Remove 2nd-order transform for first-order DC coefficients.

Since addition of the larger-scale transforms (16x16, 32x32), these
don't give a benefit at macroblock-sizes anymore. At superblock-sizes,
2nd-order transform was never used over the larger transforms. Future
work should test whether there is a benefit for that use case.

Change-Id: I90cadfc42befaf201de3eb0c4f7330c56e33330a

3 files changed, 77 insertions, 14 deletions

diff --git a/vp9/decoder/vp9_decodframe.c b/vp9/decoder/vp9_decodframe.c
index 3324186ef..9f4db6bf7 100644
--- a/vp9/decoder/vp9_decodframe.c
+++ b/vp9/decoder/vp9_decodframe.c
@@ -304,7 +304,8 @@ static void decode_8x8(VP9D_COMP *pbi, MACROBLOCKD *xd,
                                    0, xd->eobs[idx]);
       }
     }
-  } else if (xd->mode_info_context->mbmi.mode == SPLITMV) {
+  } else if (xd->mode_info_context->mbmi.mode == SPLITMV ||
+             get_2nd_order_usage(xd) == 0) {
     assert(get_2nd_order_usage(xd) == 0);
     vp9_dequant_idct_add_y_block_8x8(xd->qcoeff,
                                      xd->block[0].dequant,
@@ -450,7 +451,7 @@ static void decode_4x4(VP9D_COMP *pbi, MACROBLOCKD *xd,
                            xd->dst.v_buffer,
                            xd->dst.uv_stride,
                            xd->eobs + 16);
-  } else if (mode == SPLITMV) {
+  } else if (mode == SPLITMV || get_2nd_order_usage(xd) == 0) {
     assert(get_2nd_order_usage(xd) == 0);
     pbi->idct_add_y_block(xd->qcoeff,
                           xd->block[0].dequant,
@@ -595,13 +596,8 @@ static void decode_8x8_sb(VP9D_COMP *pbi, MACROBLOCKD *xd,
             + x_idx * 16 + (i & 1) * 8,
             stride, stride, 0, b->eob);
       }
-      vp9_dequant_idct_add_uv_block_8x8_inplace_c(
-          xd->qcoeff + 16 * 16, xd->block[16].dequant,
-          xd->dst.u_buffer + y_idx * 8 * xd->dst.uv_stride + x_idx * 8,
-          xd->dst.v_buffer + y_idx * 8 * xd->dst.uv_stride + x_idx * 8,
-          xd->dst.uv_stride, xd->eobs + 16, xd);
     }
-  } else {
+  } else if (get_2nd_order_usage(xd) == 1) {
     vp9_dequantize_b_2x2(b);
     vp9_short_ihaar2x2(&b->dqcoeff[0], b->diff, 8);
     ((int *)b->qcoeff)[0] = 0;  // 2nd order block are set to 0 after idct
@@ -616,12 +612,17 @@ static void decode_8x8_sb(VP9D_COMP *pbi, MACROBLOCKD *xd,
         xd->qcoeff, xd->block[0].dequant,
         xd->dst.y_buffer + y_idx * 16 * xd->dst.y_stride + x_idx * 16,
         xd->dst.y_stride, xd->eobs, xd->block[24].diff, xd);
-    vp9_dequant_idct_add_uv_block_8x8_inplace_c(
-        xd->qcoeff + 16 * 16, xd->block[16].dequant,
-        xd->dst.u_buffer + y_idx * 8 * xd->dst.uv_stride + x_idx * 8,
-        xd->dst.v_buffer + y_idx * 8 * xd->dst.uv_stride + x_idx * 8,
-        xd->dst.uv_stride, xd->eobs + 16, xd);
+  } else {
+    vp9_dequant_idct_add_y_block_8x8_inplace_c(
+        xd->qcoeff, xd->block[0].dequant,
+        xd->dst.y_buffer + y_idx * 16 * xd->dst.y_stride + x_idx * 16,
+        xd->dst.y_stride, xd->eobs, xd);
   }
+  vp9_dequant_idct_add_uv_block_8x8_inplace_c(
+      xd->qcoeff + 16 * 16, xd->block[16].dequant,
+      xd->dst.u_buffer + y_idx * 8 * xd->dst.uv_stride + x_idx * 8,
+      xd->dst.v_buffer + y_idx * 8 * xd->dst.uv_stride + x_idx * 8,
+      xd->dst.uv_stride, xd->eobs + 16, xd);
 };
 
