diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -758,6 +758,16 @@
 
   # Enable -Wstring-conversion to catch misuse of string literals.
   add_flag_if_supported("-Wstring-conversion" STRING_CONVERSION_FLAG)
+
+  # Disabled for gcc. Clang and gcc differ in handling of switch statements
+  # that exhaustively handle all enumerations. This diagnostic is emitted by
+  # gcc in such cases, while clang does not. For gcc, exhaustive switch
+  # statements must be followed by a return statement or llvm_unreachable().
+  if (NOT CMAKE_COMPILER_IS_GNUCXX)
+    # Enable -Werror=return-type if available, to catch functions that contain
+    # control paths that do not return a value.
+    add_flag_if_supported("-Werror=return-type" WERROR_RETURN_TYPE)
+  endif()
 endif (LLVM_ENABLE_WARNINGS AND (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL))
 
 if (LLVM_COMPILER_IS_GCC_COMPATIBLE AND NOT LLVM_ENABLE_WARNINGS)