Index: clang/include/clang/Driver/Driver.h
===================================================================
--- clang/include/clang/Driver/Driver.h
+++ clang/include/clang/Driver/Driver.h
@@ -208,7 +208,7 @@
   /// When the clangDriver lib is used through clang.exe, this provides a
   /// shortcut for executing the -cc1 command-line directly, in the same
   /// process.
-  typedef int (*CC1ToolFunc)(ArrayRef<const char *> argv);
+  typedef int (*CC1ToolFunc)(SmallVectorImpl<const char *> &ArgV);
   CC1ToolFunc CC1Main = nullptr;
 
 private:
Index: clang/test/Driver/Wp-args.c
===================================================================
--- clang/test/Driver/Wp-args.c
+++ clang/test/Driver/Wp-args.c
@@ -19,3 +19,9 @@
 // MMD: "-cc1"
 // MMD-NOT: -MMD
 // MMD: "-dependency-file" "Wp-args.d"
+
+// Ensure response files are properly expanded with -Wp
+// RUN: echo -rewrite-macros > %t.rsp
+// RUN: %clang -Wp,@%t.rsp -E %s | FileCheck -check-prefix RSP %s
+
+// RSP: inception
Index: clang/tools/driver/driver.cpp
===================================================================
--- clang/tools/driver/driver.cpp
+++ clang/tools/driver/driver.cpp
@@ -241,8 +241,6 @@
       *NumberSignPtr = '=';
 }
 
-static int ExecuteCC1Tool(ArrayRef<const char *> argv);
-
 static void SetBackdoorDriverOutputsFromEnvVars(Driver &TheDriver) {
   // Handle CC_PRINT_OPTIONS and CC_PRINT_OPTIONS_FILE.
   TheDriver.CCPrintOptions = !!::getenv("CC_PRINT_OPTIONS");
@@ -313,21 +311,27 @@
     TheDriver.setInstalledDir(InstalledPathParent);
 }
 
-static int ExecuteCC1Tool(ArrayRef<const char *> argv) {
+static int ExecuteCC1Tool(SmallVectorImpl<const char *> &ArgV) {
   // If we call the cc1 tool from the clangDriver library (through
   // Driver::CC1Main), we need to clean up the options usage count. The options
   // are currently global, and they might have been used previously by the
   // driver.
   llvm::cl::ResetAllOptionOccurrences();
-  StringRef Tool = argv[1];
-  void *GetExecutablePathVP = (void *)(intptr_t) GetExecutablePath;
+
+  llvm::BumpPtrAllocator A;
+  llvm::StringSaver Saver(A);
+  llvm::cl::ExpandResponseFiles(Saver, &llvm::cl::TokenizeGNUCommandLine, ArgV,
+                                /*MarkEOLs=*/false);
+  StringRef Tool = ArgV[1];
+  void *GetExecutablePathVP = (void *)(intptr_t)GetExecutablePath;
   if (Tool == "-cc1")
-    return cc1_main(argv.slice(2), argv[0], GetExecutablePathVP);
+    return cc1_main(makeArrayRef(ArgV).slice(2), ArgV[0], GetExecutablePathVP);
   if (Tool == "-cc1as")
-    return cc1as_main(argv.slice(2), argv[0], GetExecutablePathVP);
+    return cc1as_main(makeArrayRef(ArgV).slice(2), ArgV[0],
+                      GetExecutablePathVP);
   if (Tool == "-cc1gen-reproducer")
-    return cc1gen_reproducer_main(argv.slice(2), argv[0], GetExecutablePathVP);
-
+    return cc1gen_reproducer_main(makeArrayRef(ArgV).slice(2), ArgV[0],
+                                  GetExecutablePathVP);
   // Reject unknown tools.
   llvm::errs() << "error: unknown integrated tool '" << Tool << "'. "
                << "Valid tools include '-cc1' and '-cc1as'.\n";