Fix for png encoding performance regressions (part 2)

third_party/libpng/BUILD.gn

Index: third_party/libpng/BUILD.gn
diff --git a/third_party/libpng/BUILD.gn b/third_party/libpng/BUILD.gn
index 7e4bd5e4048067059b18027feebda638e3d4a771..16df1a12ebea803f6d5bb89ab65bf63f64c9fb26 100644
--- a/third_party/libpng/BUILD.gn
+++ b/third_party/libpng/BUILD.gn
@@ -33,6 +33,29 @@ config("clang_warnings") {
   }
 }
 
+# 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",
@@ -98,6 +121,8 @@ source_set("libpng_sources") {
   ]
 
   configs += [ ":clang_warnings" ]
+  configs += [ ":android_gcc_optimizations" ]
+  configs += [ ":msvs_optimizations" ]
 }
 
 if (is_win) {