avcodec: [loongarch] Optimize prefetch with loongarch.

./ffmpeg -i ../1_h264_1080p_30fps_3Mbps.mp4 -f rawvideo -y /dev/null -an
before:296
after :308

Reviewed-by: 殷时友 <yinshiyou-hf@loongson.cn>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/loongarch/Makefile

@@ -7,6 +7,7 @@ OBJS-$(CONFIG_VP9_DECODER)            += loongarch/vp9dsp_init_loongarch.o
 OBJS-$(CONFIG_VC1DSP)                 += loongarch/vc1dsp_init_loongarch.o
 OBJS-$(CONFIG_HPELDSP)                += loongarch/hpeldsp_init_loongarch.o
 OBJS-$(CONFIG_IDCTDSP)                += loongarch/idctdsp_init_loongarch.o
+OBJS-$(CONFIG_VIDEODSP)               += loongarch/videodsp_init.o
 LASX-OBJS-$(CONFIG_H264CHROMA)        += loongarch/h264chroma_lasx.o
 LASX-OBJS-$(CONFIG_H264QPEL)          += loongarch/h264qpel_lasx.o
 LASX-OBJS-$(CONFIG_H264DSP)           += loongarch/h264dsp_lasx.o \

libavcodec/loongarch/videodsp_init.c

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2021 Loongson Technology Corporation Limited
+ * Contributed by Xiwei Gu <guxiwei-hf@loongson.cn>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "libavcodec/videodsp.h"
+#include "libavutil/attributes.h"
+
+static void prefetch_loongarch(uint8_t *mem, ptrdiff_t stride, int h)
+{
+    register const uint8_t *p = mem;
+
+    __asm__ volatile (
+        "1:                                     \n\t"
+        "preld      0,     %[p],     0          \n\t"
+        "preld      0,     %[p],     32         \n\t"
+        "addi.d     %[h],  %[h],     -1         \n\t"
+        "add.d      %[p],  %[p],     %[stride]  \n\t"
+
+        "blt        $r0,   %[h],     1b         \n\t"
+        : [p] "+r" (p), [h] "+r" (h)
+        : [stride] "r" (stride)
+    );
+}
+
+av_cold void ff_videodsp_init_loongarch(VideoDSPContext *ctx, int bpc)
+{
+    ctx->prefetch = prefetch_loongarch;
+}

libavcodec/videodsp.c

@@ -54,4 +54,6 @@ av_cold void ff_videodsp_init(VideoDSPContext *ctx, int bpc)
         ff_videodsp_init_x86(ctx, bpc);
     if (ARCH_MIPS)
         ff_videodsp_init_mips(ctx, bpc);
+    if (ARCH_LOONGARCH64)
+        ff_videodsp_init_loongarch(ctx, bpc);
 }

libavcodec/videodsp.h

@@ -84,5 +84,6 @@ void ff_videodsp_init_arm(VideoDSPContext *ctx, int bpc);
 void ff_videodsp_init_ppc(VideoDSPContext *ctx, int bpc);
 void ff_videodsp_init_x86(VideoDSPContext *ctx, int bpc);
 void ff_videodsp_init_mips(VideoDSPContext *ctx, int bpc);
+void ff_videodsp_init_loongarch(VideoDSPContext *ctx, int bpc);
 
 #endif /* AVCODEC_VIDEODSP_H */