How to diagnose Bazel build performance using measurements and profiling

To diagnose Bazel performance, follow these steps:

1. Enable profiling with bazel build //... --profile=profile.out to capture timing data.
2. Examine the generated profile using bazel analyze-profile profile.out or view it in the Bazel UI.
3. Identify long‑running actions (e.g., compilation, linking) and check their input sizes and dependencies.
4. Look for unnecessary rebuilds by reviewing --noprogess logs or using bazel query to see which targets changed.
5. Apply optimizations such as adding srcs reductions, enabling remote caching, or splitting large targets.
6. Re‑run the build to verify improvements; if regressions appear, revert the changes to BUILD files or flags.