avcodec/x86/lossless_videoencdsp: Remove obsolete MMX function

The only systems which benefit from ff_diff_bytes_mmx are truely
ancient 32bit x86s as all other systems use at least the SSE2 versions
(this includes all x64 cpus (which is why this code is restricted
to x86-32)).

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

libavcodec/x86/lossless_videoencdsp.asm

@@ -113,15 +113,6 @@ cglobal diff_bytes, 4,5,2, dst, src1, src2, w
     REP_RET
 %endmacro
 
-%if ARCH_X86_32
-INIT_MMX mmx
-DIFF_BYTES_PROLOGUE
-    %define regsize mmsize
-    DIFF_BYTES_LOOP_PREP .skip_main_aa, .end_aa
-    DIFF_BYTES_BODY    a, a
-%undef i
-%endif
-
 INIT_XMM sse2
 DIFF_BYTES_PROLOGUE
     %define regsize mmsize

libavcodec/x86/lossless_videoencdsp_init.c

@@ -29,8 +29,6 @@
 #include "libavcodec/lossless_videoencdsp.h"
 #include "libavcodec/mathops.h"
 
-void ff_diff_bytes_mmx(uint8_t *dst, const uint8_t *src1, const uint8_t *src2,
-                       intptr_t w);
 void ff_diff_bytes_sse2(uint8_t *dst, const uint8_t *src1, const uint8_t *src2,
                         intptr_t w);
 void ff_diff_bytes_avx2(uint8_t *dst, const uint8_t *src1, const uint8_t *src2,
@@ -87,10 +85,6 @@ av_cold void ff_llvidencdsp_init_x86(LLVidEncDSPContext *c)
 {
     av_unused int cpu_flags = av_get_cpu_flags();
 
-    if (ARCH_X86_32 && EXTERNAL_MMX(cpu_flags)) {
-        c->diff_bytes = ff_diff_bytes_mmx;
-    }
-
 #if HAVE_INLINE_ASM
     if (INLINE_MMXEXT(cpu_flags)) {
         c->sub_median_pred = sub_median_pred_mmxext;