Update hello_comp_opt example with new LTO settings (#3155)

Fixes comment mentioned in [3143#issuecomment-2568947858](#3143 (comment)) --------- Co-authored-by: UebelAndre <[email protected]>
bazelbuild · Jan 3, 2025 · b9f51f5 · b9f51f5
1 parent 568bb7b
commit b9f51f5
Show file tree

Hide file tree

Showing 4 changed files with 20 additions and 11 deletions.
diff --git a/examples/compile_opt/.bazelrc b/examples/compile_opt/.bazelrc
@@ -11,3 +11,7 @@ build --incompatible_merge_fixed_and_default_shell_env
 
 # https://github.com/bazelbuild/bazel/issues/23043.
 build --incompatible_autoload_externally=
+
+# in optimized build we will use thin lto
+common:opt -c opt
+common:opt --@rules_rust//rust/settings:lto=thin
diff --git a/examples/compile_opt/MODULE.bazel b/examples/compile_opt/MODULE.bazel
@@ -7,7 +7,7 @@ module(
 # B A Z E L  C E N T R A L  R E G I S T R Y # https://registry.bazel.build/
 ###############################################################################
 # https://github.com/bazelbuild/rules_rust/releases
-bazel_dep(name = "rules_rust", version = "0.46.0")
+bazel_dep(name = "rules_rust", version = "0.56.0")
 local_path_override(
     module_name = "rules_rust",
     path = "../..",
@@ -20,7 +20,7 @@ local_path_override(
 # Rust toolchain
 RUST_EDITION = "2021"
 
-RUST_VERSION = "1.79.0"
+RUST_VERSION = "1.83.0"
 
 rust = use_extension("@rules_rust//rust:extensions.bzl", "rust")
 rust.toolchain(

diff --git a/examples/compile_opt/README.md b/examples/compile_opt/README.md
@@ -3,7 +3,7 @@
 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:
+1) In your root folder `BUILD.bazel`, add the following entry:
 
 ```Starlark
 config_setting(
@@ -14,11 +14,18 @@ config_setting(
 )
 ```
 
-2) 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](https://doc.rust-lang.org/cargo/reference/profiles.html). 
+2) Add config option in `.bazelrc` to enable LTO together with optimized build.
 
-```Starlark 
+```Starlark
+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](https://doc.rust-lang.org/cargo/reference/profiles.html).
+
+```Starlark
 load("@rules_rust//rust:defs.bzl", "rust_binary")
 
 rust_binary(
@@ -27,7 +34,6 @@ rust_binary(
     deps = [],
     rustc_flags = select({
        "//:release": [
-            "-Clto=true",
             "-Ccodegen-units=1",
             "-Cpanic=abort",
             "-Copt-level=3",
@@ -44,8 +50,8 @@ rust_binary(
 
 Build with optimization:
 
-`bazel build -c opt //...`
+`bazel build --config opt //...`
 
 And run the optimized binary:
 
-`bazel run -c opt //...`
+`bazel run --config opt //...`
diff --git a/examples/compile_opt/hello_comp_opt/BUILD.bazel b/examples/compile_opt/hello_comp_opt/BUILD.bazel
@@ -5,7 +5,6 @@ rust_binary(
     srcs = ["src/main.rs"],
     rustc_flags = select({
         "//:release": [
-            "-Clto",
             "-Ccodegen-units=1",
             "-Cpanic=abort",
             "-Copt-level=3",