Index: clang/CMakeLists.txt
===================================================================
--- clang/CMakeLists.txt
+++ clang/CMakeLists.txt
@@ -212,6 +212,9 @@
 set(ENABLE_X86_RELAX_RELOCATIONS OFF CACHE BOOL
     "enable x86 relax relocations by default")
 
+set(ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER FALSE CACHE BOOL
+  "Enable the experimental new pass manager by default.")
+
 # TODO: verify the values against LangStandards.def?
 set(CLANG_DEFAULT_STD_C "" CACHE STRING
   "Default standard to use for C/ObjC code (IDENT from LangStandards.def, empty for platform default)")
Index: clang/include/clang/Config/config.h.cmake
===================================================================
--- clang/include/clang/Config/config.h.cmake
+++ clang/include/clang/Config/config.h.cmake
@@ -72,6 +72,9 @@
 /* enable x86 relax relocations by default */
 #cmakedefine01 ENABLE_X86_RELAX_RELOCATIONS
 
+/* Enable the experimental new pass manager by default */
+#cmakedefine01 ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER
+
 /* Enable each functionality of modules */
 #cmakedefine01 CLANG_ENABLE_ARCMT
 #cmakedefine01 CLANG_ENABLE_OBJC_REWRITER
Index: clang/lib/Driver/ToolChains/CommonArgs.cpp
===================================================================
--- clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -455,7 +455,7 @@
   // Need this flag to turn on new pass manager via Gold plugin.
   if (Args.hasFlag(options::OPT_fexperimental_new_pass_manager,
                    options::OPT_fno_experimental_new_pass_manager,
-                   /* Default */ false)) {
+                   /* Default */ ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER)) {
     CmdArgs.push_back("-plugin-opt=new-pass-manager");
   }
 
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -490,7 +490,7 @@
 
   Opts.ExperimentalNewPassManager = Args.hasFlag(
       OPT_fexperimental_new_pass_manager, OPT_fno_experimental_new_pass_manager,
-      /* Default */ false);
+      /* Default */ ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER);
 
   Opts.DebugPassManager =
       Args.hasFlag(OPT_fdebug_pass_manager, OPT_fno_debug_pass_manager,