llvm/utils/gn/build/BUILD.gn - llvm-project - Git at Google

 import("//llvm/utils/gn/build/buildflags.gni")
 import("//llvm/utils/gn/build/mac_sdk.gni")
 import("//llvm/utils/gn/build/sysroot.gni")
 import("//llvm/utils/gn/build/toolchain/compiler.gni")
 import("//llvm/utils/gn/build/toolchain/target_flags.gni")

 declare_args() {
   # Whether to build everything with coverage information.
   # After building with this, run tests and then run
   #    llvm/utils/prepare-code-coverage-artifact.py \
   #        --compilation-dir=out/gn \
   #        .../llvm-profdata .../llvm-cov out/gn/profiles/ report/ \
   #        out/gn/bin/llvm-undname ...
   # to generate a HTML report for the binaries passed in the last line.
   llvm_build_instrumented_coverage = false

   # If set, puts relative paths in debug info.
   # Makes the build output independent of the build directory, but makes
   # most debuggers harder to use. See "Getting to local determinism" and
   # "Getting debuggers to work well with locally deterministic builds" in
   # http://blog.llvm.org/2019/11/deterministic-builds-with-clang-and-lld.html
   # for more information.
   use_relative_paths_in_debug_info = false

   # The version of host gcc. Ignored if is_clang is true.
   gcc_version = 9
 }

 assert(!llvm_build_instrumented_coverage || is_clang,
        "llvm_build_instrumented_coverage requires clang as host compiler")

 config("compiler_defaults") {
   defines = []

   if (!llvm_enable_assertions) {
     defines += [ "NDEBUG" ]
   }

   if (llvm_enable_expensive_checks) {
     defines += [ "EXPENSIVE_CHECKS" ]
   }

   asmflags = target_flags
   cflags = target_flags
   cflags_cc = []
   ldflags = target_flags + target_ldflags

   # Mostly for compiler-rt, see compiler-rt/cmake/config-ix.cmake
   if (current_os == "ios") {
     asmflags += [ "-miphoneos-version-min=8.0" ]
     cflags += [ "-miphoneos-version-min=8.0" ]
     ldflags += [ "-miphoneos-version-min=8.0" ]
   }
   if (current_os == "mac") {
     asmflags += [ "-mmacosx-version-min=10.10" ]
     cflags += [ "-mmacosx-version-min=10.10" ]
     ldflags += [ "-mmacosx-version-min=10.10" ]
   }

   assert(symbol_level == 0 || symbol_level == 1 || symbol_level == 2,
          "Unexpected symbol_level")
   if (host_os != "win") {
     if (symbol_level == 2) {
       cflags += [ "-g" ]

       # For full debug-info -g builds, --gdb-index makes links ~15% slower, and
       # gdb symbol reading time 1500% faster (lld links in 4.4 instead of 3.9s,
       # and gdb loads and runs it in 2s instead of in 30s).  It's likely that
       # people doing symbol_level=2 want to run a debugger (since
       # symbol_level=2 isn't the default). So this seems like the right
       # tradeoff.
       if (host_os != "mac" && use_lld) {
         cflags += [ "-ggnu-pubnames" ]  # PR34820
         ldflags += [ "-Wl,--gdb-index" ]
       }
     } else if (symbol_level == 1) {
       cflags += [ "-g1" ]
       # For linetable-only -g1 builds, --gdb-index makes links ~8% slower, but
       # links are 4x faster than -g builds so it's a fairly small absolute cost.
       # On the other hand, gdb startup is well below 1s with and without the
       # index, and people using -g1 likely don't use a debugger. So don't use
       # the flag here.
     }
     if (is_optimized) {
       cflags += [ "-O3" ]
     }
     cflags += [ "-fdiagnostics-color" ]
     if (use_lld) {
       ldflags += [ "-Wl,--color-diagnostics" ]
     }
     cflags_cc += [
       "-std=c++14",
       "-fvisibility-inlines-hidden",
     ]
   } else {
     if (symbol_level != 0) {
       cflags += [
         "/Zi",
         "/FS",
       ]
       if (symbol_level == 1 && is_clang) {
         cflags += [ "-gline-tables-only" ]
       }
       ldflags += [ "/DEBUG" ]

