simplify torch.utils.cpp_extension.include_paths; use it in cpp_build…

…er (pytorch#145480)

While working on conda-forge integration, I needed to look at the way the include paths are calculated, and noticed an avoidable duplication between `torch/utils/cpp_extension.py` and `torch/_inductor/cpp_builder.py`. The latter already imports the former anyway, so simply reuse the same function.

Furthermore, remove long-obsolete include-paths. AFAICT, the `/TH` headers have not existed since pytorch 1.11.

Pull Request resolved: pytorch#145480
Approved by: https://github.com/ezyang

torch/_inductor/cpp_builder.py

@@ -762,16 +762,9 @@ def _get_build_args_of_chosen_isa(vec_isa: VecISA) -> tuple[list[str], list[str]
 def _get_torch_related_args(
     include_pytorch: bool, aot_mode: bool
 ) -> tuple[list[str], list[str], list[str]]:
-    from torch.utils.cpp_extension import _TORCH_PATH, TORCH_LIB_PATH
-
-    include_dirs = [
-        os.path.join(_TORCH_PATH, "include"),
-        os.path.join(_TORCH_PATH, "include", "torch", "csrc", "api", "include"),
-        # Some internal (old) Torch headers don't properly prefix their includes,
-        # so we need to pass -Itorch/lib/include/TH as well.
-        os.path.join(_TORCH_PATH, "include", "TH"),
-        os.path.join(_TORCH_PATH, "include", "THC"),
-    ]
+    from torch.utils.cpp_extension import include_paths, TORCH_LIB_PATH
+
+    include_dirs = include_paths()
     libraries_dirs = [TORCH_LIB_PATH]
     libraries = []
     if sys.platform != "darwin" and not config.is_fbcode():

torch/utils/cpp_extension.py

@@ -1220,10 +1220,6 @@ def include_paths(device_type: str = "cpu") -> list[str]:
         lib_include,
         # Remove this once torch/torch.h is officially no longer supported for C++ extensions.
         os.path.join(lib_include, 'torch', 'csrc', 'api', 'include'),
-        # Some internal (old) Torch headers don't properly prefix their includes,
-        # so we need to pass -Itorch/lib/include/TH as well.
-        os.path.join(lib_include, 'TH'),
-        os.path.join(lib_include, 'THC')
     ]
     if device_type == "cuda" and IS_HIP_EXTENSION:
         paths.append(os.path.join(lib_include, 'THH'))