Fix for png encoding performance regressions (part 2)

third_party/libpng/BUILD.gn

 # Copyright 2014 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/chromecast_build.gni")
 import("//build/config/arm.gni")
 
 config("libpng_config") {
   include_dirs = [ "." ]
 
@@ skipping 15 matching lines @@
   if (is_clang) {
     cflags = [
       # libpng checks that the width is not greater than PNG_SIZE_MAX.
       # On platforms where size_t is 64-bits, this comparison will always
       # be false.
       "-Wno-tautological-constant-out-of-range-compare",
     ]
   }
 }
 
+# Must be in a config because of how GN orders flags (otherwise the default
+# flags will appear after this and turn these back off).  This is a fix for
+# png encoding performance regressions (crbug.com/619850).
+config("android_gcc_optimizations") {
+  if (is_android && !is_clang) {
+    cflags = [
+      "-O2",
+      "-finline-functions",
+    ]
+  }
+}
+
+# Must be in a config because of how GN orders flags (otherwise the default
+# flags will appear after this and turn these back off).  This is a fix for
+# png encoding performance regressions (crbug.com/619850).
+config("msvs_optimizations") {
+  if (is_win && !is_clang) {

[Nico, 2016/07/01 14:12:33]

why `!is_clang`?

[msarett, 2016/07/01 14:44:33]

Possibly this is unnecessary...  I'll remove if you think it's best.

Clang builds on Mac/Linux were fixed without changing any compiler flags, so I'm
assuming that there is no need for this flag on Windows clang.  But I'm actually
not sure.  And I think that the perf bots are MSVC (not that I can get them to
work anyway), so I don't know how to test Win clang.

But this feels right because I'd expect that if/when Windows is switched to
clang, we'll catch regressions.

+    cflags = [
+      "/O2",
+    ]
+  }
+}
+
 source_set("libpng_sources") {
   sources = [
     "png.c",
     "png.h",
     "pngconf.h",
     "pngerror.c",
     "pngget.c",
     "pnginfo.h",
     "pnglibconf.h",
     "pngmem.c",
@@ skipping 45 matching lines @@
     defines += [ "PNG_BUILD_DLL" ]
   }
 
   public_configs = [ ":libpng_config" ]
 
   public_deps = [
     "//third_party/zlib",
   ]
 
   configs += [ ":clang_warnings" ]
+  configs += [ ":android_gcc_optimizations" ]
+  configs += [ ":msvs_optimizations" ]
 }
 
 if (is_win) {
   component("libpng") {
     public_deps = [
       ":libpng_sources",
     ]
   }
 } else {
   group("libpng") {
     public_deps = [
       ":libpng_sources",
     ]
   }
 }