       # Speed up links with ghash on windows.
       if (use_lld && is_clang) {
         cflags += [ "-gcodeview-ghash" ]
         ldflags += [ "/DEBUG:GHASH" ]
       }
     }
     if (is_optimized) {
       cflags += [
         "/O2",
         "/Gw",
         "/Zc:inline",
       ]
       ldflags += [
         "/OPT:REF",
         "/OPT:ICF",
       ]
     }
     defines += [
       "_CRT_SECURE_NO_DEPRECATE",
       "_CRT_SECURE_NO_WARNINGS",
       "_CRT_NONSTDC_NO_DEPRECATE",
       "_CRT_NONSTDC_NO_WARNINGS",
       "_SCL_SECURE_NO_DEPRECATE",
       "_SCL_SECURE_NO_WARNINGS",

       "_HAS_EXCEPTIONS=0",
       "_UNICODE",
       "UNICODE",
     ]
     cflags += [ "/EHs-c-" ]

     # The MSVC default value (1 MB) is not enough for parsing recursive C++
     # templates in Clang.
     ldflags += [ "/STACK:10000000" ]
   }

   # Warning setup.
   if (host_os == "win" && !is_clang) {
     cflags += [
       # Suppress ''modifier' : used more than once' (__forceinline and inline).
       "-wd4141",

       # Suppress 'conversion from 'type1' to 'type2', possible loss of data'.
       "-wd4244",

       # Suppress 'conversion from 'size_t' to 'type', possible loss of data'.
       "-wd4267",

       # Suppress 'no matching operator delete found'.
       "-wd4291",

       # Suppress 'noexcept used with no exception handling mode specified'.
       "-wd4577",

       # Suppress 'destructor was implicitly defined as deleted'.
       "-wd4624",

       # Suppress 'unsafe mix of type <type> and type <type> in operation'.
       "-wd4805",
     ]
   } else {
     if (host_os == "win") {
       cflags += [ "/W4" ]
     } else {
       cflags += [
         "-Wall",
         "-Wextra",
       ]
     }
     cflags += [ "-Wno-unused-parameter" ]
     if (is_clang) {
       cflags += [
         "-Wdelete-non-virtual-dtor",
         "-Wstring-conversion",
       ]
     } else {
       cflags += [
         # GCC's -Wcomment complains about // comments ending with '\' if the
         # next line is also a // comment.
         "-Wno-comment",

         # Disable gcc's potentially uninitialized use analysis as it presents
         # lots of false positives.
         "-Wno-maybe-uninitialized",
       ]
       cflags_cc += [
         # The LLVM libraries have no stable C++ API, so -Wnoexcept-type is not
         # useful.
         "-Wno-noexcept-type",
       ]
       if (gcc_version >= 8) {
         cflags_cc += [
           # Disable -Wclass-memaccess, a C++-only warning from GCC 8 that fires
           # on LLVM's ADT classes.
           "-Wno-class-memaccess",
         ]
       }
       if (gcc_version >= 9) {
         cflags_cc += [
           # Disable -Wredundant-move on GCC>=9. GCC wants to remove std::move
           # in code like "A foo(ConvertibleToA a) { return std::move(a); }",
           # but this code does not compile (or uses the copy constructor
           # instead) on clang<=3.8. Clang also has a -Wredundant-move, but it
           # only fires when the types match exactly, so we can keep it here.
           "-Wno-redundant-move",
         ]
       }
     }
     if (is_clang && use_goma) {
       # goma converts all paths to lowercase on the server, breaking this
       # warning.
       cflags += [ "-Wno-nonportable-include-path" ]
     }
   }

   # On Windows, the linker is not invoked through the compiler driver.
   if (use_lld && host_os != "win") {
     ldflags += [ "-fuse-ld=lld" ]
   }

   if (llvm_build_instrumented_coverage) {
     cflags += [
       "-fcoverage-mapping",

       # For build determinism. Using this requires passing --compilation-dir to
       # llvm/utils/prepare-code-coverage-artifact.py.
       "-fcoverage-compilation-dir=.",

