a45e58af1b
This commit adds the `BufferViewFlowOpInterface` to the bufferization dialect. This interface can be implemented by ops that operate on buffers to indicate that a buffer op result and/or region entry block argument may be the same buffer as a buffer operand (or a view thereof). This interface is queried by the `BufferViewFlowAnalysis`. The new interface has two interface methods: * `populateDependencies`: Implementations use the provided callback to declare dependencies between operands and op results/region entry block arguments. E.g., for `%r = arith.select %c, %m1, %m2 : memref<5xf32>`, the interface implementation should declare two dependencies: %m1 -> %r and %m2 -> %r. * `mayBeTerminalBuffer`: An SSA value is a terminal buffer if the buffer view flow analysis stops at the specified value. E.g., because the value is a newly allocated buffer or because no further information is available about the origin of the buffer. Ops that implement the `RegionBranchOpInterface` or `BranchOpInterface` do not have to implement the `BufferViewFlowOpInterface`. The buffer dependencies can be inferred from those two interfaces. This commit makes the `BufferViewFlowAnalysis` more accurate. For unknown ops, it conservatively used to declare all combinations of operands and op results/region entry block arguments as dependencies (false positives). This is no longer the case. While the analysis is still a "maybe" analysis with false positives (e.g., when analyzing ops such as `arith.select` or `scf.if` where the taken branch is not known at compile time), results and region entry block arguments of unknown ops are now marked as terminal buffers. This commit addresses a TODO in `BufferViewFlowAnalysis.cpp`: ``` // TODO: We should have an op interface instead of a hard-coded list of // interfaces/ops. ``` It is no longer needed to hard-code ops.
Introduction
Warning The Bazel build is experimental and best-effort, supported in line with the policy for LLVM's peripheral support tier. LLVM's official build system is CMake. If in doubt use that. If you make changes to LLVM, you're expected to update the CMake build but you don't need to update Bazel build files. Reviewers should not ask authors to update Bazel build files unless the author has opted in to support Bazel. Keeping the Bazel build files up-to-date is on the people who use the Bazel build.
Bazel is a multi-language build system focused on reproducible builds to enable dependency analysis and caching for fast incremental builds.
The main motivation behind the existence of an LLVM Bazel build is that a number of projects that depend on LLVM use Bazel, and Bazel works best when it knows about the whole source tree (as opposed to installing artifacts coming from another build system). Community members are also welcome to use Bazel for their own development as long as they continue to maintain the official CMake build system. See also, the proposal for adding this configuration.
Quick Start
git clone https://github.com/llvm/llvm-project.git; cd llvm-projectif you don't have a checkout yet.- Install Bazel at the version indicated by .bazelversion,
following the official instructions, if you don't have it installed yet:
https://docs.bazel.build/versions/main/install.html.
- You can also install and use bazelisk which automates downloading the proper bazel version
cd utils/bazelbazel build --config=generic_clang @llvm-project//...- If you're using clang, it's expected that lld is also available
- If you're using MSVC or gcc, instead of
--config=generic_clang, pass--config=generic_gccor--config=msvc - To specify a specific local compiler to use, add the following bazel
flag:
--repo_env=CC=/usr/bin/clang--config=generic_clang/--config=generic_gccby default set--repo_env=CC=clang/--repo_env=CC=gcc, usingclang/gccon thePATH
Configuration
The repository .bazelrc will import user-specific settings from a
user.bazelrc file (in addition to the standard locations). Adding your typical
config setting is recommended.
build --config=generic_clang
You can enable disk caching, which will cache build results
build --disk_cache=~/.cache/bazel-disk-cache
You can instruct Bazel to use a ramdisk for its sandboxing operations via --sandbox_base, which can help avoid IO bottlenecks for the symlink strategy used for sandboxing. This is especially important with many inputs and many cores (see https://github.com/bazelbuild/bazel/issues/11868):
build --sandbox_base=/dev/shm
Bear in mind that this requires that your ramdisk is of sufficient size to hold any temporary files. Anecdotally, 1GB should be sufficient.
Coverage
The LLVM, MLIR, and Clang subprojects have configurations for Linux (Clang and GCC), Mac (Clang and GCC), and Windows (MSVC). Configuration options that are platform-specific are selected for in defines. Many are also hardcoded to the values currently used by all supported configurations. If there is a configuration you'd like to use that isn't supported, please send a patch.
Continuous Testing
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Pre-merge Testing
A Buildkite pipeline runs the full Bazel build as a pre-merge test using the LLVM pre-merge testing. It is triggered on all changes to the utils/bazel directory and when the patch author is a member of the Bazel Phabricator project. If you use or benefit from the Bazel build, please join the project so that you can help keep it green. As a bonus, it runs in under 5 minutes, much faster than any of the other pre-merge builds.
Usage in Downstream Projects
To use in dependent projects using Bazel, you can import LLVM and then use the
provided configuration rule. See example usage in the examples/ directory.