - header file
• lib/SPIRV - library for SPIR-V in-memory representation, decoder/encoder and LLVM/SPIR-V translator
• tools/llvm-spirv - command line utility for translating between LLVM bitcode and SPIR-V binary

Build Instructions

The master branch of this repo is aimed to be buildable with the latest LLVM master revision.

Build with pre-installed LLVM

The translator can be built with the latest(nightly) package of LLVM. For Ubuntu and Debian systems LLVM provides repositories with nightly builds at http://apt.llvm.org/. For example the latest package for Ubuntu 16.04 can be installed with the following commands:

wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
sudo add-apt-repository "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial main"
sudo apt-get update
sudo apt-get install llvm-12-dev llvm-12-tools clang-12 libclang-12-dev

The installed version of LLVM will be used by default for out-of-tree build of the translator.

git clone https://github.com/KhronosGroup/SPIRV-LLVM-Translator.git
mkdir SPIRV-LLVM-Translator/build && cd SPIRV-LLVM-Translator/build
cmake ..
make llvm-spirv -j`nproc`

Build with pre-built LLVM

If you have a custom build (based on the latest version) of LLVM libraries you can link the translator against it.

git clone https://github.com/KhronosGroup/SPIRV-LLVM-Translator.git
mkdir SPIRV-LLVM-Translator/build && cd SPIRV-LLVM-Translator/build
cmake .. -DLLVM_DIR=<llvm_build_dir>/lib/cmake/llvm/
make llvm-spirv -j`nproc`

If the translator is used as part of another CMake project, you will need to define LLVM_SPIRV_BUILD_EXTERNAL:

cmake .. -DLLVM_DIR=<llvm_build_dir>/lib/cmake/llvm/ -DLLVM_SPIRV_BUILD_EXTERNAL=YES

Where llvm_build_dir is the LLVM build directory.

LLVM in-tree build

The translator can be built as a regular LLVM subproject. To do that you need to clone it into the llvm/projects or llvm/tools directory.

git clone https://github.com/llvm/llvm-project.git
cd llvm-project/llvm/projects
git clone https://github.com/KhronosGroup/SPIRV-LLVM-Translator.git

Run (or re-run) cmake as usual for LLVM. After that you should have llvm-spirv and check-llvm-spirv targets available.

mkdir llvm-project/build && cd llvm-project/build
cmake ../llvm -DLLVM_ENABLE_PROJECTS="clang"
make llvm-spirv -j`nproc`

Note on enabling the clang project: there are tests in the translator that depend on clang binary, which makes clang a required dependency (search for LLVM_SPIRV_TEST_DEPS in test/CMakeLists.txt) for check-llvm-spirv target.

Building clang from sources takes time and resources and it can be avoided:

• if you are not interested in launching unit-tests for the translator after build, you can disable generation of test targets by passing -DLLVM_SPIRV_INCLUDE_TESTS=OFF option.
• if you are interested in launching unit-tests, but don't want to build clang you can pass -DSPIRV_SKIP_CLANG_BUILD cmake option to avoid adding clang as dependency for check-llvm-spirv target. However, LIT will search for clang binary when tests are launched and it should be available at this point.
• building and testing completely without clang is not supported at the moment, see KhronosGroup/SPIRV-LLVM-Translator#477 to track progress, discuss and contribute.

Test instructions

All tests related to the translator are placed in the test directory. A number of the tests require spirv-as (part of SPIR-V Tools) to run, but the remainder of the tests can still be run without this. Optionally the tests can make use of spirv-val (part of SPIRV-Tools) in order to validate the generated SPIR-V against the official SPIR-V specification.

In case tests are failing due to SPIRV-Tools not supporting certain SPIR-V features, please get an updated package. The PKG_CONFIG_PATH environmental variable can be used to let cmake point to a custom installation.

Execute the following command inside the build directory to run translator tests:

make test

This requires that the -DLLVM_SPIRV_INCLUDE_TESTS=ON argument is passed to CMake during the build step. Additionally, -DLLVM_EXTERNAL_LIT="/usr/lib/llvm-12/build/utils/lit/lit.py" is needed when building with a pre-installed version of LLVM.

The translator test suite can be disabled by passing -DLLVM_SPIRV_INCLUDE_TESTS=OFF to CMake.

Run Instructions for llvm-spirv

To translate between LLVM IR and SPIR-V:

1. Execute the following command to translate input.bc to input.spv

   llvm-spirv input.bc
   

2. Execute the following command to translate input.spv to input.bc

   llvm-spirv -r input.spv
   

   Recommended options:

   • -spirv-ocl-builtins-version - to specify target version of OpenCL builtins to translate to (default CL1.2)

3. Other options accepted by llvm-spirv

   • -o file_name - to specify output name
   • -spirv-debug - output debugging information
   • -spirv-text - read/write SPIR-V in an internal textual format for debugging purpose. The textual format is not defined by SPIR-V spec.
   • -help - to see full list of options

Translation from LLVM IR to SPIR-V and then back to LLVM IR is not guaranteed to produce the original LLVM IR. In particular, LLVM intrinsic call instructions may get replaced by function calls to OpenCL builtins and metadata may be dropped.

Handling SPIR-V versions generated by the translator

There is one option to control the behavior of the translator with respect to the version of the SPIR-V file which is being generated/consumed.

• -spirv-max-version= - this option allows restricting the SPIRV-LLVM-Translator not to generate a SPIR-V with a version which is higher than the one specified via this option.

  If the -r option was also specified, the SPIRV-LLVM-Translator will reject the input file and emit an error if the SPIR-V version in it is higher than one specified via this option.

Allowed values are 1.0/1.1.

More information can be found in SPIR-V versions and extensions handling

Handling SPIR-V extensions generated by the translator

By default, during SPIR-V generation, the translator doesn't use any extensions. However, during SPIR-V consumption, the translator accepts input files that use any known extensions.

If certain extensions are required to be enabled or disabled, the following command line option can be used:

• --spirv-ext= - this options allows controlling which extensions are allowed/disallowed

Valid value for this option is comma-separated list of extension names prefixed with + or - - plus means allow to use extension, minus means disallow to use extension. There is one more special value which can be used as extension name in this option: all - it affects all extension which are known to the translator.

If --spirv-ext contains the name of an extension which is not known for the translator, it will emit an error.

More information can be found in SPIR-V versions and extensions handling

Branching strategy

Code on the master branch in this repository is intended to be compatible with the master branch of the llvm project. That is, for an OpenCL kernel compiled to llvm bitcode by the latest git revision of Clang it should be possible to translate it to SPIR-V with the llvm-spirv tool.

All new development should be done on the master branch.

To have versions compatible with released versions of LLVM and Clang, corresponding tags are available in this repository. For example, to build the translator with LLVM 7.0.0 one should use the v7.0.0-1 tag. The 7.x releases are maintained on the llvm_release_70 branch. As a general rule, commits from the master branch may be backported to the release branches as long as they do not depend on features from a later LLVM/Clang release and there are no objections from the maintainer(s). There is no guarantee that older release branches are proactively kept up to date with master, but you can request specific commits on older release branches by creating a pull request or raising an issue on GitHub.