Index: include/clang/Driver/CC1Options.td
===================================================================
--- include/clang/Driver/CC1Options.td
+++ include/clang/Driver/CC1Options.td
@@ -157,6 +157,11 @@
   HelpText<"Disable implicit builtin knowledge of math functions">;
 }
 
+def newpm_passes_EQ : Joined<["-"], "newpm-passes=">,
+  HelpText<"Pass pipeline description for new PM">;
+def newpm_aa_pipeline_EQ : Joined<["-"], "newpm-aa-pipeline=">,
+  HelpText<"Alias analysis pipeline for the new PM">;
+
 def disable_llvm_optzns : Flag<["-"], "disable-llvm-optzns">,
   HelpText<"Don't run LLVM optimization passes">;
 def disable_llvm_verifier : Flag<["-"], "disable-llvm-verifier">,
Index: include/clang/Frontend/CodeGenOptions.h
===================================================================
--- include/clang/Frontend/CodeGenOptions.h
+++ include/clang/Frontend/CodeGenOptions.h
@@ -107,6 +107,20 @@
   /// Enable additional debugging information.
   std::string DebugPass;
 
+  /// Pass description string for the new pass manager.
+  /// This is primarily for experimentation while bringing up the new pass
+  /// manager. It will completely replace the middle-end pipeline and so
+  /// will interact with options that require modifying the optimization
+  /// pipeline (e.g. sanitizers).
+  std::string NewPMPasses;
+
+  /// Alias analysis pipeline for the new pass manager.
+  /// This is primarily for experimentation while bringing up the new pass
+  /// manager. It will completely replace the middle-end pipeline and so
+  /// will interact with options that require modifying the optimization
+  /// pipeline (e.g. sanitizers).
+  std::string NewPMAAPipeline;
+
   /// The string to embed in debug information as the current working directory.
   std::string DebugCompilationDir;
 
Index: lib/CodeGen/BackendUtil.cpp
===================================================================
--- lib/CodeGen/BackendUtil.cpp
+++ lib/CodeGen/BackendUtil.cpp
@@ -31,6 +31,7 @@
 #include "llvm/IR/Verifier.h"
 #include "llvm/MC/SubtargetFeature.h"
 #include "llvm/Object/ModuleSummaryIndexObjectFile.h"
+#include "llvm/Passes/PassBuilder.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/TargetRegistry.h"
@@ -315,6 +316,11 @@
   if (CodeGenOpts.DisableLLVMPasses)
     return;
 
+  // If we are going to parse a new PM pass pipeline, don't add any old PM
+  // passes here.
+  if (!CodeGenOpts.NewPMPasses.empty())
+    return;
+
   unsigned OptLevel = CodeGenOpts.OptimizationLevel;
   CodeGenOptions::InliningMethod Inlining = CodeGenOpts.getInlining();
 
@@ -744,6 +750,49 @@
   // Before executing passes, print the final values of the LLVM options.
   cl::PrintOptionValues();
 
+  if (!CodeGenOpts.NewPMPasses.empty()) {
+    // Use the new PM for the middle end.
+    // Note that we still run the old PM manager later because they contain
+    // e.g. the passes for printing out a BC or LL file (e.g. for -flto).
+    // But there is nothing else run except for the printing passes so this
+    // doesn't affect the actual optimization.
+
+    // This is a really low-level internal developer option.
+    // Use report_fatal_error if anything goes wrong.
+
+    PassBuilder PB(TM.get());
+    AAManager AA;
+    if (!PB.parseAAPipeline(AA, CodeGenOpts.NewPMAAPipeline))
+      report_fatal_error("Unable to parse AA pipeline description: " +
+                         CodeGenOpts.NewPMAAPipeline);
+
+    LoopAnalysisManager LAM;
+    FunctionAnalysisManager FAM;
+    CGSCCAnalysisManager CGAM;
+    ModuleAnalysisManager MAM;
+
+    // Register the AA manager first so that our version is the one used.
+    FAM.registerPass([&] { return std::move(AA); });
+
+    // Register all the basic analyses with the managers.
+    PB.registerModuleAnalyses(MAM);
+    PB.registerCGSCCAnalyses(CGAM);
+    PB.registerFunctionAnalyses(FAM);
+    PB.registerLoopAnalyses(LAM);
+    PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
+
+    ModulePassManager MPM;
+    MPM.addPass(VerifierPass());
+
+    // Now, add all the passes we've been requested to.
+    if (!PB.parsePassPipeline(MPM, CodeGenOpts.NewPMPasses))
+      report_fatal_error("unable to parse pass pipeline description: " +
+                         CodeGenOpts.NewPMPasses);
+
+    MPM.addPass(VerifierPass());
+    MPM.run(*TheModule, MAM);
+  }
+
   // Run passes. For now we do all passes at once, but eventually we
   // would like to have the option of streaming code generation.
 
Index: lib/CodeGen/CMakeLists.txt
===================================================================
--- lib/CodeGen/CMakeLists.txt
+++ lib/CodeGen/CMakeLists.txt
@@ -12,6 +12,7 @@
   MC
   ObjCARCOpts
   Object
+  Passes
   ProfileData
   ScalarOpts
   Support
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -840,6 +840,11 @@
   Opts.EmitCheckPathComponentsToStrip = getLastArgIntValue(
       Args, OPT_fsanitize_undefined_strip_path_components_EQ, 0, Diags);
 
+  if (Arg *A = Args.getLastArg(OPT_newpm_passes_EQ))
+    Opts.NewPMPasses = A->getValue();
+  if (Arg *A = Args.getLastArg(OPT_newpm_aa_pipeline_EQ))
+    Opts.NewPMAAPipeline = A->getValue();
+
   return Success;
 }
 
Index: test/CodeGen/newpm-passes.c
===================================================================
--- /dev/null
+++ test/CodeGen/newpm-passes.c
@@ -0,0 +1,26 @@
+// Check that passes get run.
+
+// RUN: %clang_cc1 %s -emit-llvm -o /dev/null -newpm-passes=mem2reg,aa-eval 2>&1 | FileCheck %s --check-prefix=NO-AA
+
+// NO-AA: ===== Alias Analysis Evaluator Report =====
+// NO-AA: 0 must alias responses
+
+// RUN: %clang_cc1 %s -emit-llvm -o /dev/null -newpm-passes=mem2reg,aa-eval -newpm-aa-pipeline=basic-aa 2>&1 | FileCheck %s --check-prefix=WITH-AA
+
+// WITH-AA: ===== Alias Analysis Evaluator Report =====
+// WITH-AA: 1 must alias responses
+
+
+// The actual output with -flto or -emit-llvm is generated by running a
+// pass in the old PM. Verify that that we still get output.
+
+// RUN: %clang -flto -c %s -o - -Xclang -newpm-passes=mem2reg 2>&1 | opt -S | FileCheck %s --check-prefix=OUTPUT-IS-GENERATED
+// RUN: %clang -emit-llvm -S %s -o - -Xclang -newpm-passes=mem2reg 2>&1 | FileCheck %s --check-prefix=OUTPUT-IS-GENERATED
+
+// OUTPUT-IS-GENERATED: @foo
+
+int foo(int *x) {
+  int *y = x + 1;
+  int *z = y - 1;
+  return *x + *z;
+}