metal : add f16 and bf16 support for concat operator (#24724)

* metal : add f16 and bf16 support for concat operator

Extend the Metal backend concat operator to support f16 and bf16 tensor
types in addition to the existing f32 and i32 support.

- Template kernel_concat on type T with specializations for float, half,
  bfloat, and int
- Add type-specific pipeline getter ggml_metal_library_get_pipeline_concat()
- Update device support check to allow f16 unconditionally and bf16 when
  device supports bfloat16
- Update dispatch to select the correct kernel specialization by type

Assisted-by: pi:llama.cpp/Qwen3.6-27B

* metal : extend concat operator to support f16, bf16, i8, i16 and i64

Assisted-by: pi:llama.cpp/Qwen3.6-27B

ggml/src/ggml-metal/ggml-metal-device.cpp

@@ -66,7 +66,6 @@ struct ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_base(ggml
     const char * op_str = "undefined";
     switch (op) {
         case GGML_OP_ADD_ID: op_str = "add_id"; break;
-        case GGML_OP_CONCAT: op_str = "concat"; break;
         default: GGML_ABORT("fatal error");
     };
 
@@ -211,6 +210,21 @@ ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_repeat(ggml_meta
     return res;
 }
 
+ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_concat(ggml_metal_library_t lib, ggml_type tsrc) {
+    char base[256];
+    char name[256];
+
+    snprintf(base, 256, "kernel_concat_%s", ggml_type_name(tsrc));
+    snprintf(name, 256, "%s", base);
+
+    ggml_metal_pipeline_with_params res = ggml_metal_library_get_pipeline(lib, name);
+    if (!res.pipeline) {
+        res = ggml_metal_library_compile_pipeline(lib, base, name, nullptr);
+    }
+
+    return res;
+}
+
 ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_unary(ggml_metal_library_t lib, const ggml_tensor * op) {
     char base[256];
     char name[256];

ggml/src/ggml-metal/ggml-metal-device.h

@@ -115,6 +115,7 @@ struct ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_get_rows
 struct ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_set_rows          (ggml_metal_library_t lib, enum ggml_type tidx, enum ggml_type tdst);
 struct ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_diag              (ggml_metal_library_t lib, const struct ggml_tensor * op);
 struct ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_repeat            (ggml_metal_library_t lib, enum ggml_type tsrc);
+struct ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_concat            (ggml_metal_library_t lib, enum ggml_type tsrc);
 struct ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_unary             (ggml_metal_library_t lib, const struct ggml_tensor * op);
 struct ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_glu               (ggml_metal_library_t lib, const struct ggml_tensor * op);
 struct ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_sum               (ggml_metal_library_t lib, const struct ggml_tensor * op);

ggml/src/ggml-metal/ggml-metal-device.m

@@ -1123,13 +1123,24 @@ bool ggml_metal_device_supports_op(ggml_metal_device_t dev, const struct ggml_te
             return true;
         case GGML_OP_CONCAT:
             {
-                // kernel_concat copies one float-sized value per element.
-                // Other scalar types need a type-generic copy kernel first.
                 const enum ggml_type src0_type = op->src[0]->type;
                 const enum ggml_type src1_type = op->src[1]->type;
-                return src0_type == src1_type &&
+                if (src0_type != src1_type || src0_type != op->type) {
-                       src0_type == op->type &&
+                    return false;
-                       (src0_type == GGML_TYPE_F32 || src0_type == GGML_TYPE_I32);
+                }
+                switch (src0_type) {
+                    case GGML_TYPE_F32:
+                    case GGML_TYPE_F16:
+                    case GGML_TYPE_I8:
+                    case GGML_TYPE_I16:
+                    case GGML_TYPE_I32:
+                    case GGML_TYPE_I64:
+                        return true;
+                    case GGML_TYPE_BF16:
+                        return has_bfloat;
+                    default:
+                        return false;
+                }
             }
         case GGML_OP_ADD:
         case GGML_OP_SUB:

ggml/src/ggml-metal/ggml-metal-ops.cpp

@@ -556,7 +556,7 @@ int ggml_metal_op_concat(ggml_metal_op_t ctx, int idx) {
         /*.dim  =*/ dim,
     };
 
