Optimize the intra frame decode to skip some unnecessary copy.

This speeds up a normal YT style 1080P clip decode by ~1% on nexus 7.

Change-Id: Ied7fa0d8bc941b2adb4db9382f549ee4d5654f3a

vp9/common/vp9_reconintra.c

@@ -30,6 +30,25 @@ const TX_TYPE intra_mode_to_tx_type_lookup[INTRA_MODES] = {
   ADST_ADST,  // TM
 };
 
+enum {
+  NEED_LEFT = 1 << 1,
+  NEED_ABOVE = 1 << 2,
+  NEED_ABOVERIGHT = 1 << 3,
+};
+
+static const uint8_t extend_modes[INTRA_MODES] = {
+  NEED_ABOVE | NEED_LEFT,       // DC
+  NEED_ABOVE,                   // V
+  NEED_LEFT,                    // H
+  NEED_ABOVERIGHT,              // D45
+  NEED_LEFT | NEED_ABOVE,       // D135
+  NEED_LEFT | NEED_ABOVE,       // D117
+  NEED_LEFT | NEED_ABOVE,       // D153
+  NEED_LEFT,                    // D207
+  NEED_ABOVERIGHT,              // D63
+  NEED_LEFT | NEED_ABOVE,       // TM
+};
+
 // This serves as a wrapper function, so that all the prediction functions
 // can be unified and accessed as a pointer array. Note that the boundary
 // above and left are not necessarily used all the time.
@@ -790,75 +809,106 @@ static void build_intra_predictors(const MACROBLOCKD *xd, const uint8_t *ref,
   x0 = (-xd->mb_to_left_edge >> (3 + pd->subsampling_x)) + x;
   y0 = (-xd->mb_to_top_edge >> (3 + pd->subsampling_y)) + y;
 
-  vpx_memset(left_col, 129, 64);
-
-  // left
-  if (left_available) {
-    if (xd->mb_to_bottom_edge < 0) {
-      /* slower path if the block needs border extension */
-      if (y0 + bs <= frame_height) {
-        for (i = 0; i < bs; ++i)
-          left_col[i] = ref[i * ref_stride - 1];
+  // NEED_LEFT
+  if (extend_modes[mode] & NEED_LEFT) {
+    if (left_available) {
+      if (xd->mb_to_bottom_edge < 0) {
+        /* slower path if the block needs border extension */
+        if (y0 + bs <= frame_height) {
+          for (i = 0; i < bs; ++i)
+            left_col[i] = ref[i * ref_stride - 1];
+        } else {
+          const int extend_bottom = frame_height - y0;
+          for (i = 0; i < extend_bottom; ++i)
+            left_col[i] = ref[i * ref_stride - 1];
+          for (; i < bs; ++i)
+            left_col[i] = ref[(extend_bottom - 1) * ref_stride - 1];
+        }
       } else {
-        const int extend_bottom = frame_height - y0;
-        for (i = 0; i < extend_bottom; ++i)
+        /* faster path if the block does not need extension */
+        for (i = 0; i < bs; ++i)
           left_col[i] = ref[i * ref_stride - 1];
-        for (; i < bs; ++i)
-          left_col[i] = ref[(extend_bottom - 1) * ref_stride - 1];
       }
     } else {
-      /* faster path if the block does not need extension */
-      for (i = 0; i < bs; ++i)
-        left_col[i] = ref[i * ref_stride - 1];
+      vpx_memset(left_col, 129, bs);
     }
   }
 
