Index: llvm/trunk/include/llvm/Passes/PassBuilder.h
===================================================================
--- llvm/trunk/include/llvm/Passes/PassBuilder.h
+++ llvm/trunk/include/llvm/Passes/PassBuilder.h
@@ -501,6 +501,18 @@
     PipelineStartEPCallbacks.push_back(C);
   }
 
+  /// Register a callback for a default optimizer pipeline extension point
+  ///
+  /// This extension point allows adding optimizations at the very end of the
+  /// function optimization pipeline. A key difference between this and the
+  /// legacy PassManager's OptimizerLast callback is that this extension point
+  /// is not triggered at O0. Extensions to the O0 pipeline should append their
+  /// passes to the end of the overall pipeline.
+  void registerOptimizerLastEPCallback(
+      const std::function<void(FunctionPassManager &, OptimizationLevel)> &C) {
+    OptimizerLastEPCallbacks.push_back(C);
+  }
+
   /// Register a callback for parsing an AliasAnalysis Name to populate
   /// the given AAManager \p AA
   void registerParseAACallback(
@@ -614,6 +626,8 @@
       CGSCCOptimizerLateEPCallbacks;
   SmallVector<std::function<void(FunctionPassManager &, OptimizationLevel)>, 2>
       VectorizerStartEPCallbacks;
+  SmallVector<std::function<void(FunctionPassManager &, OptimizationLevel)>, 2>
+      OptimizerLastEPCallbacks;
   // Module callbacks
   SmallVector<std::function<void(ModulePassManager &)>, 2>
       PipelineStartEPCallbacks;
Index: llvm/trunk/lib/Passes/PassBuilder.cpp
===================================================================
--- llvm/trunk/lib/Passes/PassBuilder.cpp
+++ llvm/trunk/lib/Passes/PassBuilder.cpp
@@ -862,6 +862,9 @@
   // inserting redudnancies into the progrem. This even includes SimplifyCFG.
   OptimizePM.addPass(SpeculateAroundPHIsPass());
 
+  for (auto &C : OptimizerLastEPCallbacks)
+    C(OptimizePM, Level);
+
   // Add the core optimizing pipeline.
   MPM.addPass(createModuleToFunctionPassAdaptor(std::move(OptimizePM)));
 
Index: llvm/trunk/test/Other/new-pm-defaults.ll
===================================================================
--- llvm/trunk/test/Other/new-pm-defaults.ll
+++ llvm/trunk/test/Other/new-pm-defaults.ll
@@ -66,6 +66,11 @@
 ; RUN:     -passes='lto-pre-link<O3>' -S  %s 2>&1 \
 ; RUN:     | FileCheck %s --check-prefix=CHECK-O --check-prefix=CHECK-O3 \
 ; RUN:     --check-prefix=CHECK-EP-PIPELINE-START
+; RUN: opt -disable-verify -debug-pass-manager \
+; RUN:     -passes-ep-optimizer-last='no-op-function' \
+; RUN:     -passes='default<O3>' -S  %s 2>&1 \
+; RUN:     | FileCheck %s --check-prefix=CHECK-O --check-prefix=CHECK-O3 \
+; RUN:     --check-prefix=CHECK-EP-OPTIMIZER-LAST
 
 ; CHECK-O: Running analysis: PassInstrumentationAnalysis
 ; CHECK-O-NEXT: Starting llvm::Module pass manager run.
@@ -254,6 +259,7 @@
 ; CHECK-O-NEXT: Running pass: DivRemPairsPass
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: SpeculateAroundPHIsPass
+; CHECK-EP-OPTIMIZER-LAST: Running pass: NoOpFunctionPass
 ; CHECK-O-NEXT: Finished llvm::Function pass manager run.
 ; CHECK-O-NEXT: Running pass: CGProfilePass
 ; CHECK-O-NEXT: Running pass: GlobalDCEPass
Index: llvm/trunk/tools/opt/NewPMDriver.cpp
===================================================================
--- llvm/trunk/tools/opt/NewPMDriver.cpp
+++ llvm/trunk/tools/opt/NewPMDriver.cpp
@@ -95,6 +95,12 @@
     cl::desc("A textual description of the function pass pipeline inserted at "
              "the PipelineStart extension point into default pipelines"),
     cl::Hidden);
+static cl::opt<std::string> OptimizerLastEPPipeline(
+    "passes-ep-optimizer-last",
+    cl::desc("A textual description of the function pass pipeline inserted at "
+             "the OptimizerLast extension point into default pipelines"),
+    cl::Hidden);
+
 enum PGOKind { NoPGO, InstrGen, InstrUse, SampleUse };
 static cl::opt<PGOKind> PGOKindFlag(
     "pgo-kind", cl::init(NoPGO), cl::Hidden,
@@ -195,6 +201,13 @@
           Err(PB.parsePassPipeline(PM, PipelineStartEPPipeline, VerifyEachPass,
                                    DebugLogging));
         });
+  if (tryParsePipelineText<FunctionPassManager>(PB, OptimizerLastEPPipeline))
+    PB.registerOptimizerLastEPCallback(
+        [&PB, VerifyEachPass, DebugLogging](FunctionPassManager &PM,
+                                            PassBuilder::OptimizationLevel) {
+          PB.parsePassPipeline(PM, OptimizerLastEPPipeline, VerifyEachPass,
+                               DebugLogging);
+        });
 }
 
 #ifdef LINK_POLLY_INTO_TOOLS