       # Using an absolute path here is lame, but it's used at test execution
       # time to generate the profiles, and lit doesn't specify a fixed folder
       # for test execution -- so this is the only way to get all profiles into
       # a single folder like llvm/utils/prepare-code-coverage-artifact.py
       # expects.
       "-fprofile-instr-generate=" +
           rebase_path("$root_build_dir/profiles/%4m.profraw"),
     ]
     if (host_os != "win") {
       ldflags += [ "-fprofile-instr-generate" ]
     }
   }

   # Deterministic build setup, see
   # http://blog.llvm.org/2019/11/deterministic-builds-with-clang-and-lld.html
   if (current_os == "win") {
     ldflags += [ "/pdbaltpath:%_PDB%" ]
   }
   if (is_clang) {
     cflags += [
       "-no-canonical-prefixes",
       "-Werror=date-time",
     ]
     if (current_os == "win") {
       cflags += [ "-fmsc-version=1916" ]
       if (use_lld) {
         cflags += [ "/Brepro" ]
         ldflags += [ "/Brepro" ]
       }
     }
     if (use_relative_paths_in_debug_info) {
       cflags += [ "-fdebug-compilation-dir=." ]
     }
   }
   if (sysroot != "") {
     if (current_os == "win") {
       assert(is_clang, "sysroot only works with clang-cl as host compiler")
       cflags += [ "/winsysroot" + rebase_path(sysroot, root_build_dir) ]
     } else if (current_os != "ios" && current_os != "mac" &&
                current_os != "android") {
       cflags += [ "--sysroot=" + rebase_path(sysroot, root_build_dir) ]
     }
   }
   if ((current_os == "ios" || current_os == "mac") &&
       (clang_base_path != "" || sysroot != "")) {
     if (current_os == "ios" && current_cpu == "arm64") {
       sdk_path = ios_sdk_path
     } else if (current_os == "ios" && current_cpu == "x64") {
       sdk_path = iossim_sdk_path
     } else if (current_os == "mac") {
       sdk_path = mac_sdk_path
     }
     cflags += [
       "-isysroot",
       rebase_path(sdk_path, root_build_dir),
     ]
     ldflags += [
       "-isysroot",
       rebase_path(sdk_path, root_build_dir),
     ]
   }
   if (sysroot != "" && current_os != "win" && is_clang) {
     cflags += [ "-Wpoison-system-directories" ]
   }
   assert(
       !use_goma || sysroot != "",
       "goma needs a sysroot: run `llvm/utils/sysroot.py make-fake --out-dir=sysroot` and add `sysroot = \"//sysroot\"` to your args.gn")

   if (use_ubsan) {
     assert(is_clang && current_os == "linux",
            "ubsan only supported on Linux/Clang")
     cflags += [
       "-fsanitize=undefined",
       "-fno-sanitize-recover=all",
     ]
     ldflags += [ "-fsanitize=undefined" ]
   }

   if (use_asan) {
     assert(is_clang && (current_os == "ios" || current_os == "linux" ||
                             current_os == "mac"),
            "asan only supported on iOS/Clang, Linux/Clang, and macOS/Clang")
     cflags += [ "-fsanitize=address" ]
     ldflags += [ "-fsanitize=address" ]
   }

   if (use_tsan) {
     assert(is_clang && current_os == "linux",
            "tsan only supported on Linux/Clang")
     cflags += [ "-fsanitize=thread" ]
     ldflags += [ "-fsanitize=thread" ]
   }

   if (use_thinlto) {
     assert(is_clang, "ThinLTO only supported on Clang")

     lto_opt_level = 2

     cflags += [ "-flto=thin" ]

     if (host_os == "win") {
       ldflags += [
         "/opt:lldlto=" + lto_opt_level,
         "/opt:lldltojobs=" + max_jobs_per_lto_link,
       ]
     } else {
       ldflags += [
         "-flto=thin",
         "-Wl,--thinlto-jobs=" + max_jobs_per_lto_link,
         "-Wl,--lto-O" + lto_opt_level,
       ]
     }
   }

   cflags_objcc = cflags_cc
 }

 config("no_exceptions") {
   cflags_cc = []
   if (host_os != "win") {
     cflags_cc += [ "-fno-exceptions" ]
   }
   cflags_objcc = cflags_cc
 }

 config("no_rtti") {
   if (current_os == "win") {
     cflags_cc = [ "/GR-" ]
   } else {
     cflags_cc = [ "-fno-rtti" ]
   }
   cflags_objcc = cflags_cc
 }

 config("zdefs") {
   # -Wl,-z,defs doesn't work with sanitizers.
   # https://clang.llvm.org/docs/AddressSanitizer.html
   if (current_os != "ios" && current_os != "mac" && current_os != "win" &&
       !(use_asan || use_tsan || use_ubsan)) {
     ldflags = [ "-Wl,-z,defs" ]
   }
 }

