Revert of Revert of Sync Windows build flags between GYP and GN

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")
 if (current_cpu == "arm") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
@@ skipping 1073 matching lines @@
 # Note that BUILDCONFIG.gn sets up a variable "default_optimization_config"
 # which it will assign to the config it implicitly applies to every target. If
 # you want to override the optimization level for your target, remove this
 # config (which will expand differently for debug or release builds), and then
 # add back the one you want to override it with:
 #
 #   configs -= default_optimization_config
 #   configs += [ "//build/config/compiler/optimize_max" ]
 
 # Shared settings for both "optimize" and "optimize_max" configs.
+# IMPORTANT: On Windows "/O1" and "/O2" must go before the common flags.
 if (is_win) {
   common_optimize_on_cflags = [
-    "/O2",
-    "/Ob2",  # both explicit and auto inlining.
-    "/Oy-",  # disable omitting frame pointers, must be after /o2.
-    "/Os",  # favor size over speed.
+    "/Ob2",  # Both explicit and auto inlining.
+    "/Oy-",  # Disable omitting frame pointers, must be after /O2.
   ]
   if (!is_asan) {
     common_optimize_on_cflags += [
       # Put data in separate COMDATs. This allows the linker
       # to put bit-identical constants at the same address even if
       # they're unrelated constants, which saves binary size.
       # This optimization can't be used when ASan is enabled because
       # it is not compatible with the ASan ODR checker.
       "/Gw",
     ]
@@ skipping 45 matching lines @@
       # Functions interposed by the sanitizers can make ld think
       # that some libraries aren't needed when they actually are,
       # http://crbug.com/234010. As workaround, disable --as-needed.
       common_optimize_on_ldflags += [ "-Wl,--as-needed" ]
     }
   }
 }
 
 # Default "optimization on" config. On Windows, this favors size over speed.
 config("optimize") {
-  cflags = common_optimize_on_cflags
+  if (is_win) {
+    # Favor size over speed, /O1 must be before the common flags. The GYP
+    # build also specifies /Os and /GF but these are implied by /O1.
+    cflags = [ "/O1" ] + common_optimize_on_cflags + [ "/Oi" ]
+  } else if (is_android || is_ios) {
+    cflags = [ "-Os" ] + common_optimize_on_cflags  # Favor size over speed.
+  } else {
+    cflags = [ "-O2" ] + common_optimize_on_cflags
+  }
   ldflags = common_optimize_on_ldflags
-  if (is_win) {
-    cflags += [ "/Os" ]  # favor size over speed.
-  } else if (is_android || is_ios) {
-    cflags += [ "-Os" ]  # Favor size over speed.
-  } else {
-    cflags += [ "-O2" ]
-  }
 }
 
 # Turn off optimizations.
 config("no_optimize") {
   if (is_win) {
     cflags = [
       "/Od",  # Disable optimization.
       "/Ob0",  # Disable all inlining (on by default).
       "/RTC1",  # Runtime checks for stack frame and uninitialized variables.
     ]
@@ skipping 11 matching lines @@
     ldflags = common_optimize_on_ldflags
   } else {
     cflags = [ "-O0" ]
   }
 }
 
 # Turns up the optimization level. On Windows, this implies whole program
 # optimization and link-time code generation which is very expensive and should
 # be used sparingly.
 config("optimize_max") {
-  cflags = common_optimize_on_cflags
   ldflags = common_optimize_on_ldflags
   if (is_win) {
-    cflags -= [ "/Os" ]
-    cflags += [ "/Ot" ]  # Favor speed over size.
+    # Favor speed over size, /O2 must be before the common flags. The GYP
+    # build also specifies /Ot, /Oi, and /GF, but these are implied by /O2.
+    cflags = [ "/O2" ] + common_optimize_on_cflags
     if (is_official_build) {
       # TODO(GYP): TODO(dpranke): Should these only be on in an official
       # build, or on all the time? For now we'll require official build so
       # that the compile is clean.
       cflags += [
         "/GL",  # Whole program optimization.
 
         # Disable Warning 4702 ("Unreachable code") for the WPO/PGO builds.
         # Probably anything that this would catch that wouldn't be caught in a
         # normal build isn't going to actually be a bug, so the incremental
         # value of C4702 for PGO builds is likely very small.
         "/wd4702",
       ]
       ldflags += [ "/LTCG" ]
     }
   } else {
-    cflags += [ "-O2" ]
+    cflags = [ "-O2" ] + common_optimize_on_cflags
   }
 }
 
 # Symbols ----------------------------------------------------------------------
 
 config("symbols") {
   if (is_win) {
     import("//build/toolchain/goma.gni")
     if (use_goma) {
       cflags = [ "/Z7" ]  # No PDB file
@@ skipping 19 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }