Add gn option 'is_lto' to enable Link Time Optimization builds.

We'll launch LTO builds on Linux first, and then add CFI
(control flow integrity) on top of that.

BUG=589915

Review URL: https://codereview.chromium.org/1734043003

Cr-Commit-Position: refs/heads/master@{#377695}

4 files changed, 31 insertions, 21 deletions

diff --git a/build/config/sanitizers/BUILD.gn b/build/config/sanitizers/BUILD.gn
index 19af2ba..0b596ba 100644
--- a/build/config/sanitizers/BUILD.gn
+++ b/build/config/sanitizers/BUILD.gn
@@ -92,13 +92,8 @@ config("default_sanitizer_ldflags") {
     if (is_ubsan_vptr) {
       ldflags += [ "-fsanitize=vptr" ]
     }
-    if (is_cfi && !is_nacl) {
-      ldflags += [
-        "-flto",
-        "-fsanitize=cfi-vcall",
-        "-fsanitize=cfi-derived-cast",
-        "-fsanitize=cfi-unrelated-cast",
-      ]
+    if (is_lto && !is_nacl) {
+      ldflags += [ "-flto" ]
 
       # Apply a lower LTO optimization level as the default is too slow.
       if (is_linux) {
@@ -119,6 +114,14 @@ config("default_sanitizer_ldflags") {
         ldflags += [ "-Wl,-plugin-opt,-function-sections" ]
       }
 
+      if (is_cfi) {
+        ldflags += [
+          "-fsanitize=cfi-vcall",
+          "-fsanitize=cfi-derived-cast",
+          "-fsanitize=cfi-unrelated-cast",
+        ]
+      }
+
       if (use_cfi_diag) {
         ldflags += [
           "-fno-sanitize-trap=cfi",
@@ -147,7 +150,7 @@ config("default_sanitizer_flags") {
   if (is_posix) {
     # Common options for AddressSanitizer, LeakSanitizer, ThreadSanitizer,
     # MemorySanitizer and non-official CFI builds.
-    if (using_sanitizer || (is_cfi && !is_official_build)) {
+    if (using_sanitizer || (is_lto && !is_official_build)) {
       cflags += [
         "-fno-omit-frame-pointer",
         "-gline-tables-only",
@@ -243,16 +246,19 @@ config("default_sanitizer_flags") {
         "-fsanitize-blacklist=$ubsan_vptr_blacklist_path",
       ]
     }
-    if (is_cfi && !is_nacl) {
-      cfi_blacklist_path =
-          rebase_path("//tools/cfi/blacklist.txt", root_build_dir)
-      cflags += [
-        "-flto",
-        "-fsanitize=cfi-vcall",
-        "-fsanitize=cfi-derived-cast",
-        "-fsanitize=cfi-unrelated-cast",
-        "-fsanitize-blacklist=$cfi_blacklist_path",
-      ]
+    if (is_lto && !is_nacl) {
+      cflags += [ "-flto" ]
+
+      if (is_cfi) {
+        cfi_blacklist_path =
+            rebase_path("//tools/cfi/blacklist.txt", root_build_dir)
+        cflags += [
+          "-fsanitize=cfi-vcall",
+          "-fsanitize=cfi-derived-cast",
+          "-fsanitize=cfi-unrelated-cast",
+          "-fsanitize-blacklist=$cfi_blacklist_path",
+        ]
+      }
 
       if (use_cfi_diag) {
         cflags += [
diff --git a/build/config/sanitizers/sanitizers.gni b/build/config/sanitizers/sanitizers.gni
index bd89cdb..0323807 100644
--- a/build/config/sanitizers/sanitizers.gni
+++ b/build/config/sanitizers/sanitizers.gni
@@ -68,6 +68,10 @@ declare_args() {
   use_custom_libcxx =
       (is_asan && is_linux) || is_tsan || is_msan || is_ubsan || use_libfuzzer
 
+  # Enable Link Time Optimization (output programs runs faster,
+  # but linking is up to 5-20x slower.
+  is_lto = is_cfi
+
   use_sanitizer_coverage = use_libfuzzer
 }
 
diff --git a/build/toolchain/gcc_toolchain.gni b/build/toolchain/gcc_toolchain.gni
index 0c314bb..a6b3add 100644
--- a/build/toolchain/gcc_toolchain.gni
+++ b/build/toolchain/gcc_toolchain.gni
@@ -9,7 +9,7 @@ import("//build/toolchain/goma.gni")
 import("//build/toolchain/toolchain.gni")
 
 # This value will be inherited in the toolchain below.
-if (is_cfi) {
+if (is_lto) {
   concurrent_links =
       exec_script("get_concurrent_links.py", [ "--lto" ], "value")
 } else {
@@ -217,7 +217,7 @@ template("gcc_toolchain") {
     tool("alink") {
       rspfile = "{{output}}.rsp"
       arflags = ""
-      if (is_cfi && invoker.toolchain_os != "nacl") {
+      if (is_lto && invoker.toolchain_os != "nacl") {
         gold_plugin_path = rebase_path(
                 "//third_party/llvm-build/Release+Asserts/lib/LLVMgold.so",
                 root_build_dir)
diff --git a/build/toolchain/win/BUILD.gn b/build/toolchain/win/BUILD.gn
index 1934e9b..7c359b8 100644
--- a/build/toolchain/win/BUILD.gn
+++ b/build/toolchain/win/BUILD.gn
@@ -25,7 +25,7 @@ if (use_goma) {
 }
 
 # This value will be inherited in the toolchain below.
-if (is_cfi) {
+if (is_lto) {
   concurrent_links =
       exec_script("../get_concurrent_links.py", [ "--lto" ], "value")
 } else {