 # To make an archive that can be distributed, you need to remove this config and
 # set complete_static_lib.
 config("thin_archive") {
   if (current_os != "ios" && current_os != "mac" && current_os != "win") {
     arflags = [ "-T" ]
   }
 }

 config("llvm_code") {
   include_dirs = [
     "//llvm/include",
     "$root_gen_dir/llvm/include",
   ]
   if (current_os != "win") {
     cflags = [ "-fPIC" ]
   }
 }

 config("lld_code") {
   include_dirs = [
     "//lld/include",
     "$root_gen_dir/lld/include",
   ]
 }

 config("clang_code") {
   if (host_os != "win") {
     cflags = [ "-fno-strict-aliasing" ]
   }
   include_dirs = [
     "//clang/include",
     "$root_gen_dir/clang/include",
   ]
 }

 config("crt_code") {
   include_dirs = [ "//compiler-rt/lib" ]
   cflags = [
     "-fPIC",
     "-funwind-tables",
     "-gline-tables-only",
     "-fvisibility=hidden",
   ]
   if (is_clang) {
     cflags += [
       "-Werror=thread-safety",
       "-Werror=thread-safety-reference",
       "-Werror=thread-safety-beta",
     ]
   }
 }

 config("lldb_code") {
   if (host_os != "win") {
     cflags = [ "-fno-strict-aliasing" ]
   }
   include_dirs = [
     "//lldb/include",
     "$root_gen_dir/lldb/include",
   ]
 }

 config("warn_covered_switch_default") {
   if (is_clang) {
     cflags = [ "-Wcovered-switch-default" ]
   }
 }
	import("//llvm/utils/gn/build/buildflags.gni")
	import("//llvm/utils/gn/build/mac_sdk.gni")
	import("//llvm/utils/gn/build/sysroot.gni")
	import("//llvm/utils/gn/build/toolchain/compiler.gni")
	import("//llvm/utils/gn/build/toolchain/target_flags.gni")

	declare_args() {
	# Whether to build everything with coverage information.
	# After building with this, run tests and then run
	# llvm/utils/prepare-code-coverage-artifact.py \
	# --compilation-dir=out/gn \
	# .../llvm-profdata .../llvm-cov out/gn/profiles/ report/ \
	# out/gn/bin/llvm-undname ...
	# to generate a HTML report for the binaries passed in the last line.
	llvm_build_instrumented_coverage = false

	# If set, puts relative paths in debug info.
	# Makes the build output independent of the build directory, but makes
	# most debuggers harder to use. See "Getting to local determinism" and
	# "Getting debuggers to work well with locally deterministic builds" in
	# http://blog.llvm.org/2019/11/deterministic-builds-with-clang-and-lld.html
	# for more information.
	use_relative_paths_in_debug_info = false

	# The version of host gcc. Ignored if is_clang is true.
	gcc_version = 9
	}

	assert(!llvm_build_instrumented_coverage \|\| is_clang,
	"llvm_build_instrumented_coverage requires clang as host compiler")

	config("compiler_defaults") {
	defines = []

	if (!llvm_enable_assertions) {
	defines += [ "NDEBUG" ]
	}

	if (llvm_enable_expensive_checks) {
	defines += [ "EXPENSIVE_CHECKS" ]
	}

	asmflags = target_flags
	cflags = target_flags
	cflags_cc = []
	ldflags = target_flags + target_ldflags

