[Analysis] Avoid running transform passes that have just been run (#1…

…12092)

This patch adds a new analysis pass to track a set of passes and their
parameters to see if we can avoid running transform passes that have
just been run. The current implementation only skips redundant
InstCombine runs. I will add support for other passes in follow-up
patches.

RFC link:
https://discourse.llvm.org/t/rfc-pipeline-avoid-running-transform-passes-that-have-just-been-run/82467

Compile time improvement:
http://llvm-compile-time-tracker.com/compare.php?from=76007138f4ffd4e0f510d12b5e8cad529c21f24d&to=64134cf07ea7eb39c60320087c0c5afdc16c3a2b&stat=instructions%3Au

llvm/include/llvm/Analysis/LastRunTrackingAnalysis.h

@@ -0,0 +1,107 @@
+//===- LastRunTrackingAnalysis.h - Avoid running redundant pass -*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This is an analysis pass to track a set of passes that have been run, so that
+// we can avoid running a pass again if there is no change since the last run of
+// the pass.
+//
+// In this analysis we track a set of passes S for each function with the
+// following transition rules:
+//   1. If pass P makes changes, set S = {P}.
+//   2. If pass P doesn't make changes, set S = S + {P}.
+//
+// Before running a pass P which satisfies P(P(x)) == P(x), we check if P is in
+// S. If so, we skip this pass since we know that there will be no change.
+//
+// Notes:
+//   1. Some transform passes have parameters that may vary in the optimization
+//   pipeline. We should check if parameters in current run is compatible with
+//   that in the last run.
+//   2. This pass only tracks at the module/function level. Loop passes are not
+//   supported for now.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_LASTRUNTRACKINGANALYSIS_H
+#define LLVM_ANALYSIS_LASTRUNTRACKINGANALYSIS_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/IR/PassManager.h"
+#include <functional>
+
+namespace llvm {
+
+/// This class is used to track the last run of a set of module/function passes.
+/// Invalidation are conservatively handled by the pass manager if a pass
+/// doesn't explicitly preserve the result.
+/// If we want to skip a pass, we should define a unique ID \p PassID to
+/// identify the pass, which is usually a pointer to a static member. If a pass
+/// has parameters, they should be stored in a struct \p OptionT with a method
+/// bool isCompatibleWith(const OptionT& LastOpt) const to check compatibility.
+class LastRunTrackingInfo {
+public:
+  using PassID = const void *;
+  using OptionPtr = const void *;
+  // CompatibilityCheckFn is a closure that stores the parameters of last run.
+  using CompatibilityCheckFn = std::function<bool(OptionPtr)>;
+
+  /// Check if we should skip a pass.
+  /// \param ID The unique ID of the pass.
+  /// \param Opt The parameters of the pass. If the pass has no parameters, use
+  /// shouldSkip(PassID ID) instead.
+  /// \return True if we should skip the pass.
+  /// \sa shouldSkip(PassID ID)
+  template <typename OptionT>
+  bool shouldSkip(PassID ID, const OptionT &Opt) const {
+    return shouldSkipImpl(ID, &Opt);
+  }
+  bool shouldSkip(PassID ID) const { return shouldSkipImpl(ID, nullptr); }
+
+  /// Update the tracking info.
+  /// \param ID The unique ID of the pass.
+  /// \param Changed Whether the pass makes changes.
+  /// \param Opt The parameters of the pass. It must have the same type as the
+  /// parameters of the last run. If the pass has no parameters, use
+  /// update(PassID ID, bool Changed) instead.
+  /// \sa update(PassID ID, bool Changed)
+  template <typename OptionT>
+  void update(PassID ID, bool Changed, const OptionT &Opt) {
+    updateImpl(ID, Changed, [Opt](OptionPtr Ptr) {
+      return static_cast<const OptionT *>(Ptr)->isCompatibleWith(Opt);
+    });
+  }
+  void update(PassID ID, bool Changed) {
+    updateImpl(ID, Changed, CompatibilityCheckFn{});
+  }
+
+private:
+  bool shouldSkipImpl(PassID ID, OptionPtr Ptr) const;
+  void updateImpl(PassID ID, bool Changed, CompatibilityCheckFn CheckFn);
+
+  DenseMap<PassID, CompatibilityCheckFn> TrackedPasses;
+};
+
+/// A function/module analysis which provides an empty \c LastRunTrackingInfo.
+class LastRunTrackingAnalysis final
+    : public AnalysisInfoMixin<LastRunTrackingAnalysis> {
+  friend AnalysisInfoMixin<LastRunTrackingAnalysis>;
+  static AnalysisKey Key;
+
+public:
+  using Result = LastRunTrackingInfo;
+  LastRunTrackingInfo run(Function &F, FunctionAnalysisManager &) {
+    return LastRunTrackingInfo();
+  }
+  LastRunTrackingInfo run(Module &M, ModuleAnalysisManager &) {
+    return LastRunTrackingInfo();
+  }
+};
+
+} // namespace llvm
+
+#endif // LLVM_ANALYSIS_LASTRUNTRACKINGANALYSIS_H

