Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -2855,6 +2855,13 @@
 def fno_integrated_as : Flag<["-"], "fno-integrated-as">,
                         Flags<[CC1Option, DriverOption]>, Group<f_Group>,
                         HelpText<"Disable the integrated assembler">;
+
+def fintegrated_cc1 : Flag<["-"], "fintegrated-cc1">, Flags<[DriverOption]>,
+                     Group<f_Group>, HelpText<"Run cc1 in-process">;
+def fno_integrated_cc1 : Flag<["-"], "fno-integrated-cc1">,
+                         Flags<[DriverOption]>, Group<f_Group>,
+                         HelpText<"Spawn a separate process for each cc1">;
+
 def : Flag<["-"], "integrated-as">, Alias<fintegrated_as>, Flags<[DriverOption]>;
 def : Flag<["-"], "no-integrated-as">, Alias<fno_integrated_as>,
       Flags<[CC1Option, DriverOption]>;
Index: clang/lib/Driver/Driver.cpp
===================================================================
--- clang/lib/Driver/Driver.cpp
+++ clang/lib/Driver/Driver.cpp
@@ -1035,6 +1035,10 @@
   // -no-canonical-prefixes is used very early in main.
   Args.ClaimAllArgs(options::OPT_no_canonical_prefixes);
 
+  // f(no-)integated-cc1 is also used very early in main.
+  Args.ClaimAllArgs(options::OPT_fintegrated_cc1);
+  Args.ClaimAllArgs(options::OPT_fno_integrated_cc1);
+
   // Ignore -pipe.
   Args.ClaimAllArgs(options::OPT_pipe);
 
Index: clang/test/Driver/cc1-spawnprocess.c
===================================================================
--- clang/test/Driver/cc1-spawnprocess.c
+++ clang/test/Driver/cc1-spawnprocess.c
@@ -1,4 +1,5 @@
-// RUN: env CLANG_SPAWN_CC1= %clang -S %s -o /dev/null
-// RUN: env CLANG_SPAWN_CC1=0 %clang -S %s -o /dev/null
-// RUN: env CLANG_SPAWN_CC1=1 %clang -S %s -o /dev/null
-// RUN: env CLANG_SPAWN_CC1=test not %clang -S %s -o /dev/null
+// RUN: %clang -fintegrated-cc1 %s -### 2>&1 | FileCheck %s --check-prefix=YES
+// RUN: %clang -fno-integrated-cc1 %s -### 2>&1 | FileCheck %s --check-prefix=NO
+
+// YES: (in-process)
+// NO-NOT: (in-process)
Index: clang/tools/driver/driver.cpp
===================================================================
--- clang/tools/driver/driver.cpp
+++ clang/tools/driver/driver.cpp
@@ -258,27 +258,6 @@
   TheDriver.CCLogDiagnostics = !!::getenv("CC_LOG_DIAGNOSTICS");
   if (TheDriver.CCLogDiagnostics)
     TheDriver.CCLogDiagnosticsFilename = ::getenv("CC_LOG_DIAGNOSTICS_FILE");
-
-  // Whether the cc1 tool should be called inside the current process, or if we
-  // should spawn a new clang process (old behavior).
-  // Not having an additional process saves some execution time of Windows,
-  // and makes debugging easier.
-  bool UseNewCC1Process = CLANG_SPAWN_CC1;
-
-  StringRef SpawnCC1Str = ::getenv("CLANG_SPAWN_CC1");
-  if (!SpawnCC1Str.empty()) {
-    if (SpawnCC1Str != "0" && SpawnCC1Str != "1") {
-      llvm::errs() << "error: the value of the environment variable "
-                      "CLANG_SPAWN_CC1 must be either 0 or 1.\n";
-      ::exit(1);
-    }
-    UseNewCC1Process = SpawnCC1Str[0] - '0';
-  }
-  if (!UseNewCC1Process) {
-    TheDriver.CC1Main = &ExecuteCC1Tool;
-    // Ensure the CC1Command actually catches cc1 crashes
-    llvm::CrashRecoveryContext::Enable();
-  }
 }
 
 static void FixupDiagPrefixExeName(TextDiagnosticPrinter *DiagClient,
@@ -330,7 +309,7 @@
 
 static int ExecuteCC1Tool(ArrayRef<const char *> argv) {
   // If we call the cc1 tool from the clangDriver library (through
-  // Driver::CC1Main), we need to cleanup the options usage count. The options
+  // 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();
@@ -413,14 +392,26 @@
     return ExecuteCC1Tool(argv);
   }
 
+  // Handle options that need handling before the real command line parsing in
+  // Driver::BuildCompilation()
   bool CanonicalPrefixes = true;
+
+  // Whether the cc1 tool should be called inside the current process, or if we
+  // should spawn a new clang subprocess (old behavior).
+  // Not having an additional process saves some execution time of Windows,
+  // and makes debugging and profiling easier.
+  bool UseNewCC1Process = CLANG_SPAWN_CC1;
+
   for (int i = 1, size = argv.size(); i < size; ++i) {
     // Skip end-of-line response file markers
     if (argv[i] == nullptr)
       continue;
     if (StringRef(argv[i]) == "-no-canonical-prefixes") {
       CanonicalPrefixes = false;
-      break;
+    } else if (StringRef(argv[i]) == "-fno-integrated-cc1") {
+      UseNewCC1Process = true;
+    } else if (StringRef(argv[i]) == "-fintegrated-cc1") {
+      UseNewCC1Process = false;
     }
   }
 
@@ -486,6 +477,12 @@
 
   SetBackdoorDriverOutputsFromEnvVars(TheDriver);
 
+  if (!UseNewCC1Process) {
+    TheDriver.CC1Main = &ExecuteCC1Tool;
+    // Ensure the CC1Command actually catches cc1 crashes
+    llvm::CrashRecoveryContext::Enable();
+  }
+
   std::unique_ptr<Compilation> C(TheDriver.BuildCompilation(argv));
   int Res = 1;
   if (C && !C->containsError()) {