	# Mostly for compiler-rt, see compiler-rt/cmake/config-ix.cmake
	if (current_os == "ios") {
	asmflags += [ "-miphoneos-version-min=8.0" ]
	cflags += [ "-miphoneos-version-min=8.0" ]
	ldflags += [ "-miphoneos-version-min=8.0" ]
	}
	if (current_os == "mac") {
	asmflags += [ "-mmacosx-version-min=10.10" ]
	cflags += [ "-mmacosx-version-min=10.10" ]
	ldflags += [ "-mmacosx-version-min=10.10" ]
	}

	assert(symbol_level == 0 \|\| symbol_level == 1 \|\| symbol_level == 2,
	"Unexpected symbol_level")
	if (host_os != "win") {
	if (symbol_level == 2) {
	cflags += [ "-g" ]

	# For full debug-info -g builds, --gdb-index makes links ~15% slower, and
	# gdb symbol reading time 1500% faster (lld links in 4.4 instead of 3.9s,
	# and gdb loads and runs it in 2s instead of in 30s). It's likely that
	# people doing symbol_level=2 want to run a debugger (since
	# symbol_level=2 isn't the default). So this seems like the right
	# tradeoff.
	if (host_os != "mac" && use_lld) {
	cflags += [ "-ggnu-pubnames" ] # PR34820
	ldflags += [ "-Wl,--gdb-index" ]
	}
	} else if (symbol_level == 1) {
	cflags += [ "-g1" ]
	# For linetable-only -g1 builds, --gdb-index makes links ~8% slower, but
	# links are 4x faster than -g builds so it's a fairly small absolute cost.
	# On the other hand, gdb startup is well below 1s with and without the
	# index, and people using -g1 likely don't use a debugger. So don't use
	# the flag here.
	}
	if (is_optimized) {
	cflags += [ "-O3" ]
	}
	cflags += [ "-fdiagnostics-color" ]
	if (use_lld) {
	ldflags += [ "-Wl,--color-diagnostics" ]
	}
	cflags_cc += [
	"-std=c++14",
	"-fvisibility-inlines-hidden",
	]
	} else {
	if (symbol_level != 0) {
	cflags += [
	"/Zi",
	"/FS",
	]
	if (symbol_level == 1 && is_clang) {
	cflags += [ "-gline-tables-only" ]
	}
	ldflags += [ "/DEBUG" ]

	# Speed up links with ghash on windows.
	if (use_lld && is_clang) {
	cflags += [ "-gcodeview-ghash" ]
	ldflags += [ "/DEBUG:GHASH" ]
	}
	}
	if (is_optimized) {
	cflags += [
	"/O2",
	"/Gw",
	"/Zc:inline",
	]
	ldflags += [
	"/OPT:REF",
	"/OPT:ICF",
	]
	}
	defines += [
	"_CRT_SECURE_NO_DEPRECATE",
	"_CRT_SECURE_NO_WARNINGS",
	"_CRT_NONSTDC_NO_DEPRECATE",
	"_CRT_NONSTDC_NO_WARNINGS",
	"_SCL_SECURE_NO_DEPRECATE",
	"_SCL_SECURE_NO_WARNINGS",

	"_HAS_EXCEPTIONS=0",
	"_UNICODE",
	"UNICODE",
	]
	cflags += [ "/EHs-c-" ]

	# The MSVC default value (1 MB) is not enough for parsing recursive C++
	# templates in Clang.
	ldflags += [ "/STACK:10000000" ]
	}

	# Warning setup.
	if (host_os == "win" && !is_clang) {
	cflags += [
	# Suppress ''modifier' : used more than once' (__forceinline and inline).
	"-wd4141",

	# Suppress 'conversion from 'type1' to 'type2', possible loss of data'.
	"-wd4244",

	# Suppress 'conversion from 'size_t' to 'type', possible loss of data'.
	"-wd4267",

	# Suppress 'no matching operator delete found'.
	"-wd4291",

	# Suppress 'noexcept used with no exception handling mode specified'.
	"-wd4577",

	# Suppress 'destructor was implicitly defined as deleted'.
	"-wd4624",

	# Suppress 'unsafe mix of type <type> and type <type> in operation'.
	"-wd4805",
	]
	} else {
	if (host_os == "win") {
	cflags += [ "/W4" ]
	} else {
	cflags += [
	"-Wall",
	"-Wextra",
	]
	}
	cflags += [ "-Wno-unused-parameter" ]
	if (is_clang) {
	cflags += [
	"-Wdelete-non-virtual-dtor",
	"-Wstring-conversion",
	]
	} else {
	cflags += [
	# GCC's -Wcomment complains about // comments ending with '\' if the
	# next line is also a // comment.
	"-Wno-comment",

