IDE Configuration

VS Code

For an out-of-tree MLIR project built with Bazel, install the following VS Code extensions:

• llvm-vs-code-extensions.vscode-mlir: Adds language support for MLIR, PDLL, and TableGen.
• llvm-vs-code-extensions.vscode-clangd: Adds clangd code completion using a generated compile_commands.json file.
• bazelbuild.vscode-bazel: Support for Bazel.

You will also need to disable ms-vscode.cpptools to avoid a conflict with clangd.

Add the following snippet to your VS Code user settings found in .vscode/settings.json to enable autocomplete based on the compile_commands.json file.

   "clangd.arguments": [
        "--compile-commands-dir=${workspaceFolder}/",
        "--completion-style=detailed",
        "--query-driver=**"
      ],

To generate the compile_commands.json file, run

bazel run @hedron_compile_commands//:refresh_all

This will need to be regenerated every time you want tooling to see new BUILD file changes.

If you encounter errors like *.h.inc not found, or syntax errors inside these files, you may need to build those targets and then re-run the refresh_all command above.

Tips for working with Bazel

Bazel is notoriously fickle when it comes to deciding whether a full rebuild is necessary, which is bad for HEIR because rebuilding LLVM from scratch takes 15 minutes or more.

The main things that cause a rebuild are:

• A change to the command-line flags passed to bazel, e.g., -c opt vs -c dbg for optimization level and debug symbols.
• A change to the .bazelrc that implicitly causes a flag change. Note HEIR has its own project-specific .bazelrc in the root directory.
• A change to relevant command-line variables, such as PATH, which is avoided by the incompatible_strict_action_env flag. Note activating a python virtualenv triggers a PATH change.

Bazel compilation flags are set by default in the project root’s .bazelrc in such a way as to avoid rebuilds during development as much as possible. This includes setting -c dbg and --incompatible_strict_action_env.