Windows: Enable clang-cl for ARM64

This gets Windows ARM64 to compile with clang-cl, which gives up to 40% performance improvements in certain scenes rendered with cycles, compared to MSVC.

This is all tested using LLVM 18.1.8 and a VS2022 `vcvarsall` window.

Subsequent PRs with various lib version updates, etc to go in at a later point.

Pull Request: https://projects.blender.org/blender/blender/pulls/124182

CMakeLists.txt

@@ -410,6 +410,10 @@ option(WITH_OPENMP "Enable OpenMP (has to be supported by the compiler)" ON)
 if(UNIX AND NOT APPLE)
   option(WITH_OPENMP_STATIC "Link OpenMP statically (only used by the release environment)" OFF)
   mark_as_advanced(WITH_OPENMP_STATIC)
+elseif(WIN32 AND CMAKE_C_COMPILER_ID MATCHES "Clang" AND CMAKE_SYSTEM_PROCESSOR STREQUAL "ARM64")
+  # At time of testing (LLVM 18.1.6) OMP is not included in public LLVM builds for Windows ARM64
+  set(WITH_OPENMP OFF)
+  set(WITH_OPENMP_STATIC OFF)
 endif()
 
 if(WITH_GHOST_X11)
@@ -2167,6 +2171,9 @@ elseif(CMAKE_C_COMPILER_ID MATCHES "Clang")
       C_WARN_CLANG_CL_BITFIELD_ENUM_CONVERSION -Wno-bitfield-enum-conversion # 1
       C_WARN_CLANG_CL_UNUSED_LAMBDA_CAPTURE -Wno-unused-lambda-capture # 1
       C_WARN_CLANG_CL_SHADOW_FIELD_IN_CONSTRUCTOR_MODIFIED -Wno-shadow-field-in-constructor-modified # 1
+      # And some additional ones that came up when using LLVM 18.1.8 on Windows ARM64
+      C_WARN_CLANG_CL_SWITCH_DEFAULT -Wno-switch-default
+      C_WARN_CLANG_CL_NAN_INFINITY_DISABLED -Wno-nan-infinity-disabled
     )
 
   add_check_cxx_compiler_flags(
@@ -2298,6 +2305,9 @@ elseif(CMAKE_C_COMPILER_ID MATCHES "Clang")
       CXX_WARN_CLANG_CL_BITFIELD_ENUM_CONVERSION -Wno-bitfield-enum-conversion # 1
       CXX_WARN_CLANG_CL_UNUSED_LAMBDA_CAPTURE -Wno-unused-lambda-capture # 1
       CXX_WARN_CLANG_CL_SHADOW_FIELD_IN_CONSTRUCTOR_MODIFIED -Wno-shadow-field-in-constructor-modified # 1
+      # And some additional ones that came up when using LLVM 18.1.8 on Windows ARM64
+      CXX_WARN_CLANG_CL_SWITCH_DEFAULT -Wno-switch-default
+      CXX_WARN_CLANG_CL_NAN_INFINITY_DISABLED -Wno-nan-infinity-disabled
     )
   endif()
 

build_files/cmake/platform/platform_win32.cmake

@@ -180,8 +180,8 @@ remove_cc_flag(
 )
 
 if(MSVC_CLANG) # Clangs version of cl doesn't support all flags
-  string(APPEND CMAKE_CXX_FLAGS " ${CXX_WARN_FLAGS} /nologo /J /Gd /EHsc -Wno-unused-command-line-argument -Wno-microsoft-enum-forward-reference ")
+  string(APPEND CMAKE_CXX_FLAGS " ${CXX_WARN_FLAGS} /nologo /J /Gd /EHsc -Wno-unused-command-line-argument -Wno-microsoft-enum-forward-reference /clang:-funsigned-char /clang:-fno-strict-aliasing /clang:-ffp-contract=off")
-  string(APPEND CMAKE_C_FLAGS   " /nologo /J /Gd -Wno-unused-command-line-argument -Wno-microsoft-enum-forward-reference")
+  string(APPEND CMAKE_C_FLAGS   " /nologo /J /Gd -Wno-unused-command-line-argument -Wno-microsoft-enum-forward-reference /clang:-funsigned-char /clang:-fno-strict-aliasing /clang:-ffp-contract=off")
 else()
   string(APPEND CMAKE_CXX_FLAGS " /nologo /J /Gd /MP /EHsc /bigobj")
   string(APPEND CMAKE_C_FLAGS   " /nologo /J /Gd /MP /bigobj")

build_files/windows/configure_ninja.cmd

@@ -37,9 +37,14 @@ set LLVM_DIR=
 :DetectionComplete	
 	set CC=%LLVM_DIR%\bin\clang-cl
 	set CXX=%LLVM_DIR%\bin\clang-cl
-	rem build and tested against 2019 16.2
+	if "%PROCESSOR_ARCHITECTURE%" == "ARM64" (
-	set CFLAGS=-m64 -fmsc-version=1922
+		set CFLAGS=-m64
-	set CXXFLAGS=-m64 -fmsc-version=1922
+		set CXXFLAGS=-m64
+	) else (
+		rem build and tested against 2019 16.2
+		set CFLAGS=-m64 -fmsc-version=1922
+		set CXXFLAGS=-m64 -fmsc-version=1922
+	)
 )
 
 if "%WITH_ASAN%"=="1" (

extern/lzma/LzFind.c

@@ -625,7 +625,7 @@ void MatchFinder_Init(CMatchFinder *p)
     #endif
   #endif
 
-  #if defined(_MSC_VER) && defined(MY_CPU_ARM64)
+  #if defined(_MSC_VER) && defined(MY_CPU_ARM64) && !defined(__clang__)
     #include <arm64_neon.h>
   #else
     #include <arm_neon.h>

extern/lzma/README.blender

@@ -2,7 +2,8 @@ Project: LZMA SDK
 URL: https://www.7-zip.org/sdk.html
 License: Public Domain
 Upstream version: 23.01
-Local modifications: No code changes
+Local modifications:
+* Update LzFind.c to find the correct NEON header when using clang-cl + Windows ARM64
 
 - Took only files needed for Blender: C source for raw LZMA1 encoder/decoder.
 - CMakeLists.txt is made for Blender codebase

extern/lzma/patches/lzma.diff

@@ -0,0 +1,13 @@
+diff --git a/extern/lzma/LzFind.c b/extern/lzma/LzFind.c
+index 0fbd5aae563..94b4879cfdc 100644
+--- a/extern/lzma/LzFind.c
++++ b/extern/lzma/LzFind.c
+@@ -625,7 +625,7 @@ void MatchFinder_Init(CMatchFinder *p)
+     #endif
+   #endif
+ 
+-  #if defined(_MSC_VER) && defined(MY_CPU_ARM64)
++  #if defined(_MSC_VER) && defined(MY_CPU_ARM64) && !defined(__clang__)
+     #include <arm64_neon.h>
+   #else
+     #include <arm_neon.h>

intern/cycles/CMakeLists.txt

@@ -446,6 +446,8 @@ endif()
 if(WITH_CYCLES_BLENDER)
   # Not needed to make cycles automated tests pass with -march=native.
   # However Blender itself needs this flag.
+  # Note: the clang-cl style removal must go first, to avoid a dangling "/clang:"
+  remove_cc_flag("/clang:-ffp-contract=off")
   remove_cc_flag("-ffp-contract=off")
   add_definitions(-DWITH_BLENDER_GUARDEDALLOC)
   add_subdirectory(blender)