Metal backend: Implement the AOTI MPS shim (#15022)

Includes:
- Shader library management
- Kernel function handling
- Command buffer execution
- Metal memory operations

Author: manuelcandales

backends/apple/metal/runtime/shims/shim_mps.h

@@ -0,0 +1,118 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <executorch/backends/apple/metal/runtime/shims/types.h>
+
+namespace executorch {
+namespace backends {
+namespace metal {
+
+struct AOTIMetalKernelFunctionOpaque;
+using AOTIMetalKernelFunctionHandle = AOTIMetalKernelFunctionOpaque*;
+
+struct AOTIMetalShaderLibraryOpaque;
+using AOTIMetalShaderLibraryHandle = AOTIMetalShaderLibraryOpaque*;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// MetalShaderLibrary functions
+AOTITorchError aoti_torch_mps_create_shader_library(
+    const char* metal_shader_source,
+    AOTIMetalShaderLibraryHandle* library_handle);
+
+AOTITorchError aoti_torch_mps_delete_shader_library(
+    AOTIMetalShaderLibraryHandle library_handle);
+
+AOTITorchError aoti_torch_mps_get_kernel_function(
+    AOTIMetalShaderLibraryHandle library_handle,
+    const char* kernel_name,
+    AOTIMetalKernelFunctionHandle* function_handle);
+
+// MetalKernelFunction functions
+AOTITorchError aoti_torch_mps_start_encoding(
+    AOTIMetalKernelFunctionHandle func);
+
+AOTITorchError aoti_torch_mps_set_arg_tensor(
+    AOTIMetalKernelFunctionHandle func,
+    unsigned idx,
+    AOTITensorHandle tensor);
+
+AOTITorchError aoti_torch_mps_set_arg_int(
+    AOTIMetalKernelFunctionHandle func,
+    unsigned idx,
+    int64_t val);
+
+// Pure C dispatch functions - single value versions
+AOTITorchError aoti_torch_mps_dispatch_single(
+    AOTIMetalKernelFunctionHandle func,
+    uint64_t length);
+
+AOTITorchError aoti_torch_mps_dispatch_single_with_group_size(
+    AOTIMetalKernelFunctionHandle func,
+    uint64_t length,
+    uint64_t group_size);
+
+// Pure C dispatch functions - array versions
+AOTITorchError aoti_torch_mps_dispatch_array(
+    AOTIMetalKernelFunctionHandle func,
+    const uint64_t* length,
+    size_t length_size);
+
+AOTITorchError aoti_torch_mps_dispatch_array_with_group_size(
+    AOTIMetalKernelFunctionHandle func,
+    const uint64_t* length,
+    size_t length_size,
+    const uint64_t* group_size,
+    size_t group_size_size);
+
+// Memory management functions
+AOTITorchError aoti_torch_mps_malloc(void** buffer, size_t num_bytes);
+
+AOTITorchError aoti_torch_mps_free(void* ptr);
+
+AOTITorchError aoti_torch_mps_memcpy(
+    void* buffer,
+    size_t constant_offset,
+    size_t bytes_read,
+    size_t data_size,
+    uint8_t* constants_start);
+
+AOTITorchError aoti_torch_mps_copy_buffer(
+    void* src_buffer,
+    void* dst_buffer,
+    size_t data_size,
+    size_t src_offset,
+    size_t dst_offset);
+
+// C callback function type for command block execution
+typedef void (*aoti_torch_mps_command_block_callback_t)(
+    AOTIMetalKernelFunctionHandle func,
+    void* user_data);
+
+// Shared callback function for std::function trampoline
+void aoti_torch_mps_shared_callback(
+    AOTIMetalKernelFunctionHandle func,
+    void* user_data);
+
+// Pure C version using function pointer and user data for trampoline pattern
+AOTITorchError aoti_torch_mps_run_command_block(
+    AOTIMetalKernelFunctionHandle func,
+    aoti_torch_mps_command_block_callback_t callback,
+    void* user_data);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
+} // namespace metal
+} // namespace backends
+} // namespace executorch