Add an optimize_for_fuzzing GN flag to build with -O1

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 68 matching lines @@
   # Enable fatal linker warnings. Building Chromium with certain versions
   # of binutils can cause linker warning.
   # See: https://bugs.chromium.org/p/chromium/issues/detail?id=457359
   fatal_linker_warnings = true
 
   # AFDO (Automatic Feedback Directed Optimizer) is a form of profile-guided
   # optimization that GCC supports. It used by ChromeOS in their official
   # builds. To use it, set auto_profile_path to the path to a file containing
   # the needed gcov profiling data.
   auto_profile_path = ""
+
+  # Optimize for coverage guided fuzzing (balance between speed and number of
+  # branches)
+  optimize_for_fuzzing = false
 }
 
 if (is_clang && !is_nacl) {
   update_args = [ "--print-revision" ]
   if (llvm_force_head_revision) {
     update_args += [ "--llvm-force-head-revision" ]
   }
   clang_revision =
       exec_script("//tools/clang/scripts/update.py", update_args, "trim string")
 }
@@ skipping 1355 matching lines @@
           # value of C4702 for PGO builds is likely very small.
           "/wd4702",
         ]
       }
     } else {
       cflags = [ "-O3" ] + common_optimize_on_cflags
     }
   }
 }
 
+config("optimize_fuzzing") {
+  cflags = [ "-O1" ] + common_optimize_on_cflags
+  ldflags = common_optimize_on_ldflags
+  visibility = [ ":default_optimization" ]
+}
+
 # The default optimization applied to all targets. This will be equivalent to
 # either "optimize" or "no_optimize", depending on the build flags.
 config("default_optimization") {
   if (is_nacl_irt) {
     # The NaCl IRT is a special case and always wants its own config.
     # It gets optimized the same way regardless of the type of build.
     configs = [ "//build/config/nacl:irt_optimize" ]
   } else if (is_debug) {
     configs = [ ":no_optimize" ]
+  } else if (optimize_for_fuzzing) {
+    assert(!is_win, "Fuzzing optimize level not supported on Windows")
+    configs = [ ":optimize_fuzzing" ]
   } else {
     configs = [ ":optimize" ]
   }
 }
 
 # GCC supports a form of profile-guided optimization called AFDO, which
 # is used by ChromeOS in their official builds. However,
 # //base/allocator:tcmalloc currently doesn't work correctly with AFDO
 # so we provide separate config so that the flag can be disabled per-target.
 # TODO(crbug.com/633719): Remove this config once tcmalloc works with AFDO
@@ skipping 115 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }