Move cuda.core Windows stub-lib generation into build_ext. (#2033)

Reuse setuptools' initialized MSVC compiler when linking _tensor_bridge so Windows source builds do not need separate toolchain discovery in build_hooks.py.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: rwgk

cuda_core/build_hooks.py

@@ -11,7 +11,6 @@
 import glob
 import os
 import re
-import subprocess
 import sys
 import tempfile
 import zipfile
@@ -185,28 +184,6 @@ def get_sources(mod_name):
         # related to free-threading builds.
         extra_compile_args += ["-DCYTHON_TRACE_NOGIL=1", "-DCYTHON_USE_SYS_MONITORING=0"]
 
-    # On Windows, _tensor_bridge.pyx needs a stub import library so the MSVC
-    # linker can resolve the AOTI symbols (they live in torch_cpu.dll at
-    # runtime).  We generate the .lib from a .def file at build time.
-    # Note: aoti_torch_get_current_cuda_stream lives in torch_cuda.dll and
-    # is resolved lazily at runtime (not via the stub lib) — see
-    # _tensor_bridge.pyx.
-    _aoti_extra_link_args = []
-    if sys.platform == "win32":
-        _def_file = os.path.join("cuda", "core", "_include", "aoti_shim.def")
-        _lib_file = os.path.join("build", "aoti_shim.lib")
-        os.makedirs("build", exist_ok=True)
-        subprocess.check_call(  # noqa: S603
-            ["lib", f"/DEF:{_def_file}", f"/OUT:{_lib_file}", "/MACHINE:X64"],  # noqa: S607
-            stdout=subprocess.DEVNULL,
-        )
-        _aoti_extra_link_args = [_lib_file]
-
-    def get_extra_link_args(mod_name):
-        if mod_name == "_tensor_bridge" and _aoti_extra_link_args:
-            return extra_link_args + _aoti_extra_link_args
-        return extra_link_args
-
     ext_modules = tuple(
         Extension(
             f"cuda.core.{mod.replace(os.path.sep, '.')}",
@@ -218,7 +195,7 @@ def get_extra_link_args(mod_name):
             + all_include_dirs,
             language="c++",
             extra_compile_args=extra_compile_args,
-            extra_link_args=get_extra_link_args(mod),
+            extra_link_args=extra_link_args,
         )
         for mod in module_names()
     )

cuda_core/cuda/core/_include/aoti_shim.def

@@ -4,7 +4,7 @@
 ; At runtime the symbols resolve from torch_cpu.dll (loaded by 'import torch').
 ;
 ; IMPORTANT: Keep this export list in sync with the AOTI_SHIM_API declarations
-; in aoti_shim.h. build_hooks.py turns this file into the stub import library
+; in aoti_shim.h. setup.py turns this file into the stub import library
 ; that MSVC uses to link _tensor_bridge, so any added/removed/renamed AOTI
 ; symbol must be updated in both files.
 LIBRARY torch_cpu.dll

cuda_core/cuda/core/_include/aoti_shim.h

@@ -52,10 +52,10 @@ typedef struct AtenTensorOpaque* AtenTensorHandle;
 
 /*
  * IMPORTANT: Keep the AOTI_SHIM_API declaration list below in sync with
- * aoti_shim.def.  On Windows, build_hooks.py turns that .def file into the
- * stub import library that MSVC needs to link _tensor_bridge without making
- * PyTorch a build-time dependency.  If you add, remove, or rename an
- * imported AOTI symbol here, update aoti_shim.def in the same change.
+ * aoti_shim.def.  On Windows, setup.py generates that stub import library
+ * during build_ext so MSVC can link _tensor_bridge without making PyTorch a
+ * build-time dependency.  If you add, remove, or rename an imported AOTI
+ * symbol here, update aoti_shim.def in the same change.
  *
  * Exception: aoti_torch_get_current_cuda_stream lives in torch_cuda (not
  * torch_cpu) and is resolved lazily at runtime — see _tensor_bridge.pyx.

cuda_core/setup.py

@@ -3,6 +3,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
 import os
+from pathlib import Path
 
 import build_hooks  # our build backend
 from setuptools import setup
@@ -11,11 +12,63 @@
 
 nthreads = int(os.environ.get("CUDA_PYTHON_PARALLEL_LEVEL", os.cpu_count() // 2))
 coverage_mode = bool(int(os.environ.get("CUDA_PYTHON_COVERAGE", "0")))
+_ROOT_DIR = Path(__file__).resolve().parent
+_AOTI_SHIM_DEF_FILE = _ROOT_DIR / "cuda" / "core" / "_include" / "aoti_shim.def"
+_AOTI_SHIM_LIB_FILE = _ROOT_DIR / "build" / "aoti_shim.lib"
+_TENSOR_BRIDGE_EXT_NAME = "cuda.core._tensor_bridge"
+
+
+def _ensure_compiler_initialized(compiler, plat_name):
+    initialize = getattr(compiler, "initialize", None)
+    if callable(initialize) and not getattr(compiler, "initialized", False):
+        if plat_name is None:
+            initialize()
+        else:
+            initialize(plat_name)
+
+
+def _build_aoti_shim_lib(compiler):
+    # Reuse setuptools' initialized MSVC compiler instead of rediscovering
+    # lib.exe separately in the build backend.
+    lib_exe = getattr(compiler, "lib", None)
+    if not lib_exe:
+        raise RuntimeError("MSVC compiler did not expose lib.exe after initialization.")
+
+    _AOTI_SHIM_LIB_FILE.parent.mkdir(exist_ok=True)
+    compiler.spawn(
+        [
+            lib_exe,
+            f"/DEF:{_AOTI_SHIM_DEF_FILE}",
+            f"/OUT:{_AOTI_SHIM_LIB_FILE}",
+            "/MACHINE:X64",
+        ]
+    )
+    return str(_AOTI_SHIM_LIB_FILE)
 
 
 class build_ext(_build_ext):  # noqa: N801
+    def _configure_windows_tensor_bridge(self):
+        if os.name != "nt" or getattr(self.compiler, "compiler_type", None) != "msvc":
+            return
+
+        # _tensor_bridge imports AOTI symbols from torch_cpu.dll, which on
+        # Windows requires a stub import library for the MSVC linker.
+        for ext in self.extensions:
+            if ext.name != _TENSOR_BRIDGE_EXT_NAME:
+                continue
+
+            _ensure_compiler_initialized(self.compiler, self.plat_name)
+            shim_lib = _build_aoti_shim_lib(self.compiler)
+            link_args = list(ext.extra_link_args or [])
+            if shim_lib not in link_args:
+                ext.extra_link_args = [*link_args, shim_lib]
+            return
+
+        raise RuntimeError(f"Failed to find extension {_TENSOR_BRIDGE_EXT_NAME!r} for Windows build.")
+
     def build_extensions(self):
         self.parallel = nthreads
+        self._configure_windows_tensor_bridge()
         super().build_extensions()