llvm/include/llvm/Transforms/InstCombine/InstCombine.h

@@ -49,6 +49,7 @@ class InstCombinePass : public PassInfoMixin<InstCombinePass> {
 private:
   InstructionWorklist Worklist;
   InstCombineOptions Options;
+  static char ID;
 
 public:
   explicit InstCombinePass(InstCombineOptions Opts = {});

llvm/lib/Analysis/CMakeLists.txt

@@ -79,6 +79,7 @@ add_llvm_component_library(LLVMAnalysis
   InstructionPrecedenceTracking.cpp
   InstructionSimplify.cpp
   InteractiveModelRunner.cpp
+  LastRunTrackingAnalysis.cpp
   LazyBranchProbabilityInfo.cpp
   LazyBlockFrequencyInfo.cpp
   LazyCallGraph.cpp

llvm/lib/Analysis/LastRunTrackingAnalysis.cpp

@@ -0,0 +1,51 @@
+//===- LastRunTrackingAnalysis.cpp - Avoid running redundant pass -*- C++ -*-=//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This is an analysis pass to track a set of passes that have been run, so that
+// we can avoid running a pass again if there is no change since the last run of
+// the pass.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/LastRunTrackingAnalysis.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/CommandLine.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "last-run-tracking"
+STATISTIC(NumSkippedPasses, "Number of skipped passes");
+STATISTIC(NumLRTQueries, "Number of LastRunTracking queries");
+
+static cl::opt<bool>
+    DisableLastRunTracking("disable-last-run-tracking", cl::Hidden,
+                           cl::desc("Disable last run tracking"),
+                           cl::init(false));
+
+bool LastRunTrackingInfo::shouldSkipImpl(PassID ID, OptionPtr Ptr) const {
+  if (DisableLastRunTracking)
+    return false;
+  ++NumLRTQueries;
+  auto Iter = TrackedPasses.find(ID);
+  if (Iter == TrackedPasses.end())
+    return false;
+  if (!Iter->second || Iter->second(Ptr)) {
+    ++NumSkippedPasses;
+    return true;
+  }
+  return false;
+}
+
+void LastRunTrackingInfo::updateImpl(PassID ID, bool Changed,
+                                     CompatibilityCheckFn CheckFn) {
+  if (Changed)
+    TrackedPasses.clear();
+  TrackedPasses[ID] = std::move(CheckFn);
+}
+
+AnalysisKey LastRunTrackingAnalysis::Key;

llvm/lib/Passes/PassBuilder.cpp

@@ -46,6 +46,7 @@
 #include "llvm/Analysis/InlineAdvisor.h"
 #include "llvm/Analysis/InlineSizeEstimatorAnalysis.h"
 #include "llvm/Analysis/InstCount.h"
+#include "llvm/Analysis/LastRunTrackingAnalysis.h"
 #include "llvm/Analysis/LazyCallGraph.h"
 #include "llvm/Analysis/LazyValueInfo.h"
 #include "llvm/Analysis/Lint.h"

llvm/lib/Passes/PassRegistry.def

@@ -25,6 +25,7 @@ MODULE_ANALYSIS("dxil-metadata", DXILMetadataAnalysis())
 MODULE_ANALYSIS("dxil-resource", DXILResourceAnalysis())
 MODULE_ANALYSIS("inline-advisor", InlineAdvisorAnalysis())
 MODULE_ANALYSIS("ir-similarity", IRSimilarityAnalysis())
+MODULE_ANALYSIS("last-run-tracking", LastRunTrackingAnalysis())
 MODULE_ANALYSIS("lcg", LazyCallGraphAnalysis())
 MODULE_ANALYSIS("module-summary", ModuleSummaryIndexAnalysis())
 MODULE_ANALYSIS("no-op-module", NoOpModuleAnalysis())
@@ -286,6 +287,7 @@ FUNCTION_ANALYSIS(
     MachineFunctionAnalysis(static_cast<const LLVMTargetMachine *>(TM)))
 FUNCTION_ANALYSIS("gc-function", GCFunctionAnalysis())
 FUNCTION_ANALYSIS("inliner-size-estimator", InlineSizeEstimatorAnalysis())
+FUNCTION_ANALYSIS("last-run-tracking", LastRunTrackingAnalysis())
 FUNCTION_ANALYSIS("lazy-value-info", LazyValueAnalysis())
 FUNCTION_ANALYSIS("loops", LoopAnalysis())
 FUNCTION_ANALYSIS("memdep", MemoryDependenceAnalysis())

