remove extra libtorch dependency

this diff removes extra libtorch dependency on cuda delegate, and introd missing bf16 and int64 shim layers

Differential Revision: [D84207378](https://our.internmc.facebook.com/intern/diff/D84207378/)

[ghstack-poisoned]

Author: Gasoonjia

backends/aoti/CMakeLists.txt

@@ -40,7 +40,7 @@ target_compile_options(aoti_common PUBLIC -fexceptions -frtti -fPIC)
 # Ensure symbols are exported properly
 target_link_options(aoti_common PUBLIC -Wl,--export-dynamic)
 
-# Link against PyTorch libraries and standard libraries
+# Link against ExecuTorch libraries and standard libraries
 target_link_libraries(aoti_common PUBLIC extension_tensor ${CMAKE_DL_LIBS})
 executorch_target_link_options_shared_lib(aoti_common)
 

backends/aoti/common_shims.cpp

@@ -127,11 +127,18 @@ int32_t aoti_torch_layout_strided() {
 }
 
 // Dtype constants - these return the PyTorch dtype codes
-// Currently only float32 is supported, but using robust enum-based approach
 int32_t aoti_torch_dtype_float32() {
   return 6; // PyTorch's float32 dtype code
 }
 
+int32_t aoti_torch_dtype_bfloat16() {
+  return 15; // PyTorch's bfloat16 dtype code
+}
+
+int32_t aoti_torch_dtype_int64() {
+  return 4; // PyTorch's int64 dtype code
+}
+
 // Cleanup functions
 void cleanup_tensor_metadata() {
   internal::tensor_to_sizes.clear();

backends/aoti/common_shims.h

@@ -58,6 +58,8 @@ AOTITorchError aoti_torch_get_dim(Tensor* tensor, int64_t* ret_dim);
 int32_t aoti_torch_device_type_cpu();
 int32_t aoti_torch_layout_strided();
 int32_t aoti_torch_dtype_float32();
+int32_t aoti_torch_dtype_bfloat16();
+int32_t aoti_torch_dtype_int64();
 
 // Autograd mode functions
 int32_t aoti_torch_grad_mode_is_enabled();

backends/cuda/CMakeLists.txt

@@ -55,10 +55,7 @@ target_link_options(aoti_cuda PUBLIC -Wl,--export-dynamic)
 
 # Link against CUDA::cudart, common AOTI library, and PyTorch CUDA libraries
 target_link_libraries(
-  aoti_cuda
-  PUBLIC aoti_common CUDA::cudart ${CMAKE_DL_LIBS}
-         # Link PyTorch libraries for AOTI CUDA functions
-         ${TORCH_LIBRARIES}
+  aoti_cuda PUBLIC aoti_common CUDA::cudart ${CMAKE_DL_LIBS}
 )
 # If you need other CUDA libraries, link them similarly:
 # target_link_libraries(aoti_cuda PUBLIC CUDA::cublas CUDA::cufft ...)