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bazel: Add pre-compiled clang header poc (#13788)
* bazel: Add pre-compiled clang header poc This adds a custom rule for producing clang pre-compiled headers. The hope is that by using these we reduce significant duplication in some larger headers that get recompiled by many dependees. This works by fetching the normal C++ configuration from bazel's crosstool, and adding custom flags to compile our pch in the right mode. This currently has a few limitations / rough edges: 1. It only supports clang 2. There's no way with the CcInfo provider to propagate compiler flags up the dependency tree. Because of this we instead add the required `-include-pch` flag to all macros. 3. Pch files are timestamp sensitive, this means if you add a include to the pch, build, then remove it and rebuild, it will currently fail. LLVM master has a flag to ignore this timestamp, but it isn't currently available in the release version of Xcode on macOS. 4. The logic to disable isn't implemented yet. Signed-off-by: Keith Smiley <keithbsmiley@gmail.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,51 @@ | ||
| load("@rules_cc//cc:defs.bzl", "cc_library") | ||
|
|
||
| # DO NOT LOAD THIS FILE. Load envoy_build_system.bzl instead. | ||
| # Envoy library targets | ||
| load( | ||
| ":envoy_internal.bzl", | ||
| "envoy_copts", | ||
| "envoy_external_dep_path", | ||
| "envoy_linkstatic", | ||
| ) | ||
| load(":pch.bzl", "pch") | ||
|
|
||
| def envoy_pch_copts(repository, target): | ||
| return select({ | ||
| repository + "//bazel:clang_pch_build": [ | ||
| "-include-pch", | ||
| "$(location {}{})".format(repository, target), | ||
| ], | ||
| "//conditions:default": [], | ||
| }) | ||
|
|
||
| def envoy_pch_library( | ||
| name, | ||
| includes, | ||
| deps, | ||
| external_deps, | ||
| visibility, | ||
| testonly = False, | ||
| repository = ""): | ||
| cc_library( | ||
| name = name + "_libs", | ||
| visibility = ["//visibility:private"], | ||
| copts = envoy_copts(repository), | ||
| deps = deps + [envoy_external_dep_path(dep) for dep in external_deps], | ||
| alwayslink = 1, | ||
| testonly = testonly, | ||
| linkstatic = envoy_linkstatic(), | ||
| ) | ||
|
|
||
| pch( | ||
| name = name, | ||
| deps = [name + "_libs"], | ||
| includes = includes, | ||
| visibility = visibility, | ||
| testonly = testonly, | ||
| tags = ["no-remote"], | ||
| enabled = select({ | ||
| repository + "//bazel:clang_pch_build": True, | ||
| "//conditions:default": False, | ||
| }), | ||
| ) |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,114 @@ | ||
| load( | ||
| "@bazel_tools//tools/build_defs/cc:action_names.bzl", | ||
| "CPP_COMPILE_ACTION_NAME", | ||
| ) | ||
|
|
||
| def _pch(ctx): | ||
| deps_cc_info = cc_common.merge_cc_infos( | ||
| cc_infos = [dep[CcInfo] for dep in ctx.attr.deps], | ||
| ) | ||
|
|
||
| if not ctx.attr.enabled: | ||
| return [deps_cc_info] | ||
|
|
||
| cc_toolchain = ctx.attr._cc_toolchain[cc_common.CcToolchainInfo] | ||
| feature_configuration = cc_common.configure_features( | ||
| ctx = ctx, | ||
| cc_toolchain = cc_toolchain, | ||
| requested_features = ctx.features, | ||
| unsupported_features = ctx.disabled_features, | ||
| ) | ||
|
|
||
| cc_compiler_path = cc_common.get_tool_for_action( | ||
| feature_configuration = feature_configuration, | ||
| action_name = CPP_COMPILE_ACTION_NAME, | ||
| ) | ||
|
|
||
| if "clang" not in cc_compiler_path: | ||
| fail("error: attempting to use clang PCH without clang: {}".format(cc_compiler_path)) | ||
|
|
||
| generated_header_file = ctx.actions.declare_file(ctx.label.name + ".h") | ||
| ctx.actions.write( | ||
| generated_header_file, | ||
| "\n".join(["#include \"{}\"".format(include) for include in ctx.attr.includes]) + "\n", | ||
| ) | ||
|
|
||
| # TODO: -fno-pch-timestamp / invalidation in that case doesn't work | ||
| pch_flags = ["-x", "c++-header"] | ||
| pch_file = ctx.actions.declare_file(ctx.label.name + ".pch") | ||
|
|
||
| deps_ctx = deps_cc_info.compilation_context | ||
| cc_compile_variables = cc_common.create_compile_variables( | ||
| feature_configuration = feature_configuration, | ||
| cc_toolchain = cc_toolchain, | ||
| user_compile_flags = ctx.fragments.cpp.copts + ctx.fragments.cpp.cxxopts + pch_flags, | ||
| source_file = generated_header_file.path, | ||
| output_file = pch_file.path, | ||
| preprocessor_defines = depset(deps_ctx.defines.to_list() + deps_ctx.local_defines.to_list()), | ||
| include_directories = deps_ctx.includes, | ||
| quote_include_directories = deps_ctx.quote_includes, | ||
| system_include_directories = deps_ctx.system_includes, | ||
| framework_include_directories = deps_ctx.framework_includes, | ||
| ) | ||
|
|
||
| env = cc_common.get_environment_variables( | ||
| feature_configuration = feature_configuration, | ||
| action_name = CPP_COMPILE_ACTION_NAME, | ||
| variables = cc_compile_variables, | ||
| ) | ||
|
|
||
| command_line = cc_common.get_memory_inefficient_command_line( | ||
| feature_configuration = feature_configuration, | ||
| action_name = CPP_COMPILE_ACTION_NAME, | ||
| variables = cc_compile_variables, | ||
| ) | ||
|
|
||
| transitive_headers = [] | ||
| for dep in ctx.attr.deps: | ||
| transitive_headers.append(dep[CcInfo].compilation_context.headers) | ||
| ctx.actions.run( | ||
| executable = cc_compiler_path, | ||
| arguments = command_line, | ||
| env = env, | ||
| inputs = depset( | ||
| items = [generated_header_file], | ||
| transitive = [cc_toolchain.all_files] + transitive_headers, | ||
| ), | ||
| outputs = [pch_file], | ||
| ) | ||
|
|
||
| return [ | ||
| DefaultInfo(files = depset(items = [pch_file])), | ||
| cc_common.merge_cc_infos( | ||
| direct_cc_infos = [ | ||
| CcInfo( | ||
| compilation_context = cc_common.create_compilation_context( | ||
| headers = depset([pch_file, generated_header_file]), | ||
| ), | ||
| ), | ||
| ], | ||
| cc_infos = [deps_cc_info], | ||
| ), | ||
| ] | ||
|
|
||
| pch = rule( | ||
| attrs = dict( | ||
| includes = attr.string_list( | ||
| mandatory = True, | ||
| allow_empty = False, | ||
| ), | ||
| deps = attr.label_list( | ||
| mandatory = True, | ||
| allow_empty = False, | ||
| providers = [CcInfo], | ||
| ), | ||
| enabled = attr.bool( | ||
| mandatory = True, | ||
| ), | ||
| _cc_toolchain = attr.label(default = Label("@bazel_tools//tools/cpp:current_cc_toolchain")), | ||
| ), | ||
| fragments = ["cpp"], | ||
| provides = [CcInfo], | ||
| toolchains = ["@bazel_tools//tools/cpp:toolchain_type"], | ||
| implementation = _pch, | ||
| ) |
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