Build faster

TL;DR

For local developing workflow, build with --config=fast.

Example:

$ tools/bazel run --config=fast //common:kernel_aarch64 -- --dist_dir=out/dist

Or add to user.bazelrc:

# user.bazelrc
build --config=fast

How does this work?

This config implies:

• --lto=thin. See LTO.
• --config=local. See sandbox.md.

LTO

By default, --config=fast implies --lto=thin. If you want to specify otherwise, you may override its value in user.bazelrc, e.g.

# user.bazelrc

# When `--config=fast` is set, disable LTO
build:fast --lto=none

# When no config is set, disable LTO
build --lto=none

NOTE: If you are using --lto with --config=fast, --lto must be specified after --config=fast because flags specified later take precedence. If unsure, use --config=local instead. For example:

# CORRECT:
$ tools/bazel run --config=fast --lto=none //common:kernel_dist

# CORRECT:
$ tools/bazel run --config=local --lto=none //common:kernel_dist

# WRONG: --lto is set to thin
# tools/bazel run --lto=none --config=fast //common:kernel_dist

You may build the following to confirm the value of LTO setting:

$ tools/bazel build [flags] //build/kernel/kleaf:print_flags