Add an OptimizerLast EP

Summary:
It turns out that we need an OptimizerLast PassBuilder extension point
after all. I missed the relevance of this EP the first time. By legacy PM magic,
function passes added at this EP get added to the last _Function_ PM, which is a
feature we lost when dropping this EP for the new PM.

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.

Differential Revision: https://reviews.llvm.org/D54374

llvm-svn: 346645

llvm/include/llvm/Passes/PassBuilder.h

@@ -501,6 +501,18 @@ class PassBuilder {
     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 @@ class PassBuilder {
       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;

llvm/lib/Passes/PassBuilder.cpp

@@ -862,6 +862,9 @@ PassBuilder::buildModuleOptimizationPipeline(OptimizationLevel Level,
   // 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)));
 

llvm/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

llvm/tools/opt/NewPMDriver.cpp

@@ -95,6 +95,12 @@ static cl::opt<std::string> PipelineStartEPPipeline(
     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 @@ static void registerEPCallbacks(PassBuilder &PB, bool VerifyEachPass,
           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