Merge pull request redpanda-data#24373 from redpanda-data/stephan/baz…

…el-lto

bazel: Enable LTO for redpanda

.bazelrc

@@ -89,8 +89,9 @@ build:secure --config=relro
 build:release --compilation_mode opt
 build:release --config=secure
 build:release --copt -mllvm --copt -inline-threshold=2500
-build:release --linkopt=-flto
 build:release --@seastar//:stack_guards=False
+build:release --//src/v/redpanda:lto=True
+build:release --copt -flto=thin --copt -ffat-lto-objects
 
 build:stamp --stamp --workspace_status_command=./bazel/stamp_vars.sh
 

bazel/build.bzl

@@ -51,6 +51,7 @@ def redpanda_cc_binary(
         local_defines = [],
         visibility = None,
         copts = [],
+        linkopts = [],
         deps = []):
     """
     Define a Redpanda C++ binary.
@@ -64,6 +65,7 @@ def redpanda_cc_binary(
         visibility = visibility,
         deps = deps,
         copts = redpanda_copts() + copts,
+        linkopts = linkopts,
         features = [
             "layering_check",
         ],

bazel/thirdparty/krb5.BUILD

@@ -48,6 +48,10 @@ configure_make(
         "--disable-static",
         "--enable-asan=$(SANITIZERS)",
     ],
+    # Need to pass this additionally here because of a bug in the kerberos build where it doesn't properly pass the linker flag down
+    copts = [
+        "-fuse-ld=lld",
+    ],
     env = {
         "KRB5_BUILD_JOBS": "$(BUILD_JOBS)",
     },

src/v/redpanda/BUILD

@@ -1,3 +1,4 @@
+load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
 load("//bazel:build.bzl", "redpanda_cc_binary", "redpanda_cc_library")
 
 redpanda_cc_library(
@@ -95,11 +96,34 @@ redpanda_cc_library(
     ],
 )
 
+# Enable or disable (thin) LTO for the redpanda binary (only)
+bool_flag(
+    name = "lto",
+    build_setting_default = False,
+)
+
+config_setting(
+    name = "use_lto",
+    flag_values = {
+        ":lto": "true",
+    },
+    visibility = ["//visibility:public"],
+)
+
 redpanda_cc_binary(
     name = "redpanda",
     srcs = [
         "main.cc",
     ],
+    linkopts =
+        select({
+            ":use_lto": [
+                "-flto=thin",
+                "-ffat-lto-objects",
+            ],
+            "//conditions:default": [
+            ],
+        }),
     visibility = ["//visibility:public"],
     deps = [
         ":application",