ARGBExtractAlpha 16 pixels at a time for ARM

source/row_neon.cc

Index: source/row_neon.cc
diff --git a/source/row_neon.cc b/source/row_neon.cc
index 7574cee85e252159238fd6bac14c73ab7604a13f..9e60237ec4aa63c830a41fe154e3c157c43822f1 100644
--- a/source/row_neon.cc
+++ b/source/row_neon.cc
@@ -1302,16 +1302,17 @@ void ARGBExtractAlphaRow_NEON(const uint8* src_argb, uint8* dst_a, int width) {
   asm volatile (
   "1:                                          \n"
     MEMACCESS(0)
-    "vld4.8     {d0, d1, d2, d3}, [%0]!        \n"  // load row 8 pixels
-    "subs       %2, %2, #8                     \n"  // 8 processed per loop
+    "vld4.8     {d0, d2, d4, d6}, [%0]!        \n"  // load 8 ARGB pixels
+    "vld4.8     {d1, d3, d5, d7}, [%0]!        \n"  // load next 8 ARGB pixels
+    "subs       %2, %2, #16                    \n"  // 16 processed per loop
     MEMACCESS(1)
-    "vst1.8     {d3}, [%1]!                    \n"  // store 8 A's.
+    "vst1.8     {q3}, [%1]!                    \n"  // store 16 A's.
     "bgt       1b                              \n"
   : "+r"(src_argb),   // %0
     "+r"(dst_a),      // %1
     "+r"(width)       // %2
   :
-  : "cc", "memory", "d0", "d1", "d2", "d3"  // Clobber List
+  : "cc", "memory", "q0", "q1", "q2", "q3"  // Clobber List
   );
 }