CUDA: add fast walsh-hadamard transform (#23615)

* CUDA: add fast walsh-hadamard transform

* review: add unrolls + change size_t -> int

* warp size 64

---------

Co-authored-by: Johannes Gäßler <johannesg@5d6.de>

ggml/src/ggml-cuda/ggml-cuda.cu

@@ -24,6 +24,7 @@
 #include "ggml-cuda/diagmask.cuh"
 #include "ggml-cuda/diag.cuh"
 #include "ggml-cuda/fattn.cuh"
+#include "ggml-cuda/fwht.cuh"
 #include "ggml-cuda/getrows.cuh"
 #include "ggml-cuda/im2col.cuh"
 #include "ggml-cuda/mmf.cuh"
@@ -2594,6 +2595,13 @@ static void ggml_cuda_mul_mat(ggml_backend_cuda_context & ctx, const ggml_tensor
     bool use_batched_cublas_bf16 = src0->type == GGML_TYPE_BF16 && bf16_mma_hardware_available(cc);
     bool use_batched_cublas_f32  = src0->type == GGML_TYPE_F32;
 
+    const int32_t hint = ggml_get_op_params_i32(dst, 1);
+    if (hint == GGML_HINT_SRC0_IS_HADAMARD) {
+        GGML_ASSERT(!split);
+        ggml_cuda_op_fwht(ctx, src1, dst);
+        return;
+    }
+
     if (!split && use_mul_mat_vec_f) {
         // the custom F16 vector kernel can be used over batched cuBLAS GEMM
         // but this is only faster for GPUs without tensor cores or with a thin src0 matrix (particularly KQV in attention)