Adding file checks to rebuild sources if they're empty

Author: BujSet

tools/cmake/Codegen.cmake

@@ -245,15 +245,27 @@ function(gen_operators_lib)
         list(REMOVE_ITEM GEN_KERNEL_LIBS ${portable_kernels_check})
 
         # Build kernels_util_all_deps, since later selected_portable_kernels depends on it
-        list(TRANSFORM _kernels_util_all_deps__srcs PREPEND "${EXECUTORCH_ROOT}/")
+	list(LENGTH  _kernels_util_all_deps__srcs num_util_srcs)
+	if(num_util_srcs EQUAL 0)
+            file(GLOB_RECURSE _kernels_util_all_deps__srcs  "${EXECUTORCH_DIR}/kernels/portable/cpu/util/*.cpp")
+            list(FILTER _kernels_util_all_deps__srcs EXCLUDE REGEX "${EXECUTORCH_DIR}/kernels/portable/cpu/util/test/.*")
+        else()
+            list(TRANSFORM _kernels_util_all_deps__srcs PREPEND "${EXECUTORCH_ROOT}/")
+        endif()
         add_library(selected_kernels_util_all_deps ${_kernels_util_all_deps__srcs})
         target_link_libraries(selected_kernels_util_all_deps PRIVATE executorch_core)
         target_include_directories(selected_kernels_util_all_deps PUBLIC ${_common_include_directories})
         target_compile_definitions(selected_kernels_util_all_deps PUBLIC C10_USING_CUSTOM_GENERATED_MACROS)
         target_compile_options(selected_kernels_util_all_deps PUBLIC ${_common_compile_options})
 
         # Build selected_portable_kernels
-        list(TRANSFORM _portable_kernels__srcs PREPEND "${EXECUTORCH_ROOT}/")
+	list(LENGTH  _portable_kernels__srcs num_kernel_srcs)
+	if(num_kernel_srcs EQUAL 0)
+            file(GLOB_RECURSE _portable_kernels__srcs  "${EXECUTORCH_DIR}/kernels/portable/cpu/op_*.cpp")
+            list(FILTER _portable_kernels__srcs EXCLUDE REGEX "${EXECUTORCH_DIR}/kernels/portable/cpu/util/test/.*")
+        else()
+            list(TRANSFORM _portable_kernels__srcs PREPEND "${EXECUTORCH_ROOT}/")
+        endif()
         add_library(selected_portable_kernels ${_portable_kernels__srcs})
         target_link_libraries(selected_portable_kernels PRIVATE executorch_core selected_kernels_util_all_deps)
         target_compile_options(selected_portable_kernels PUBLIC ${_common_compile_options})