[build] Warning Suppression PR #1: Turned on -Wno-ignored-attributes …

…& Removed unused functions (#4916)

cmake/TaichiCXXFlags.cmake

@@ -46,7 +46,25 @@ else()
         message("Invalid compiler ${CMAKE_CXX_COMPILER_ID} detected.")
         message(FATAL_ERROR "clang and MSVC are the only supported compilers for Taichi compiler development. Consider using 'cmake -DCMAKE_CXX_COMPILER=clang' if you are on Linux.")
     endif()
+
+    # [Global] CXX compilation option to enable all warnings.
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall ")
+
+    # [Global] By default, CXX compiler will throw a warning if it decides to ignore an attribute, for example "[[ maybe unused ]]".
+    # However, this behaviour diverges across different compilers (GCC/CLANG), as well as different compiler versions.
+    # Therefore we disable such warnings for now.
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-ignored-attributes ")
+
+    # [Global] Clang warns if a C++ pointer's nullability wasn't marked explicitly (__nonnull, nullable, ...).
+    # Nullability seems to be a clang-specific feature, thus we disable this warning.
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-nullability-completeness ")
+
+    # [Global] Disable warning for unused-private-field for convenience in development.
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unused-private-field ")
+
+    # [Global] By evaluating "constexpr", compiler throws a warning for functions known to be dead at compile time.
+    # However, some of these "constexpr" are debug flags and will be manually enabled upon debuging.
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unneeded-internal-declaration ")
 endif ()
 
 message("Building for processor ${CMAKE_SYSTEM_PROCESSOR}")

taichi/backends/interop/vulkan_cpu_interop.cpp

@@ -22,7 +22,6 @@ void memcpy_cpu_to_vulkan_via_staging(DevicePtr dst,
   VulkanDevice *vk_dev = dynamic_cast<VulkanDevice *>(dst.device);
   CpuDevice *cpu_dev = dynamic_cast<CpuDevice *>(src.device);
 
-  DeviceAllocation dst_alloc(dst);
   DeviceAllocation src_alloc(src);
 
   CpuDevice::AllocInfo src_alloc_info = cpu_dev->get_alloc_info(src_alloc);

taichi/backends/vulkan/vulkan_program.cpp

@@ -71,8 +71,8 @@ FunctionType compile_to_executable(Kernel *kernel,
                                    VkRuntime *runtime,
                                    SNodeTreeManager *snode_tree_mgr) {
   auto handle = runtime->register_taichi_kernel(
-      std::move(run_codegen(kernel, runtime->get_ti_device(),
-                            snode_tree_mgr->get_compiled_structs())));
+      run_codegen(kernel, runtime->get_ti_device(),
+                  snode_tree_mgr->get_compiled_structs()));
   return [runtime, handle](RuntimeContext &ctx) {
     runtime->launch_kernel(handle, &ctx);
   };