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.
+    "/GF",  # Enable string pooling.

[scottmg, 2015/06/16 20:07:48]

looks like this is on by default for O1 and O2 too too so could probably drop
here, but also fine if you want to kepe it for consistency (I might keep /Os in
that case then too)

[brettw, 2015/06/16 21:02:28]

I'll remove it.

   ]
   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 but this is 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 /O2 and /Oi but these are implied by /O2.
+    cflags = [ "/O2" ] + common_optimize_on_cflags
     if (is_official_build && !is_clang) {
       # 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.
       # TODO(hans): Remove Clang special-case when it rolls past r239656.
       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" ]
   }
 }