On Zen4 repack fp16 models to bf16_r16 when run-time-repacking is requested (#174)

This massively improves performance. As this is opt-in, we do not worry
about possible precision loss in the f16 -> bf16 conversion.

Co-authored-by: Iwan Kawrakow <[email protected]>

Author: ikawrakow

ggml/src/iqk/iqk_quantize.cpp

@@ -5260,6 +5260,7 @@ inline ggml_bf16_t to_bf16(const float& x) {
     helper.f = x;
     return ggml_bf16_t{(uint16_t)(helper.u >> 16)};
 }
+inline ggml_bf16_t to_bf16(const ggml_half& x) { return to_bf16(GGML_FP16_TO_FP32(x)); }
 inline ggml_bf16_t to_bf16(const ggml_bf16_t& x) { return x; }
 template <typename T>
 void repack_bf16(int nrows, int n_per_row, const T * x, ggml_bf16_t * y) {
@@ -6082,7 +6083,8 @@ void iqk_repack_tensor(struct ggml_tensor * tensor) {
         { GGML_TYPE_Q8_0,   { GGML_TYPE_Q8_0_R4,   4,  (Repack::repack_func)repack_q8_0}    },
         { GGML_TYPE_Q8_K,   { GGML_TYPE_Q8_K_R8,   8,  (Repack::repack_func)repack_q8_k}    },
 #ifdef __AVX512BF16__
-        { GGML_TYPE_BF16,   { GGML_TYPE_BF16_R16, 16,  (Repack::repack_func)repack_bf16<ggml_bf16_t>}    },
+        { GGML_TYPE_BF16,   { GGML_TYPE_BF16_R16, 16,  (Repack::repack_func)repack_bf16<ggml_bf16_t>}},
+        { GGML_TYPE_F16,    { GGML_TYPE_BF16_R16, 16,  (Repack::repack_func)repack_bf16<ggml_half>}  },
 #endif
     };