Fix optional neon support

On Android, we detect neon support at runtime and switch implementations
based on that. This requires that some parts of skia are compiled with
-mfpu=neon.

To support this, the -mfpu flag is moved out of the 'compiler' config
and into its own config. A target can then remove this config and supply
its own -mfpu flag (without having to duplicate all the other stuff in
the 'compiler' config).

BUG=359249

Review URL: https://codereview.chromium.org/371853007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286038 0039d316-1c4b-4281-b951-d872f2087c98

build/config/BUILDCONFIG.gn

@@ -310,6 +310,7 @@ _native_compiler_configs = [
   "//build/config:feature_flags",
 
   "//build/config/compiler:compiler",
+  "//build/config/compiler:compiler_arm_fpu",
   "//build/config/compiler:chromium_code",
   "//build/config/compiler:default_include_dirs",
   "//build/config/compiler:default_warnings",

build/config/arm.gni

@@ -21,7 +21,7 @@ if (cpu_arch == "arm") {
 
   if (is_android) {
     arm_use_neon = false
-    arm_optionally_use_neon = false
+    arm_optionally_use_neon = true
   } else {
     arm_use_neon = true
     arm_optionally_use_neon = true

build/config/compiler/BUILD.gn

@@ -134,7 +134,6 @@ config("compiler") {
       if (!is_android_webview_build) {
         cflags += [
           "-march=$arm_arch",
-          "-mfpu=$arm_fpu",
           "-mfloat-abi=$arm_float_abi",
         ]
         if (arm_tune != "") {
@@ -314,6 +313,14 @@ config("compiler") {
   }
 }
 
+config("compiler_arm_fpu") {
+  if (cpu_arch == "arm" && !is_android_webview_build) {
+    cflags = [
+      "-mfpu=$arm_fpu",
+    ]
+  }
+}
+
 # runtime_library -------------------------------------------------------------
 #
 # Sets the runtime library and associated options.

skia/BUILD.gn

@@ -180,6 +180,15 @@ config("skia_library_config") {
     "SK_USE_DISCARDABLE_SCALEDIMAGECACHE",
   ]
 
+  if (cpu_arch == "arm") {
+    if (arm_use_neon) {
+      defines += [ "__ARM_HAVE_NEON" ]
+    }
+    if (arm_optionally_use_neon) {
+      defines += [ "__ARM_HAVE_OPTIONAL_NEON_SUPPORT" ]
+    }
+  }
+
   # Settings for text blitting, chosen to approximate the system browser.
   if (is_linux) {
     defines += [
@@ -626,20 +635,18 @@ source_set("skia_opts") {
 
         # Root build config sets -mfpu=$arm_fpu, which we expect to be neon
         # when running this.
-        assert(arm_fpu == "neon")
+        if (!arm_use_neon) {
+          configs -= [ "//build/config/compiler:compiler_arm_fpu" ]
+          cflags += [
+            "-mfpu=neon"
+          ]
+        }
 
         #ldflags = [
         #  "-march=armv7-a",
         #  "-Wl,--fix-cortex-a8",
         #]
       }
-
-      if (arm_use_neon) {
-        defines += [ "__ARM_HAVE_NEON" ]
-      }
-      if (arm_optionally_use_neon) {
-        defines += [ "__ARM_HAVE_OPTIONAL_NEON_SUPPORT" ]
-      }
     }
 
     # Non-Neon ARM code.