Hello World with compiler optimization

Each binary target can have its own compiler options, and these can be customised differently for different optimisation levels. This takes three steps:

1. In your root folder BUILD.bazel, add the following entry:

config_setting(
    name = "release",
    values = {
        "compilation_mode": "opt",
    },
)

2. Add config option in .bazelrc to enable LTO together with optimized build.

common:opt --compilation_mode=opt
common:opt --@rules_rust//rust/settings:lto=thin

3. In your binary target, add the optimization flags & strip settings prefixed with -C. For a complete list of Rust compiler optimization flag, please read the official cargo documentation.

load("@rules_rust//rust:defs.bzl", "rust_binary")

rust_binary(
    name = "bin",
    srcs = ["src/main.rs"],
    deps = [],
    rustc_flags = select({
       "//:release": [
            "-Ccodegen-units=1",
            "-Cpanic=abort",
            "-Copt-level=3",
            "-Cstrip=symbols",
            ],
        "//conditions:default":
        [
           "-Copt-level=0",
        ],
    }),
    visibility = ["//visibility:public"],
)

Build with optimization:

bazel build --config opt //...

And run the optimized binary:

bazel run --config opt //...