Add support for thin LTO optimization in Bazel
Usage: CC=clang bazel build //foo:bar --features=thin_lto -c opt
RELNOTES: Bazel now supports ThinLTO builds on Linux for Clang versions >= 6.0. ThinLTO can be enabled through --features=thin_lto
PiperOrigin-RevId: 265649618
diff --git a/tools/cpp/unix_cc_toolchain_config.bzl b/tools/cpp/unix_cc_toolchain_config.bzl
index bf4d8394..c5fd79e 100644
--- a/tools/cpp/unix_cc_toolchain_config.bzl
+++ b/tools/cpp/unix_cc_toolchain_config.bzl
@@ -1019,6 +1019,69 @@
],
)
+ thinlto_feature = feature(
+ name = "thin_lto",
+ flag_sets = [
+ flag_set(
+ actions = [
+ ACTION_NAMES.c_compile,
+ ACTION_NAMES.cpp_compile,
+ ] + all_link_actions + lto_index_actions,
+ flag_groups = [
+ flag_group(flags = ["-flto=thin"]),
+ flag_group(
+ expand_if_available = "lto_indexing_bitcode_file",
+ flags = [
+ "-Xclang",
+ "-fthin-link-bitcode=%{lto_indexing_bitcode_file}",
+ ],
+ ),
+ ],
+ ),
+ flag_set(
+ actions = [ACTION_NAMES.linkstamp_compile],
+ flag_groups = [flag_group(flags = ["-DBUILD_LTO_TYPE=thin"])],
+ ),
+ flag_set(
+ actions = lto_index_actions,
+ flag_groups = [
+ flag_group(flags = [
+ "-flto=thin",
+ "-Wl,-plugin-opt,thinlto-index-only%{thinlto_optional_params_file}",
+ "-Wl,-plugin-opt,thinlto-emit-imports-files",
+ "-Wl,-plugin-opt,thinlto-prefix-replace=%{thinlto_prefix_replace}",
+ ]),
+ flag_group(
+ expand_if_available = "thinlto_object_suffix_replace",
+ flags = [
+ "-Wl,-plugin-opt,thinlto-object-suffix-replace=%{thinlto_object_suffix_replace}",
+ ],
+ ),
+ flag_group(
+ expand_if_available = "thinlto_merged_object_file",
+ flags = [
+ "-Wl,-plugin-opt,obj-path=%{thinlto_merged_object_file}",
+ ],
+ ),
+ ],
+ ),
+ flag_set(
+ actions = [ACTION_NAMES.lto_backend],
+ flag_groups = [
+ flag_group(flags = [
+ "-c",
+ "-fthinlto-index=%{thinlto_index}",
+ "-o",
+ "%{thinlto_output_object_file}",
+ "-x",
+ "ir",
+ "%{thinlto_input_bitcode_file}",
+ ]),
+ ],
+ ),
+ ],
+ )
+
is_linux = ctx.attr.target_libc != "macosx"
# TODO(#8303): Mac crosstool should also declare every feature.
@@ -1034,6 +1097,7 @@
fdo_instrument_feature,
cs_fdo_instrument_feature,
cs_fdo_optimize_feature,
+ thinlto_feature,
fdo_prefetch_hints_feature,
autofdo_feature,
build_interface_libraries_feature,