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -47,6 +47,7 @@
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/LastRunTrackingAnalysis.h"
 #include "llvm/Analysis/LazyBlockFrequencyInfo.h"
 #include "llvm/Analysis/MemoryBuiltins.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
@@ -5545,8 +5546,15 @@ void InstCombinePass::printPipeline(
   OS << '>';
 }
 
+char InstCombinePass::ID = 0;
+
 PreservedAnalyses InstCombinePass::run(Function &F,
                                        FunctionAnalysisManager &AM) {
+  auto &LRT = AM.getResult<LastRunTrackingAnalysis>(F);
+  // No changes since last InstCombine pass, exit early.
+  if (LRT.shouldSkip(&ID))
+    return PreservedAnalyses::all();
+
   auto &AC = AM.getResult<AssumptionAnalysis>(F);
   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
   auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
@@ -5562,12 +5570,16 @@ PreservedAnalyses InstCombinePass::run(Function &F,
   auto *BPI = AM.getCachedResult<BranchProbabilityAnalysis>(F);
 
   if (!combineInstructionsOverFunction(F, Worklist, AA, AC, TLI, TTI, DT, ORE,
-                                       BFI, BPI, PSI, Options))
+                                       BFI, BPI, PSI, Options)) {
     // No changes, all analyses are preserved.
+    LRT.update(&ID, /*Changed=*/false);
     return PreservedAnalyses::all();
+  }
 
   // Mark all the analyses that instcombine updates as preserved.
   PreservedAnalyses PA;
+  LRT.update(&ID, /*Changed=*/true);
+  PA.preserve<LastRunTrackingAnalysis>();
   PA.preserveSet<CFGAnalyses>();
   return PA;
 }

llvm/test/Other/new-pm-defaults.ll

@@ -118,6 +118,7 @@
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running pass: PromotePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
+; CHECK-O-NEXT: Running analysis: LastRunTrackingAnalysis
 ; CHECK-O-NEXT: Running analysis: OptimizationRemarkEmitterAnalysis
 ; CHECK-O-NEXT: Running analysis: AAManager
 ; CHECK-O-NEXT: Running analysis: BasicAA

llvm/test/Other/new-pm-lto-defaults.ll

@@ -67,6 +67,7 @@
 ; CHECK-O23SZ-NEXT: Running pass: ConstantMergePass
 ; CHECK-O23SZ-NEXT: Running pass: DeadArgumentEliminationPass
 ; CHECK-O23SZ-NEXT: Running pass: InstCombinePass
+; CHECK-O23SZ-NEXT: Running analysis: LastRunTrackingAnalysis
 ; CHECK-O23SZ-NEXT: Running pass: AggressiveInstCombinePass
 ; CHECK-EP-Peephole-NEXT: Running pass: NoOpFunctionPass
 ; CHECK-O23SZ-NEXT: Running pass: ExpandVariadicsPass

llvm/test/Other/new-pm-thinlto-postlink-defaults.ll

@@ -54,6 +54,7 @@
 ; CHECK-O-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-O-NEXT: Running pass: PromotePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
+; CHECK-O-NEXT: Running analysis: LastRunTrackingAnalysis
 ; CHECK-O-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-O-NEXT: Running analysis: AAManager
 ; CHECK-O-NEXT: Running analysis: BasicAA

llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll

@@ -39,6 +39,7 @@
 ; CHECK-O-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-O-NEXT: Running pass: PromotePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
+; CHECK-O-NEXT: Running analysis: LastRunTrackingAnalysis
 ; CHECK-O-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-O-NEXT: Running analysis: AAManager
 ; CHECK-O-NEXT: Running analysis: BasicAA

llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll

@@ -48,6 +48,7 @@
 ; CHECK-O-NEXT: Running analysis: TargetLibraryAnalysis
 ; CHECK-O-NEXT: Running pass: PromotePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
+; CHECK-O-NEXT: Running analysis: LastRunTrackingAnalysis
 ; CHECK-O-NEXT: Running analysis: AAManager on foo
 ; CHECK-O-NEXT: Running analysis: BasicAA
 ; CHECK-O-NEXT: Running analysis: ScopedNoAliasAA

