CMake: Windows: clang-cl fixes

Support for building blender with clang on windows on x64 was added
years ago but given there are no active users support has crumbled a
bit.

This PR brings the build system back into working order but upstream
patches in openVDB are still required for a successful build see PR
#120317 for details.

Blender when build with clang the classroom scenes rendered on the cpu
with cycles is seeing a 5% reduction in render time on both an
AMD 7700x and an Intel 14900k.

build_files/windows/configure_msbuild.cmd

@@ -8,7 +8,7 @@ if "%BUILD_WITH_SCCACHE%"=="1" (
 )
 
 if "%WITH_CLANG%"=="1" (
-	set CLANG_CMAKE_ARGS=-T"llvm"
+	set CLANG_CMAKE_ARGS=-T"ClangCl"
 )
 
 if "%WITH_ASAN%"=="1" (

intern/cycles/CMakeLists.txt

@@ -122,11 +122,23 @@ elseif(CMAKE_COMPILER_IS_GNUCC OR (CMAKE_CXX_COMPILER_ID MATCHES "Clang"))
   check_cxx_compiler_flag(-mavx2 CXX_HAS_AVX2)
 
   # Assume no signal trapping for better code generation.
-  set(CYCLES_KERNEL_FLAGS "-fno-trapping-math")
-  # Avoid overhead of setting errno for NaNs.
-  string(APPEND CYCLES_KERNEL_FLAGS " -fno-math-errno")
-  # Let compiler optimize 0.0 - x without worrying about signed zeros.
-  string(APPEND CYCLES_KERNEL_FLAGS " -fno-signed-zeros")
+  # We need to omit or modify specific flags to pass through clang-cl to prevent
+  # unknown flag errors
+  if (WIN32 AND MSVC)
+    # Pass clang flags directly to clang otherwise. Clang-cl doesn't recognize
+    # these flags by default
+    set(CYCLES_KERNEL_FLAGS " /clang:-fno-trapping-math")
+    # Avoid overhead of setting errno for NaNs.
+    string(APPEND CYCLES_KERNEL_FLAGS " /clang:-fno-math-errno")
+    # Let compiler optimize 0.0 - x without worrying about signed zeros.
+    string(APPEND CYCLES_KERNEL_FLAGS " /clang:-fno-signed-zeros")
+  else ()
+    set(CYCLES_KERNEL_FLAGS " -fno-trapping-math")
+    # Avoid overhead of setting errno for NaNs.
+    string(APPEND CYCLES_KERNEL_FLAGS " -fno-math-errno")
+    # Let compiler optimize 0.0 - x without worrying about signed zeros.
+    string(APPEND CYCLES_KERNEL_FLAGS " -fno-signed-zeros")
+  endif()
 
   if(CMAKE_COMPILER_IS_GNUCC)
     # Assume no signal trapping for better code generation.

source/blender/blenlib/BLI_utildefines.h

@@ -676,7 +676,7 @@ extern bool BLI_memory_is_zero(const void *arr, size_t arr_size);
  */
 #define BLI_ENABLE_IF(condition) typename std::enable_if_t<(condition)> * = nullptr
 
-#if defined(_MSC_VER)
+#if defined(_MSC_VER) && !defined(__clang__)
 #  define BLI_NO_UNIQUE_ADDRESS [[msvc::no_unique_address]]
 #elif defined(__has_cpp_attribute)
 #  if __has_cpp_attribute(no_unique_address)

source/blender/blenlib/intern/task_pool.cc

@@ -78,7 +78,10 @@ class Task {
     other.freedata = nullptr;
   }
 
-#if defined(WITH_TBB) && TBB_INTERFACE_VERSION_MAJOR < 10
+// TBB has a check in tbb/include/task_group.h where __TBB_CPP11_RVALUE_REF_PRESENT should evaluate to true as with
+// the other MSVC build. However, because of the clang compiler it does not and we attempt to call a deleted constructor
+// in the tbb_task_pool_run function. This check fixes this issue and keeps our Task constructor valid
+#if (defined(WITH_TBB) && TBB_INTERFACE_VERSION_MAJOR < 10) || (defined(_MSC_VER) && defined(__clang__) && TBB_INTERFACE_VERSION_MAJOR < 12)
   Task(const Task &other)
       : pool(other.pool),
         run(other.run),

source/blender/editors/sculpt_paint/CMakeLists.txt

@@ -133,7 +133,12 @@ if(WITH_GTESTS)
   blender_add_test_suite_lib(editor_sculpt_paint "${TEST_SRC}" "${INC};${TEST_INC}" "${INC_SYS}" "${TEST_LIB}")
 endif()
 
-blender_add_lib(bf_editor_sculpt_paint "${SRC}" "${INC}" "${INC_SYS}" "${LIB}")
+# If compiling with msvc clang we need to add the D_LIBCPP_VERSION define
+# so we don't run into tbb errors when compiling with lib
+if(WITH_TBB AND MSVC_CLANG)
+  string(APPEND CMAKE_CXX_FLAGS " /D_LIBCPP_VERSION")
+endif()
 
+blender_add_lib(bf_editor_sculpt_paint "${SRC}" "${INC}" "${INC_SYS}" "${LIB}")
 # RNA_prototypes.h
 add_dependencies(bf_editor_sculpt_paint bf_rna)

source/blender/nodes/geometry/CMakeLists.txt

@@ -296,6 +296,13 @@ list(APPEND LIB
   bf_nodes_geometry_generated
 )
 
+# If compiling with msvc clang we need to add the D_LIBCPP_VERSION define
+# so we don't run into tbb errors when compiling with lib
+if(WITH_TBB AND MSVC_CLANG)
+  string(APPEND CMAKE_CXX_FLAGS " /D_LIBCPP_VERSION")
+endif()
+
+
 blender_add_lib(bf_nodes_geometry "${SRC}" "${INC}" "${INC_SYS}" "${LIB}")
 target_link_libraries(bf_nodes_geometry_generated bf_nodes_geometry)
 

source/creator/CMakeLists.txt

@@ -1118,7 +1118,9 @@ elseif(WIN32)
   )
 
   if(WITH_WINDOWS_RELEASE_PDB)
-    if(WITH_WINDOWS_RELEASE_STRIPPED_PDB)
+    # Skip install of stripped pdb if compiling with clang since there doesn't seem
+    # to be a pdbstripped version for clang-cl
+    if(WITH_WINDOWS_RELEASE_STRIPPED_PDB AND NOT MSVC_CLANG)
       # Icky hack for older CMAKE from https://stackoverflow.com/a/21198501
       # `$<CONFIG>` will work in newer CMAKE but the version currently (3.12)
       # on the build-bot does not support this endeavor.
@@ -1851,7 +1853,8 @@ if(WIN32)
     PDB_NAME "blender_private"
     PDB_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/$<CONFIG>"
   )
-  if(WITH_WINDOWS_RELEASE_PDB AND WITH_WINDOWS_RELEASE_STRIPPED_PDB)
+  # If compiling with clang-cl we skip PDBSTRIPPED. There's doesn't seem to be a switch for it currently
+  if(WITH_WINDOWS_RELEASE_PDB AND WITH_WINDOWS_RELEASE_STRIPPED_PDB AND NOT MSVC_CLANG)
     # This is slightly messy, but single target generators like ninja will not have the
     # `CMAKE_CFG_INTDIR` variable and multi-target generators like `msbuild` will not have
     # `CMAKE_BUILD_TYPE`. This can be simplified by `target_link_options` and the `$<CONFIG>`