Remove redundant MSVC_Z7_OVERRIDE processing and combine "/EHa" flag …

…setup (#23455)

Summary:
- MSVC_Z7_OVERRIDE has already handled in CMakeLists.txt. No need to process it for once more in the Python scripts.
- Option MSVC_Z7_OVERRIDE should be visible to the user only if MSVC is used.
- Move the setting of "/EHa" flag to CMakeLists.txt, where other MSVC-specific flags are processed. This also further prepares the removal of redundant cflags setup in Python build scripts.
Pull Request resolved: pytorch/pytorch#23455

Differential Revision: D16542274

Pulled By: ezyang

fbshipit-source-id: 4d3b8b07161478bbba8a21feb6ea24c9024e21ac

CMakeLists.txt

@@ -166,14 +166,18 @@ option(BUILDING_WITH_TORCH_LIBS "Tell cmake if Caffe2 is being built alongside t
 # When generating debug symbols, CMake default to use the flag /Zi.
 # However, it is not compatible with sccache. So we rewrite it off.
 # But some users don't use sccache; this override is for them.
-option(MSVC_Z7_OVERRIDE "Work around sccache bug by replacing /Zi and /ZI with /Z7 when using MSVC (if you are not using sccache, you can turn this OFF)" ON)
+cmake_dependent_option(
+  MSVC_Z7_OVERRIDE "Work around sccache bug by replacing /Zi and /ZI with /Z7 when using MSVC (if you are not using sccache, you can turn this OFF)" ON
+  "MSVC" OFF)
 
 set(ONNX_NAMESPACE "onnx_torch" CACHE STRING "A namespace for ONNX; needed to build with other frameworks that share ONNX.")
 
 # For MSVC,
 # 1. Replace /Zi and /ZI with /Z7
 # 2. Switch off incremental linking in debug builds
 if (MSVC)
+  string(APPEND CMAKE_C_FLAGS " /EHa")
+  string(APPEND CMAKE_CXX_FLAGS " /EHa")
   if(MSVC_Z7_OVERRIDE)
     foreach(flag_var
         CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_DEBUG CMAKE_CXX_FLAGS_RELEASE

tools/setup_helpers/cmake.py

@@ -189,10 +189,6 @@ def generate(self, version, cmake_python_library, build_python, build_test, my_e
 
         cflags = os.getenv('CFLAGS', "") + " " + os.getenv('CPPFLAGS', "")
         ldflags = os.getenv('LDFLAGS', "")
-        if IS_WINDOWS:
-            CMake.defines(args, MSVC_Z7_OVERRIDE=not check_negative_env_flag(
-                'MSVC_Z7_OVERRIDE'))
-            cflags += " /EHa"
 
         base_dir = os.path.dirname(os.path.dirname(os.path.dirname(
             os.path.abspath(__file__))))
@@ -227,6 +223,7 @@ def generate(self, version, cmake_python_library, build_python, build_test, my_e
              'EXPERIMENTAL_SINGLE_THREAD_POOL',
              'MKL_THREADING',
              'MKLDNN_THREADING',
+             'MSVC_Z7_OVERRIDE',
              'ONNX_ML',
              'ONNX_NAMESPACE',
              'ATEN_THREADING',