llvm/test/Other/new-pm-thinlto-prelink-defaults.ll

@@ -86,6 +86,7 @@
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running pass: PromotePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
+; CHECK-O-NEXT: Running analysis: LastRunTrackingAnalysis
 ; CHECK-O-NEXT: Running analysis: OptimizationRemarkEmitterAnalysis
 ; CHECK-O-NEXT: Running analysis: AAManager
 ; CHECK-O-NEXT: Running analysis: BasicAA

llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll

@@ -50,6 +50,7 @@
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running pass: PromotePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
+; CHECK-O-NEXT: Running analysis: LastRunTrackingAnalysis
 ; CHECK-O-NEXT: Running analysis: OptimizationRemarkEmitterAnalysis
 ; CHECK-O-NEXT: Running analysis: AAManager
 ; CHECK-O-NEXT: Running analysis: BasicAA
@@ -122,6 +123,7 @@
 ; CHECK-O23SZ-NEXT: Invalidating analysis: LazyValueAnalysis
 ; CHECK-O-NEXT: Running pass: SimplifyCFGPass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
+; CHECK-O-NEXT: Running analysis: LastRunTrackingAnalysis
 ; CHECK-O-NEXT: Running analysis: BlockFrequencyAnalysis on foo
 ; CHECK-O-NEXT: Running analysis: BranchProbabilityAnalysis on foo
 ; CHECK-O-NEXT: Running analysis: LoopAnalysis on foo

llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll

@@ -53,6 +53,7 @@
 ; CHECK-O-NEXT: Running pass: GlobalOptPass
 ; CHECK-O-NEXT: Running pass: PromotePass
 ; CHECK-O-NEXT: Running pass: InstCombinePass
+; CHECK-O-NEXT: Running analysis: LastRunTrackingAnalysis
 ; CHECK-O-NEXT: Running analysis: OptimizationRemarkEmitterAnalysis on foo
 ; CHECK-O-NEXT: Running analysis: AAManager on foo
 ; CHECK-O-NEXT: Running analysis: BasicAA

llvm/test/Transforms/Coroutines/coro-retcon-opaque-ptr.ll

@@ -33,9 +33,11 @@ cleanup:                                          ; preds = %loop
 define i32 @main() {
 ; CHECK-LABEL: @main(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    call void @print(i32 4)
-; CHECK-NEXT:    call void @print(i32 5), !noalias !0
-; CHECK-NEXT:    call void @print(i32 6), !noalias !3
+; CHECK-NEXT:    tail call void @print(i32 4)
+; CHECK-NEXT:    tail call void @llvm.experimental.noalias.scope.decl(metadata [[META0:![0-9]+]])
+; CHECK-NEXT:    tail call void @print(i32 5), !noalias [[META0]]
+; CHECK-NEXT:    tail call void @llvm.experimental.noalias.scope.decl(metadata [[META3:![0-9]+]])
+; CHECK-NEXT:    tail call void @print(i32 6), !noalias [[META3]]
 ; CHECK-NEXT:    ret i32 0
 ;
 entry:

llvm/test/Transforms/Coroutines/coro-retcon.ll

@@ -43,8 +43,10 @@ define i32 @main() {
 ; CHECK-LABEL: @main(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    tail call void @print(i32 4)
-; CHECK-NEXT:    tail call void @print(i32 5), !noalias !0
-; CHECK-NEXT:    tail call void @print(i32 6), !noalias !3
+; CHECK-NEXT:    tail call void @llvm.experimental.noalias.scope.decl(metadata [[META0:![0-9]+]])
+; CHECK-NEXT:    tail call void @print(i32 5), !noalias [[META0]]
+; CHECK-NEXT:    tail call void @llvm.experimental.noalias.scope.decl(metadata [[META3:![0-9]+]])
+; CHECK-NEXT:    tail call void @print(i32 6), !noalias [[META3]]
 ; CHECK-NEXT:    ret i32 0
 ;
 ; CORO-LABEL: @main(

llvm/unittests/Analysis/CMakeLists.txt

@@ -33,6 +33,7 @@ set(ANALYSIS_TEST_SOURCES
   InlineCostTest.cpp
   IRSimilarityIdentifierTest.cpp
   IVDescriptorsTest.cpp
+  LastRunTrackingAnalysisTest.cpp
   LazyCallGraphTest.cpp
   LoadsTest.cpp
   LoopInfoTest.cpp