	# Disable gcc's potentially uninitialized use analysis as it presents
	# lots of false positives.
	"-Wno-maybe-uninitialized",
	]
	cflags_cc += [
	# The LLVM libraries have no stable C++ API, so -Wnoexcept-type is not
	# useful.
	"-Wno-noexcept-type",
	]
	if (gcc_version >= 8) {
	cflags_cc += [
	# Disable -Wclass-memaccess, a C++-only warning from GCC 8 that fires
	# on LLVM's ADT classes.
	"-Wno-class-memaccess",
	]
	}
	if (gcc_version >= 9) {
	cflags_cc += [
	# Disable -Wredundant-move on GCC>=9. GCC wants to remove std::move
	# in code like "A foo(ConvertibleToA a) { return std::move(a); }",
	# but this code does not compile (or uses the copy constructor
	# instead) on clang<=3.8. Clang also has a -Wredundant-move, but it
	# only fires when the types match exactly, so we can keep it here.
	"-Wno-redundant-move",
	]
	}
	}
	if (is_clang && use_goma) {
	# goma converts all paths to lowercase on the server, breaking this
	# warning.
	cflags += [ "-Wno-nonportable-include-path" ]
	}
	}

	# On Windows, the linker is not invoked through the compiler driver.
	if (use_lld && host_os != "win") {
	ldflags += [ "-fuse-ld=lld" ]
	}

	if (llvm_build_instrumented_coverage) {
	cflags += [
	"-fcoverage-mapping",

	# For build determinism. Using this requires passing --compilation-dir to
	# llvm/utils/prepare-code-coverage-artifact.py.
	"-fcoverage-compilation-dir=.",

	# Using an absolute path here is lame, but it's used at test execution
	# time to generate the profiles, and lit doesn't specify a fixed folder
	# for test execution -- so this is the only way to get all profiles into
	# a single folder like llvm/utils/prepare-code-coverage-artifact.py
	# expects.
	"-fprofile-instr-generate=" +
	rebase_path("$root_build_dir/profiles/%4m.profraw"),
	]
	if (host_os != "win") {
	ldflags += [ "-fprofile-instr-generate" ]
	}
	}

	# Deterministic build setup, see
	# http://blog.llvm.org/2019/11/deterministic-builds-with-clang-and-lld.html
	if (current_os == "win") {
	ldflags += [ "/pdbaltpath:%_PDB%" ]
	}
	if (is_clang) {
	cflags += [
	"-no-canonical-prefixes",
	"-Werror=date-time",
	]
	if (current_os == "win") {
	cflags += [ "-fmsc-version=1916" ]
	if (use_lld) {
	cflags += [ "/Brepro" ]
	ldflags += [ "/Brepro" ]
	}
	}
	if (use_relative_paths_in_debug_info) {
	cflags += [ "-fdebug-compilation-dir=." ]
	}
	}
	if (sysroot != "") {
	if (current_os == "win") {
	assert(is_clang, "sysroot only works with clang-cl as host compiler")
	cflags += [ "/winsysroot" + rebase_path(sysroot, root_build_dir) ]
	} else if (current_os != "ios" && current_os != "mac" &&
	current_os != "android") {
	cflags += [ "--sysroot=" + rebase_path(sysroot, root_build_dir) ]
	}
	}
	if ((current_os == "ios" \|\| current_os == "mac") &&
	(clang_base_path != "" \|\| sysroot != "")) {
	if (current_os == "ios" && current_cpu == "arm64") {
	sdk_path = ios_sdk_path
	} else if (current_os == "ios" && current_cpu == "x64") {
	sdk_path = iossim_sdk_path
	} else if (current_os == "mac") {
	sdk_path = mac_sdk_path
	}
	cflags += [
	"-isysroot",
	rebase_path(sdk_path, root_build_dir),
	]
	ldflags += [
	"-isysroot",
	rebase_path(sdk_path, root_build_dir),
	]
	}
	if (sysroot != "" && current_os != "win" && is_clang) {
	cflags += [ "-Wpoison-system-directories" ]
	}
	assert(
	!use_goma \|\| sysroot != "",
	"goma needs a sysroot: run `llvm/utils/sysroot.py make-fake --out-dir=sysroot` and add `sysroot = \"//sysroot\"` to your args.gn")