 static void decode_4x4_sb(VP9D_COMP *pbi, MACROBLOCKD *xd,
@@ -653,7 +654,7 @@ static void decode_4x4_sb(VP9D_COMP *pbi, MACROBLOCKD *xd,
             xd->dst.y_stride, xd->dst.y_stride);
       }
     }
-  } else {
+  } else if (get_2nd_order_usage(xd) == 1) {
     vp9_dequantize_b(b);
     if (xd->eobs[24] > 1) {
       vp9_short_inv_walsh4x4(&b->dqcoeff[0], b->diff);
@@ -673,6 +674,11 @@ static void decode_4x4_sb(VP9D_COMP *pbi, MACROBLOCKD *xd,
         xd->qcoeff, xd->block[0].dequant,
         xd->dst.y_buffer + y_idx * 16 * xd->dst.y_stride + x_idx * 16,
         xd->dst.y_stride, xd->eobs, xd->block[24].diff, xd);
+  } else {
+    vp9_dequant_idct_add_y_block_4x4_inplace_c(
+        xd->qcoeff, xd->block[0].dequant,
+        xd->dst.y_buffer + y_idx * 16 * xd->dst.y_stride + x_idx * 16,
+        xd->dst.y_stride, xd->eobs, xd);
   }
   vp9_dequant_idct_add_uv_block_4x4_inplace_c(
       xd->qcoeff + 16 * 16, xd->block[16].dequant,
diff --git a/vp9/decoder/vp9_dequantize.h b/vp9/decoder/vp9_dequantize.h
index 2a0ae80e8..2edbd6a3a 100644
--- a/vp9/decoder/vp9_dequantize.h
+++ b/vp9/decoder/vp9_dequantize.h
@@ -77,6 +77,12 @@ void vp9_dequant_dc_idct_add_y_block_8x8_inplace_c(int16_t *q, const int16_t *dq
                                                    const int16_t *dc,
                                                    MACROBLOCKD *xd);
 
+void vp9_dequant_idct_add_y_block_8x8_inplace_c(int16_t *q, const int16_t *dq,
+                                                unsigned char *dst,
+                                                int stride,
+                                                uint16_t *eobs,
+                                                MACROBLOCKD *xd);
+
 void vp9_dequant_dc_idct_add_y_block_4x4_inplace_c(int16_t *q, const int16_t *dq,
                                                    unsigned char *dst,
                                                    int stride,
@@ -84,6 +90,12 @@ void vp9_dequant_dc_idct_add_y_block_4x4_inplace_c(int16_t *q, const int16_t *dq
                                                    const int16_t *dc,
                                                    MACROBLOCKD *xd);
 
+void vp9_dequant_idct_add_y_block_4x4_inplace_c(int16_t *q, const int16_t *dq,
+                                                unsigned char *dst,
+                                                int stride,
+                                                uint16_t *eobs,
+                                                MACROBLOCKD *xd);
+
 void vp9_dequant_idct_add_uv_block_8x8_inplace_c(int16_t *q, const int16_t *dq,
                                                  unsigned char *dstu,
                                                  unsigned char *dstv,
diff --git a/vp9/decoder/vp9_idct_blk.c b/vp9/decoder/vp9_idct_blk.c
index 152527cff..b350e4d68 100644
--- a/vp9/decoder/vp9_idct_blk.c
+++ b/vp9/decoder/vp9_idct_blk.c
@@ -64,6 +64,31 @@ void vp9_dequant_dc_idct_add_y_block_4x4_inplace_c(int16_t *q,
   }
 }
 
+void vp9_dequant_idct_add_y_block_4x4_inplace_c(int16_t *q,
+                                                const int16_t *dq,
+                                                uint8_t *dst,
+                                                int stride,
+                                                uint16_t *eobs,
+                                                MACROBLOCKD *xd) {
+  int i, j;
+
+  for (i = 0; i < 4; i++) {
+    for (j = 0; j < 4; j++) {
+      if (*eobs++ > 1) {
+        vp9_dequant_idct_add_c(q, dq, dst, dst, stride, stride);
+      } else {
+        vp9_dc_only_idct_add_c(q[0]*dq[0], dst, dst, stride, stride);
+        ((int *)q)[0] = 0;
+      }
+
+      q   += 16;
+      dst += 4;
+    }
+
+    dst += 4 * stride - 16;
+  }
+}
+
 void vp9_dequant_idct_add_y_block_c(int16_t *q, const int16_t *dq,
                                     uint8_t *pre,
                                     uint8_t *dst,
@@ -221,6 +246,26 @@ void vp9_dequant_dc_idct_add_y_block_8x8_inplace_c(int16_t *q,
                                 xd->eobs[12]);
 }
 
+void vp9_dequant_idct_add_y_block_8x8_inplace_c(int16_t *q,
+                                                const int16_t *dq,
+                                                uint8_t *dst,
+                                                int stride,
+                                                uint16_t *eobs,
+                                                MACROBLOCKD *xd) {
+  vp9_dequant_idct_add_8x8_c(q, dq, dst, dst, stride, stride, 0, xd->eobs[0]);
+
+  vp9_dequant_idct_add_8x8_c(&q[64], dq, dst + 8,
+                             dst + 8, stride, stride, 0, xd->eobs[4]);
+
+  vp9_dequant_idct_add_8x8_c(&q[128], dq, dst + 8 * stride,
+                             dst + 8 * stride, stride, stride, 0,
+                             xd->eobs[8]);
+
+  vp9_dequant_idct_add_8x8_c(&q[192], dq, dst + 8 * stride + 8,
+                             dst + 8 * stride + 8, stride, stride, 0,
+                             xd->eobs[12]);
+}
+
 void vp9_dequant_idct_add_y_block_8x8_c(int16_t *q, const int16_t *dq,
                                         uint8_t *pre,
                                         uint8_t *dst,