Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -6695,6 +6695,8 @@
 def _SLASH_QIntel_jcc_erratum : CLFlag<"QIntel-jcc-erratum">,
   HelpText<"Align branches within 32-byte boundaries to mitigate the performance impact of the Intel JCC erratum.">,
   Alias<mbranches_within_32B_boundaries>;
+def _SLASH_arm64EC : CLFlag<"arm64EC">,
+  HelpText<"Set build target to arm64ec">;
 
 // Non-aliases:
 
Index: clang/lib/Driver/Driver.cpp
===================================================================
--- clang/lib/Driver/Driver.cpp
+++ clang/lib/Driver/Driver.cpp
@@ -1252,6 +1252,8 @@
     T.setVendor(llvm::Triple::PC);
     T.setEnvironment(llvm::Triple::MSVC);
     T.setObjectFormat(llvm::Triple::COFF);
+    if (Args.hasArg(options::OPT__SLASH_arm64EC))
+      T.setArch(llvm::Triple::aarch64, llvm::Triple::AArch64SubArch_arm64ec);
     TargetTriple = T.str();
   } else if (IsDXCMode()) {
     // Build TargetTriple from target_profile option for clang-dxc.
Index: clang/test/Driver/cl-options.c
===================================================================
--- clang/test/Driver/cl-options.c
+++ clang/test/Driver/cl-options.c
@@ -783,4 +783,7 @@
 // EXTERNAL_W0: "-Wno-system-headers"
 // EXTERNAL_Wn: "-Wsystem-headers"
 
+// RUN: %clang_cl -vctoolsdir "" /arm64EC /c -### -- %s 2>&1 | FileCheck %s --check-prefix ARM64EC
+// ARM64EC: "-triple" "arm64ec-pc-windows-msvc19.20.0"
+
 void f(void) { }