Revert of Revert of SSE4 opaque blend using intrinsics instead of assembly.

src/opts/SkBlitRow_opts_SSE4.cpp

Index: src/opts/SkBlitRow_opts_SSE4.cpp
diff --git a/src/opts/SkBlitRow_opts_SSE4.cpp b/src/opts/SkBlitRow_opts_SSE4.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..fd837d54fee4d879fd3d1d25887c343d1c51279c
--- /dev/null
+++ b/src/opts/SkBlitRow_opts_SSE4.cpp
@@ -0,0 +1,66 @@
+#include "SkBlitRow_opts_SSE4.h"
+
+// Some compilers can't compile SSSE3 or SSE4 intrinsics.  We give them stub methods.
+// The stubs should never be called, so we make them crash just to confirm that.
+#if SK_CPU_SSE_LEVEL < SK_CPU_SSE_LEVEL_SSE41
+void S32A_Opaque_BlitRow32_SSE4(SkPMColor* SK_RESTRICT, const SkPMColor* SK_RESTRICT, int, U8CPU) {
+    sk_throw();
+}
+
+#else
+
+#include <emmintrin.h>  // SSE2:   Most _mm_foo() in this file.
+#include <smmintrin.h>  // SSE4.1: _mm_testz_si128 and _mm_testc_si128.
+
+#include "SkColorPriv.h"
+#include "SkColor_opts_SSE2.h"
+
+void S32A_Opaque_BlitRow32_SSE4(SkPMColor* SK_RESTRICT dst,
+                                const SkPMColor* SK_RESTRICT src,
+                                int count,
+                                U8CPU alpha) {
+    SkASSERT(alpha == 255);
+    // As long as we can, we'll work on 16 pixel pairs at once.
+    int count16 = count / 16;
+    __m128i* dst4 = (__m128i*)dst;
+    const __m128i* src4 = (const __m128i*)src;
+
+    for (int i = 0; i < count16 * 4; i += 4) {
+        // Load 16 source pixels.
+        __m128i s0 = _mm_loadu_si128(src4+i+0),
+                s1 = _mm_loadu_si128(src4+i+1),
+                s2 = _mm_loadu_si128(src4+i+2),
+                s3 = _mm_loadu_si128(src4+i+3);
+
+        const __m128i alphaMask = _mm_set1_epi32(0xFF << SK_A32_SHIFT);
+        const __m128i ORed = _mm_or_si128(s3, _mm_or_si128(s2, _mm_or_si128(s1, s0)));
+        if (_mm_testz_si128(ORed, alphaMask)) {
+            // All 16 source pixels are fully transparent.  There's nothing to do!
+            continue;
+        }
+        const __m128i ANDed = _mm_and_si128(s3, _mm_and_si128(s2, _mm_and_si128(s1, s0)));
+        if (_mm_testc_si128(ANDed, alphaMask)) {
+            // All 16 source pixels are fully opaque.  There's no need to read dst or blend it.
+            _mm_storeu_si128(dst4+i+0, s0);
+            _mm_storeu_si128(dst4+i+1, s1);
+            _mm_storeu_si128(dst4+i+2, s2);
+            _mm_storeu_si128(dst4+i+3, s3);
+            continue;
+        }
+        // The general slow case: do the blend for all 16 pixels.
+        _mm_storeu_si128(dst4+i+0, SkPMSrcOver_SSE2(s0, _mm_loadu_si128(dst4+i+0)));
+        _mm_storeu_si128(dst4+i+1, SkPMSrcOver_SSE2(s1, _mm_loadu_si128(dst4+i+1)));
+        _mm_storeu_si128(dst4+i+2, SkPMSrcOver_SSE2(s2, _mm_loadu_si128(dst4+i+2)));
+        _mm_storeu_si128(dst4+i+3, SkPMSrcOver_SSE2(s3, _mm_loadu_si128(dst4+i+3)));
+    }
+
+    // Wrap up the last <= 15 pixels.
+    for (int i = count16*16; i < count; i++) {
+        // This check is not really necessarily, but it prevents pointless autovectorization.
+        if (src[i] & 0xFF000000) {
+            dst[i] = SkPMSrcOver(src[i], dst[i]);
+        }
+    }
+}
+
+#endif