libgav1,BUILD.gn: split sse4 files to a separate target

this allows flagging the code with -msse4.1; fixes a build failure with
clang-cl as for msvc builds sse4 support is assumed, but clang-cl
requires the -m flag to enable it.

Bug: 1151489
Change-Id: I3d29e5c3d4985b76ad44e9ca15886c0428c5c140
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2561030
Commit-Queue: James Zern <jzern@google.com>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832690}

third_party/libgav1/BUILD.gn

@@ -59,10 +59,31 @@ if (enable_libgav1_decoder || use_libgav1_parser) {
     configs += [ "//build/config/compiler:no_chromium_code" ]
     configs += [ ":private_libgav1_config" ]
 
+    deps = [
+      ":libgav1_dsp_sse4",
+      ":libgav1_utils",
+    ]
+    public_configs = [ ":public_libgav1_config" ]
+
+    sources = gav1_dsp_sources + gav1_dsp_headers_sources
+  }
+
+  # SSE4 sources are split to their own target as Chrome is currently built
+  # with -msse3.
+  source_set("libgav1_dsp_sse4") {
+    configs -= [ "//build/config/compiler:chromium_code" ]
+    configs += [ "//build/config/compiler:no_chromium_code" ]
+    configs += [ ":private_libgav1_config" ]
+
     deps = [ ":libgav1_utils" ]
     public_configs = [ ":public_libgav1_config" ]
 
-    sources = gav1_dsp_sources
+    if (current_cpu == "x86" || current_cpu == "x64") {
+      cflags = [ "-msse4.1" ]
+    }
+
+    sources = gav1_dsp_sse4_sources + gav1_dsp_sse4_headers_sources +
+              gav1_dsp_headers_sources
   }
 
   static_library("libgav1") {

third_party/libgav1/generate_libgav1_src_gni.go

@@ -101,8 +101,28 @@ func main() {
 		found := false
 		for _, d := range topDirs {
 			if strings.HasPrefix(f, d) {
-				bd := filepath.Base(d)
-				m[bd] = append(m[bd], f)
+				var bd string
+				for _, asm := range []string{"sse4"} {
+					pattern := "*_" + asm + "*"
+					if match, err := filepath.Match(pattern, filepath.Base(f)); err != nil {
+						panic(err)
+					} else if match {
+						bd = filepath.Base(d) + "_" + asm
+						break
+					}
+				}
+				if bd == "" {
+					bd = filepath.Base(d)
+				}
+
+				// Split the dsp headers out to their own variables as the
+				// assembly may depend on both its headers and the top-level
+				// headers.
+				if strings.HasPrefix(bd, "dsp") && filepath.Ext(f) == ".h" {
+					m[bd+"_headers"] = append(m[bd+"_headers"], f)
+				} else {
+					m[bd] = append(m[bd], f)
+				}
 				found = true
 				break
 			}