Index: include/llvm/LTO/Config.h
===================================================================
--- include/llvm/LTO/Config.h
+++ include/llvm/LTO/Config.h
@@ -78,6 +78,11 @@
   /// Disable entirely the optimizer, including importing for ThinLTO
   bool CodeGenOnly = false;
 
+  /// If this field is set, the set of passes run in the middle-end optimizer
+  /// will be the one specified by the string. Only works with the new pass
+  /// manager as the old one doesn't have this ability.
+  std::string OptPipeline;
+
   /// Setting this field will replace target triples in input files with this
   /// triple.
   std::string OverrideTriple;
@@ -164,6 +169,7 @@
         RelocModel(std::move(X.RelocModel)), CodeModel(std::move(X.CodeModel)),
         CGOptLevel(std::move(X.CGOptLevel)), OptLevel(std::move(X.OptLevel)),
         DisableVerify(std::move(X.DisableVerify)),
+        OptPipeline(std::move(X.OptPipeline)),
         OverrideTriple(std::move(X.OverrideTriple)),
         DefaultTriple(std::move(X.DefaultTriple)),
         ShouldDiscardValueNames(std::move(X.ShouldDiscardValueNames)),
@@ -187,6 +193,7 @@
     CGOptLevel = std::move(X.CGOptLevel);
     OptLevel = std::move(X.OptLevel);
     DisableVerify = std::move(X.DisableVerify);
+    OptPipeline = std::move(X.OptPipeline);
     OverrideTriple = std::move(X.OverrideTriple);
     DefaultTriple = std::move(X.DefaultTriple);
     ShouldDiscardValueNames = std::move(X.ShouldDiscardValueNames);
Index: lib/LTO/LLVMBuild.txt
===================================================================
--- lib/LTO/LLVMBuild.txt
+++ lib/LTO/LLVMBuild.txt
@@ -31,6 +31,7 @@
  MC
  ObjCARC
  Object
+ Passes
  Scalar
  Support
  Target
Index: lib/LTO/LTOBackend.cpp
===================================================================
--- lib/LTO/LTOBackend.cpp
+++ lib/LTO/LTOBackend.cpp
@@ -15,12 +15,18 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/LTO/LTOBackend.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/CGSCCPassManager.h"
+#include "llvm/Analysis/LoopPassManager.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Bitcode/ReaderWriter.h"
 #include "llvm/IR/LegacyPassManager.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/IR/Verifier.h"
 #include "llvm/LTO/LTO.h"
 #include "llvm/MC/SubtargetFeature.h"
+#include "llvm/Passes/PassBuilder.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/TargetRegistry.h"
@@ -114,6 +120,41 @@
       C.CodeModel, C.CGOptLevel));
 }
 
+static void runNewPMCustomPasses(Module &M, TargetMachine *TM,
+                                 std::string PipelineDesc,
+                                 bool DisableVerify) {
+  PassBuilder PB(TM);
+  AAManager AA;
+  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;
+
+  // Always verify the input.
+  MPM.addPass(VerifierPass());
+
+  // Now, add all the passes we've been requested to.
+  if (!PB.parsePassPipeline(MPM, PipelineDesc))
+    report_fatal_error("unable to parse pass pipeline description: " +
+                       PipelineDesc);
+
+  if (!DisableVerify)
+    MPM.addPass(VerifierPass());
+  MPM.run(M, MAM);
+}
+
 static void runOldPMPasses(Config &C, Module &M, TargetMachine *TM,
                            bool IsThinLto) {
   legacy::PassManager passes;
@@ -139,7 +180,10 @@
 bool opt(Config &C, TargetMachine *TM, unsigned Task, Module &M,
          bool IsThinLto) {
   M.setDataLayout(TM->createDataLayout());
-  runOldPMPasses(C, M, TM, IsThinLto);
+  if (C.OptPipeline.empty())
+    runOldPMPasses(C, M, TM, IsThinLto);
+  else
+    runNewPMCustomPasses(M, TM, C.OptPipeline, C.DisableVerify);
   return !C.PostOptModuleHook || C.PostOptModuleHook(Task, M);
 }
 
Index: test/tools/llvm-lto2/X86/pipeline.ll
===================================================================
--- /dev/null
+++ test/tools/llvm-lto2/X86/pipeline.ll
@@ -0,0 +1,24 @@
+; RUN: llvm-as < %s > %t1.bc
+
+; Try a custom pipeline
+; RUN: llvm-lto2 %t1.bc -o %t.o -save-temps \
+; RUN:  -r %t1.bc,patatino,px -opt-pipeline loweratomic
+; RUN: llvm-dis < %t.o.0.4.opt.bc | FileCheck %s --check-prefix=CUSTOM
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @patatino() {
+  fence seq_cst
+  ret void
+}
+
+; CUSTOM: define void @patatino() {
+; CUSTOM-NEXT:   ret void
+; CUSTOM-NEXT: }
+
+; Check that invalid pipeline are caught as errors.
+; RUN: not llvm-lto2 %t1.bc -o %t.o -save-temps \
+; RUN:  -r %t1.bc,patatino,px -opt-pipeline foogoo 2>&1 | \
+; RUN:  FileCheck %s --check-prefix=ERR
+
+; ERR: LLVM ERROR: unable to parse pass pipeline description: foogoo
Index: tools/llvm-lto2/llvm-lto2.cpp
===================================================================
--- tools/llvm-lto2/llvm-lto2.cpp
+++ tools/llvm-lto2/llvm-lto2.cpp
@@ -35,6 +35,10 @@
 static cl::opt<std::string> CacheDir("cache-dir", cl::desc("Cache Directory"),
                                      cl::value_desc("directory"));
 
+static cl::opt<std::string> OptPipeline("opt-pipeline",
+                                        cl::desc("Optimizer Pipeline"),
+                                        cl::value_desc("pipeline"));
+
 static cl::opt<bool> SaveTemps("save-temps", cl::desc("Save temporary files"));
 
 static cl::opt<bool>
@@ -148,6 +152,9 @@
     check(Conf.addSaveTemps(OutputFilename + "."),
           "Config::addSaveTemps failed");
 
+  // Run a custom pipeline, if asked for.
+  Conf.OptPipeline = OptPipeline;
+
   ThinBackend Backend;
   if (ThinLTODistributedIndexes)
     Backend = createWriteIndexesThinBackend("", "", true, "");