add structure for normal SKX opts

My experience porting the old opts over to the current SKX opts setup
was so bad that I don't want to try any more, and think it's probably
safer to port the SKX code to the old setup.

Need to hook up dependents (Chromium and Google3 I think) before we can
move the actual SXK opts code over.

Change-Id: Ibb8bc4a083cb104cd39f27cbfbc16e9eedd9bd46
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/294495
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>

BUILD.gn

@@ -218,6 +218,19 @@ opts("hsw") {
   }
 }
 
+opts("skx") {
+  enabled = is_x86
+  sources = skia_opts.skx_sources
+  if (is_win) {
+    cflags = [ "/arch:AVX512" ]
+  } else {
+    cflags = [ "-march=skylake-avx512" ]
+    if (is_mac && is_debug) {
+      cflags += [ "-fno-stack-check" ]  # Work around skia:9709
+    }
+  }
+}
+
 # Any feature of Skia that requires third-party code should be optional and use this template.
 template("optional") {
   visibility = [ ":*" ]

gn/gn_to_bp.py

@@ -494,7 +494,8 @@ with open('Android.bp', 'w') as Android_bp:
                                              defs['sse41'] +
                                              defs['sse42'] +
                                              defs['avx'  ] +
-                                             defs['hsw'  ])),
+                                             defs['hsw'  ] +
+                                             defs['skx'  ])),
 
     'dm_includes'       : bpfmt(8, dm_includes),
     'dm_srcs'           : bpfmt(8, dm_srcs),

gn/opts.gni

@@ -18,3 +18,4 @@ sse41 = [ "$_src/opts/SkOpts_sse41.cpp" ]
 sse42 = [ "$_src/opts/SkOpts_sse42.cpp" ]
 avx = [ "$_src/opts/SkOpts_avx.cpp" ]
 hsw = [ "$_src/opts/SkOpts_hsw.cpp" ]
+skx = [ "$_src/opts/SkOpts_skx.cpp" ]

gn/shared_sources.gni

@@ -26,4 +26,5 @@ skia_opts = {
   sse42_sources = sse42
   avx_sources = avx
   hsw_sources = hsw
+  skx_sources = skx
 }

src/opts/SkOpts_skx.cpp

@@ -0,0 +1,8 @@
+/*
+ * Copyright 2020 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+// Intentionally empty, to be filled in.