-  // TODO(hkuang) do not extend 2*bs pixels for all modes.
-  // above
-  if (up_available) {
-    const uint8_t *above_ref = ref - ref_stride;
-    if (xd->mb_to_right_edge < 0) {
-      /* slower path if the block needs border extension */
-      if (x0 + 2 * bs <= frame_width) {
-        if (right_available && bs == 4) {
-          vpx_memcpy(above_row, above_ref, 2 * bs);
+  // NEED_ABOVE
+  if (extend_modes[mode] & NEED_ABOVE) {
+    if (up_available) {
+      const uint8_t *above_ref = ref - ref_stride;
+      if (xd->mb_to_right_edge < 0) {
+        /* slower path if the block needs border extension */
+        if (x0 + bs <= frame_width) {
+          vpx_memcpy(above_row, above_ref, bs);
+        } else if (x0 <= frame_width) {
+          const int r = frame_width - x0;
+          vpx_memcpy(above_row, above_ref, r);
+          vpx_memset(above_row + r, above_row[r - 1],
+                     x0 + bs - frame_width);
+        }
+      } else {
+        /* faster path if the block does not need extension */
+        if (bs == 4 && right_available && left_available) {
+          const_above_row = above_ref;
         } else {
           vpx_memcpy(above_row, above_ref, bs);
-          vpx_memset(above_row + bs, above_row[bs - 1], bs);
         }
-      } else if (x0 + bs <= frame_width) {
-        const int r = frame_width - x0;
-        if (right_available && bs == 4) {
+      }
+      above_row[-1] = left_available ? above_ref[-1] : 129;
+    } else {
+      vpx_memset(above_row, 127, bs);
+      above_row[-1] = 127;
+    }
+  }
+
+  // NEED_ABOVERIGHT
+  if (extend_modes[mode] & NEED_ABOVERIGHT) {
+    if (up_available) {
+      const uint8_t *above_ref = ref - ref_stride;
+      if (xd->mb_to_right_edge < 0) {
+        /* slower path if the block needs border extension */
+        if (x0 + 2 * bs <= frame_width) {
+          if (right_available && bs == 4) {
+            vpx_memcpy(above_row, above_ref, 2 * bs);
+          } else {
+            vpx_memcpy(above_row, above_ref, bs);
+            vpx_memset(above_row + bs, above_row[bs - 1], bs);
+          }
+        } else if (x0 + bs <= frame_width) {
+          const int r = frame_width - x0;
+          if (right_available && bs == 4) {
+            vpx_memcpy(above_row, above_ref, r);
+            vpx_memset(above_row + r, above_row[r - 1],
+                       x0 + 2 * bs - frame_width);
+          } else {
+            vpx_memcpy(above_row, above_ref, bs);
+            vpx_memset(above_row + bs, above_row[bs - 1], bs);
+          }
+        } else if (x0 <= frame_width) {
+          const int r = frame_width - x0;
           vpx_memcpy(above_row, above_ref, r);
           vpx_memset(above_row + r, above_row[r - 1],
                      x0 + 2 * bs - frame_width);
+        }
+      } else {
+        /* faster path if the block does not need extension */
+        if (bs == 4 && right_available && left_available) {
+          const_above_row = above_ref;
         } else {
           vpx_memcpy(above_row, above_ref, bs);
-          vpx_memset(above_row + bs, above_row[bs - 1], bs);
+          if (bs == 4 && right_available)
+            vpx_memcpy(above_row + bs, above_ref + bs, bs);
+          else
+            vpx_memset(above_row + bs, above_row[bs - 1], bs);
         }
-      } else if (x0 <= frame_width) {
-        const int r = frame_width - x0;
-        vpx_memcpy(above_row, above_ref, r);
-        vpx_memset(above_row + r, above_row[r - 1],
-                     x0 + 2 * bs - frame_width);
       }
       above_row[-1] = left_available ? above_ref[-1] : 129;
     } else {
-      /* faster path if the block does not need extension */
-      if (bs == 4 && right_available && left_available) {
-        const_above_row = above_ref;
-      } else {
-        vpx_memcpy(above_row, above_ref, bs);
-        if (bs == 4 && right_available)
-          vpx_memcpy(above_row + bs, above_ref + bs, bs);
-        else
-          vpx_memset(above_row + bs, above_row[bs - 1], bs);
-        above_row[-1] = left_available ? above_ref[-1] : 129;
-      }
+      vpx_memset(above_row, 127, bs * 2);
+      above_row[-1] = 127;
     }
-  } else {
-    vpx_memset(above_row, 127, bs * 2);
-    above_row[-1] = 127;
   }
 
   // predict