Index: llvm/cmake/modules/HandleLLVMOptions.cmake
===================================================================
--- llvm/cmake/modules/HandleLLVMOptions.cmake
+++ llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -793,6 +793,10 @@
     endif()
     add_flag_if_supported("-fdata-sections" FDATA_SECTIONS)
   endif()
+elseif(MSVC)
+  if( NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG" )
+    append("/Gw" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  endif()
 endif()
 
 if(MSVC)
Index: llvm/utils/gn/build/BUILD.gn
===================================================================
--- llvm/utils/gn/build/BUILD.gn
+++ llvm/utils/gn/build/BUILD.gn
@@ -59,8 +59,8 @@
     }
     if (is_optimized) {
       cflags += [
-        # FIXME: evaluate /Gw (not part of /O2)
         "/O2",
+        "/Gw",
         "/Zc:inline",
       ]
       ldflags += [