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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
Change-Id: I68a38b8b8c1480e3b73d8e6f24e9dafece2c7de6
This commit is contained in:
Googler 2019-08-27 03:33:31 -07:00 committed by Copybara-Service
parent c2790137ae
commit ea5c5422a6
1 changed files with 64 additions and 0 deletions
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64
cc/private/toolchain/unix_cc_toolchain_config.bzl
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@ -1019,6 +1019,69 @@ def _impl(ctx):
],
)
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 @@ def _impl(ctx):
fdo_instrument_feature,
cs_fdo_instrument_feature,
cs_fdo_optimize_feature,
thinlto_feature,
fdo_prefetch_hints_feature,
autofdo_feature,
build_interface_libraries_feature,