x86/opusdsp: implement FMA3 accelerated postfilter and deemphasis

58893 decicycles in deemphasis_c,  130548 runs,    524 skips
9475 decicycles in deemphasis_fma3,  130686 runs,    386 skips -> 6.21x speedup

24866 decicycles in postfilter_c,   65386 runs,    150 skips
5268 decicycles in postfilter_fma3,   65505 runs,     31 skips -> 4.72x speedup

Total decoder speedup: ~14%

Deemphasis SIMD based on the following unrolling:
const float c1 = CELT_EMPH_COEFF, c2 = c1*c1, c3 = c2*c1, c4 = c3*c1;
float state = coeff;

for (int i = 0; i < len; i += 4) {
    y[0] = x[0] + c1*state;
    y[1] = x[1] + c2*state + c1*x[0];
    y[2] = x[2] + c3*state + c1*x[1] + c2*x[0];
    y[3] = x[3] + c4*state + c1*x[2] + c2*x[1] + c3*x[0];

    state = y[3];
    y += 4;
    x += 4;
}

1 files changed, 3 insertions, 0 deletions

diff --git a/libavcodec/opusdsp.c b/libavcodec/opusdsp.c
index 615e7d6816..17e819f977 100644
--- a/libavcodec/opusdsp.c
+++ b/libavcodec/opusdsp.c
@@ -58,4 +58,7 @@ av_cold void ff_opus_dsp_init(OpusDSP *ctx)
 {
     ctx->postfilter = postfilter_c;
     ctx->deemphasis = deemphasis_c;
+
+    if (ARCH_X86)
+        ff_opus_dsp_init_x86(ctx);
 }