	if (use_ubsan) {
	assert(is_clang && current_os == "linux",
	"ubsan only supported on Linux/Clang")
	cflags += [
	"-fsanitize=undefined",
	"-fno-sanitize-recover=all",
	]
	ldflags += [ "-fsanitize=undefined" ]
	}

	if (use_asan) {
	assert(is_clang && (current_os == "ios" \|\| current_os == "linux" \|\|
	current_os == "mac"),
	"asan only supported on iOS/Clang, Linux/Clang, and macOS/Clang")
	cflags += [ "-fsanitize=address" ]
	ldflags += [ "-fsanitize=address" ]
	}

	if (use_tsan) {
	assert(is_clang && current_os == "linux",
	"tsan only supported on Linux/Clang")
	cflags += [ "-fsanitize=thread" ]
	ldflags += [ "-fsanitize=thread" ]
	}

	if (use_thinlto) {
	assert(is_clang, "ThinLTO only supported on Clang")

	lto_opt_level = 2

	cflags += [ "-flto=thin" ]

	if (host_os == "win") {
	ldflags += [
	"/opt:lldlto=" + lto_opt_level,
	"/opt:lldltojobs=" + max_jobs_per_lto_link,
	]
	} else {
	ldflags += [
	"-flto=thin",
	"-Wl,--thinlto-jobs=" + max_jobs_per_lto_link,
	"-Wl,--lto-O" + lto_opt_level,
	]
	}
	}

	cflags_objcc = cflags_cc
	}

	config("no_exceptions") {
	cflags_cc = []
	if (host_os != "win") {
	cflags_cc += [ "-fno-exceptions" ]
	}
	cflags_objcc = cflags_cc
	}

	config("no_rtti") {
	if (current_os == "win") {
	cflags_cc = [ "/GR-" ]
	} else {
	cflags_cc = [ "-fno-rtti" ]
	}
	cflags_objcc = cflags_cc
	}

	config("zdefs") {
	# -Wl,-z,defs doesn't work with sanitizers.
	# https://clang.llvm.org/docs/AddressSanitizer.html
	if (current_os != "ios" && current_os != "mac" && current_os != "win" &&
	!(use_asan \|\| use_tsan \|\| use_ubsan)) {
	ldflags = [ "-Wl,-z,defs" ]
	}
	}

	# To make an archive that can be distributed, you need to remove this config and
	# set complete_static_lib.
	config("thin_archive") {
	if (current_os != "ios" && current_os != "mac" && current_os != "win") {
	arflags = [ "-T" ]
	}
	}

	config("llvm_code") {
	include_dirs = [
	"//llvm/include",
	"$root_gen_dir/llvm/include",
	]
	if (current_os != "win") {
	cflags = [ "-fPIC" ]
	}
	}

	config("lld_code") {
	include_dirs = [
	"//lld/include",
	"$root_gen_dir/lld/include",
	]
	}

	config("clang_code") {
	if (host_os != "win") {
	cflags = [ "-fno-strict-aliasing" ]
	}
	include_dirs = [
	"//clang/include",
	"$root_gen_dir/clang/include",
	]
	}

	config("crt_code") {
	include_dirs = [ "//compiler-rt/lib" ]
	cflags = [
	"-fPIC",
	"-funwind-tables",
	"-gline-tables-only",
	"-fvisibility=hidden",
	]
	if (is_clang) {
	cflags += [
	"-Werror=thread-safety",
	"-Werror=thread-safety-reference",
	"-Werror=thread-safety-beta",
	]
	}
	}

	config("lldb_code") {
	if (host_os != "win") {
	cflags = [ "-fno-strict-aliasing" ]
	}
	include_dirs = [
	"//lldb/include",
	"$root_gen_dir/lldb/include",
	]
	}

	config("warn_covered_switch_default") {
	if (is_clang) {
	cflags = [ "-Wcovered-switch-default" ]
	}
	}