From 251d64ebd8b3034c674444ca7a72b0c8a3493305 Mon Sep 17 00:00:00 2001
From: Mike Smith <mango@live.cn>
Date: Mon, 6 Jan 2025 13:49:42 +0800
Subject: [PATCH] minor

---
 src/backends/fallback/CMakeLists.txt | 62 +++++++++++++++++-----------
 1 file changed, 39 insertions(+), 23 deletions(-)

diff --git a/src/backends/fallback/CMakeLists.txt b/src/backends/fallback/CMakeLists.txt
index 787612550..bcfe80672 100644
--- a/src/backends/fallback/CMakeLists.txt
+++ b/src/backends/fallback/CMakeLists.txt
@@ -10,6 +10,9 @@ if (NOT LLVM_FOUND)
 endif ()
 
 if (LLVM_FOUND AND embree_FOUND)
+
+    message(STATUS "Build with fallback backend (LLVM ${LLVM_VERSION}, Embree ${embree_VERSION})")
+
     set(LUISA_COMPUTE_ENABLE_FALLBACK ON)
     set(LC_BACKEND_FALLBACK_SRC
             fallback_device.cpp
@@ -34,8 +37,38 @@ if (LLVM_FOUND AND embree_FOUND)
     # exclude codegen from unity build since it's too big
     set_source_files_properties(fallback_codegen.cpp PROPERTIES UNITY_BUILD OFF)
     target_link_directories(luisa-compute-backend-fallback PRIVATE ${LLVM_LIBRARY_DIRS})
+    target_link_libraries(luisa-compute-backend-fallback PRIVATE
+            luisa-compute-xir
+            luisa-compute-vulkan-swapchain
+            embree)
+
+    # help distinguish between embree 3 and 4
+    target_compile_definitions(luisa-compute-backend-fallback PRIVATE
+            LUISA_COMPUTE_EMBREE_VERSION=${embree_VERSION_MAJOR})
 
     # use libdispatch or TBB for parallel_for on non-Apple Unix systems if available
+    if (UNIX AND NOT APPLE)
+        # libdispatch
+        find_library(DISPATCH_LIB dispatch)
+        find_path(DISPATCH_INCLUDE_DIR dispatch/dispatch.h)
+        if (DISPATCH_LIB AND DISPATCH_INCLUDE_DIR)
+            target_compile_definitions(luisa-compute-backend-fallback PRIVATE LUISA_COMPUTE_ENABLE_LIBDISPATCH=1)
+            target_link_libraries(luisa-compute-backend-fallback PRIVATE ${DISPATCH_LIB})
+            target_include_directories(luisa-compute-backend-fallback PRIVATE ${DISPATCH_INCLUDE_DIR})
+        else ()
+            find_package(TBB CONFIG)
+            if (TBB_FOUND)
+                target_compile_definitions(luisa-compute-backend-fallback PRIVATE LUISA_COMPUTE_ENABLE_TBB=1)
+                target_link_libraries(luisa-compute-backend-fallback PRIVATE TBB::tbb)
+            else ()
+                message(WARNING "TBB and libdispatch not found. Performance of the fallback backend may be affected.")
+            endif ()
+        endif ()
+    endif ()
+
+    # LLVM
+    target_include_directories(luisa-compute-backend-fallback PRIVATE ${LLVM_INCLUDE_DIRS})
+    llvm_map_components_to_libnames(LLVM_LIBS core executionengine support orcjit nativecodegen irreader passes analysis coroutines)
     if (UNIX AND NOT APPLE)
         # check if the libraries exist
         # map library dirs to link directories options
@@ -63,37 +96,20 @@ if (LLVM_FOUND AND embree_FOUND)
                 set(LLVM_LIBS ${LLVM_DYLIB})
             endif ()
         endif ()
+        # avoid re-exporting symbols from LLVM
+        target_link_libraries(luisa-compute-backend-fallback PRIVATE "-Wl,--exclude-libs,ALL" ${LLVM_LIBS})
+    else ()
+        target_link_libraries(luisa-compute-backend-fallback PRIVATE ${LLVM_LIBS})
     endif ()
 
-    message(STATUS "Build with fallback backend (LLVM ${LLVM_VERSION}, Embree ${embree_VERSION})")
-    llvm_map_components_to_libnames(LLVM_LIBS core executionengine support orcjit nativecodegen irreader passes analysis coroutines)
-    if (UNIX AND NOT APPLE)
-        # check if the libraries exist
-        try_compile(LLVM_LIBS_EXIST
-                SOURCE_FROM_CONTENT "try_link_llvm.cpp" "int main() {}"
-                LINK_LIBRARIES ${LLVM_LIBS})
-        if (NOT LLVM_LIBS_EXIST)
-            message(WARNING "LLVM libraries not found. Trying to link with LLVM shared libraries.")
-            find_library(LLVM_DYLIB LLVM REQUIRED)
-            message(STATUS "LLVM libraries found at ${LLVM_DYLIB}")
-            set(LLVM_LIBS ${LLVM_DYLIB})
-        endif ()
-    endif ()
-    target_include_directories(luisa-compute-backend-fallback PRIVATE ${LLVM_INCLUDE_DIRS})
-    target_link_libraries(luisa-compute-backend-fallback PRIVATE
-            embree ${LLVM_LIBS}
-            luisa-compute-xir
-            luisa-compute-vulkan-swapchain)
     if (CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
         target_compile_options(luisa-compute-backend-fallback PRIVATE
                 /wd4624 /wd4996 # do not complain about LLVM
-                /fp:fast /fp:contract /fp:except-)
+                /fp:fast /fp:contract /fp:except- /ARCH:AVX2)
     else ()
         target_compile_options(luisa-compute-backend-fallback PRIVATE -ffast-math)
     endif ()
-    # help distinguish between embree 3 and 4
-    target_compile_definitions(luisa-compute-backend-fallback PRIVATE
-            LUISA_COMPUTE_EMBREE_VERSION=${embree_VERSION_MAJOR})
+
 elseif (NOT LUISA_COMPUTE_CHECK_BACKEND_DEPENDENCIES)
     message(FATAL_ERROR "LLVM or Embree not found for the fallback backend.")
 else ()