avcodec/mpv_reconstruct_mb_template: Don't unnecessarily copy data

There is no reason to use a temporary buffer as destination
for the new macroblock before copying it into its proper place.
(Originally, this has been added in commit
b68ab2609c due to concerns about
copying from GPU memory.)

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/mpegpicture.h

@@ -35,7 +35,6 @@ typedef struct ScratchpadContext {
     uint8_t *obmc_scratchpad;
     union {
         uint8_t *scratchpad_buf;  ///< the other *_scratchpad point into this buffer
-        uint8_t *b_scratchpad;    ///< scratchpad used for writing into write only buffers
         uint8_t *rd_scratchpad;   ///< scratchpad for rate distortion mb decision
     };
     int      linesize;            ///< linesize that the buffers in this context have been allocated for

libavcodec/mpv_reconstruct_mb_template.c

@@ -80,11 +80,10 @@ void mpv_reconstruct_mb_internal(MpegEncContext *s, int16_t block[12][64],
           s->avctx->mb_decision != FF_MB_DECISION_RD))  // FIXME precalc
 #endif /* IS_ENCODER */
     {
-        uint8_t *dest_y, *dest_cb, *dest_cr;
+        uint8_t *dest_y = s->dest[0], *dest_cb = s->dest[1], *dest_cr = s->dest[2];
         int dct_linesize, dct_offset;
         const int linesize   = s->cur_pic.linesize[0]; //not s->linesize as this would be wrong for field pics
         const int uvlinesize = s->cur_pic.linesize[1];
-        const int readable   = IS_ENCODER || lowres_flag || s->pict_type != AV_PICTURE_TYPE_B;
         const int block_size = lowres_flag ? 8 >> s->avctx->lowres : 8;
 
         /* avoid copy if macroblock skipped in last frame too */
@@ -106,16 +105,6 @@ void mpv_reconstruct_mb_internal(MpegEncContext *s, int16_t block[12][64],
         dct_linesize = linesize << s->interlaced_dct;
         dct_offset   = s->interlaced_dct ? linesize : linesize * block_size;
 
-        if (readable) {
-            dest_y  = s->dest[0];
-            dest_cb = s->dest[1];
-            dest_cr = s->dest[2];
-        } else {
-            dest_y  = s->sc.b_scratchpad;
-            dest_cb = s->sc.b_scratchpad + 16 * linesize;
-            dest_cr = s->sc.b_scratchpad + 32 * linesize;
-        }
-
         if (!s->mb_intra) {
             /* motion handling */
             /* decoding or more than one mb_type (MC was already done otherwise) */
@@ -169,7 +158,7 @@ void mpv_reconstruct_mb_internal(MpegEncContext *s, int16_t block[12][64],
                 if(  (s->avctx->skip_idct >= AVDISCARD_NONREF && s->pict_type == AV_PICTURE_TYPE_B)
                    ||(s->avctx->skip_idct >= AVDISCARD_NONKEY && s->pict_type != AV_PICTURE_TYPE_I)
                    || s->avctx->skip_idct >= AVDISCARD_ALL)
-                    goto skip_idct;
+                    return;
             }
 
             /* add dct residue */
@@ -288,14 +277,6 @@ void mpv_reconstruct_mb_internal(MpegEncContext *s, int16_t block[12][64],
                     }
                 } //gray
             }
-        }
-skip_idct:
-        if (!readable) {
-            s->hdsp.put_pixels_tab[0][0](s->dest[0], dest_y, linesize, 16);
-            if (!CONFIG_GRAY || !(s->avctx->flags & AV_CODEC_FLAG_GRAY)) {
-                s->hdsp.put_pixels_tab[s->chroma_x_shift][0](s->dest[1], dest_cb, uvlinesize, 16 >> s->chroma_y_shift);
-                s->hdsp.put_pixels_tab[s->chroma_x_shift][0](s->dest[2], dest_cr, uvlinesize, 16 >> s->chroma_y_shift);
-            }
 #endif /* !IS_ENCODER */
         }
     }