-    auto pipeline = ggml_metal_library_get_pipeline_base(lib, GGML_OP_CONCAT);
+    auto pipeline = ggml_metal_library_get_pipeline_concat(lib, op->type);
 
     ggml_metal_encoder_set_pipeline(enc, pipeline);
     ggml_metal_encoder_set_bytes   (enc, &args, sizeof(args), 0);

ggml/src/ggml-metal/ggml-metal.metal

@@ -7513,6 +7513,7 @@ template [[host_name("kernel_cpy_q5_0_f16")]] kernel cpy_q_f_t kernel_cpy_q_f32<
 template [[host_name("kernel_cpy_q5_1_f16")]] kernel cpy_q_f_t kernel_cpy_q_f32<half4x4, block_q5_1, 2, dequantize_q5_1>;
 template [[host_name("kernel_cpy_q8_0_f16")]] kernel cpy_q_f_t kernel_cpy_q_f32<half4x4, block_q8_0, 2, dequantize_q8_0>;
 
+template<typename T>
 kernel void kernel_concat(
         constant ggml_metal_kargs_concat & args,
         device  const char * src0,
@@ -7533,21 +7534,31 @@ kernel void kernel_concat(
     int o[4] = {0, 0, 0, 0};
     o[args.dim] = args.dim == 0 ? args.ne00 : (args.dim == 1 ? args.ne01 : (args.dim == 2 ? args.ne02 : args.ne03));
 
-    device const float * x;
-
     for (int i0 = tpitg.x; i0 < args.ne0; i0 += ntg.x) {
+        device const T * x;
+
         if (i0 < args.ne00 && i1 < args.ne01 && i2 < args.ne02 && i3 < args.ne03) {
-            x = (device const float *)(src0 + (i3       )*args.nb03 + (i2       )*args.nb02 + (i1       )*args.nb01 + (i0       )*args.nb00);
+            x = (device const T *)(src0 + (i3       )*args.nb03 + (i2       )*args.nb02 + (i1       )*args.nb01 + (i0       )*args.nb00);
         } else {
-            x = (device const float *)(src1 + (i3 - o[3])*args.nb13 + (i2 - o[2])*args.nb12 + (i1 - o[1])*args.nb11 + (i0 - o[0])*args.nb10);
+            x = (device const T *)(src1 + (i3 - o[3])*args.nb13 + (i2 - o[2])*args.nb12 + (i1 - o[1])*args.nb11 + (i0 - o[0])*args.nb10);
         }
 
-        device float * y = (device float *)(dst + i3*args.nb3 + i2*args.nb2 + i1*args.nb1 + i0*args.nb0);
+        device T * y = (device T *)(dst + i3*args.nb3 + i2*args.nb2 + i1*args.nb1 + i0*args.nb0);
 
         *y = *x;
     }
 }
 
+typedef decltype(kernel_concat<float>) kernel_concat_t;
+
+template [[host_name("kernel_concat_f32")]]  kernel kernel_concat_t kernel_concat<float>;
+template [[host_name("kernel_concat_f16")]]  kernel kernel_concat_t kernel_concat<half>;
+template [[host_name("kernel_concat_bf16")]] kernel kernel_concat_t kernel_concat<bfloat>;
+template [[host_name("kernel_concat_i8")]]   kernel kernel_concat_t kernel_concat<char>;
+template [[host_name("kernel_concat_i16")]]  kernel kernel_concat_t kernel_concat<short>;
+template [[host_name("kernel_concat_i32")]]  kernel kernel_concat_t kernel_concat<int>;
+template [[host_name("kernel_concat_i64")]]  kernel kernel_concat_t kernel_concat<long>;
+
 template<int nr0, typename args_t>
 void kernel_mul_mv_q2_K_f32_impl(
         args_t args,