Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -7327,6 +7327,14 @@
     CmdArgs.push_back("--dependent-lib=oldnames");
   }
 
+  // Starting with VS 2022 17.1, MSVC predefines the below macro to inform
+  // users of the execution character set defined at compile time.
+  // The value given is the Windows Code Page Identifier:
+  // https://docs.microsoft.com/en-us/windows/win32/intl/code-page-identifiers
+  //
+  // Clang currently only supports UTF-8, so we'll use 65001
+  CmdArgs.push_back("-D_MSVC_EXECUTION_CHARACTER_SET=65001");
+
   if (Arg *ShowIncludes =
           Args.getLastArg(options::OPT__SLASH_showIncludes,
                           options::OPT__SLASH_showIncludes_user)) {
Index: clang/test/Driver/cl-execution-character-set.c
===================================================================
--- /dev/null
+++ clang/test/Driver/cl-execution-character-set.c
@@ -0,0 +1,7 @@
+// Note: %s must be preceded by --, otherwise it may be interpreted as a
+// command-line option, e.g. on Mac where %s is commonly under /Users.
+
+// Only UTF-8 is currently supported, which has the Windows Code
+// Page Identifier 65001
+// RUN: %clang_cl -### -- %s 2>&1 | FileCheck %s
+// CHECK: -D_MSVC_EXECUTION_CHARACTER_SET=65001