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| 1 | +//===- LastRunTrackingAnalysis.h - Avoid running redundant pass -*- C++ -*-===// |
| 2 | +// |
| 3 | +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | +// See https://llvm.org/LICENSE.txt for license information. |
| 5 | +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | +// |
| 7 | +//===----------------------------------------------------------------------===// |
| 8 | +// |
| 9 | +// This is an analysis pass to track a set of passes that have been run, so that |
| 10 | +// we can avoid running a pass again if there is no change since the last run of |
| 11 | +// the pass. |
| 12 | +// |
| 13 | +// In this analysis we track a set of passes S for each function with the |
| 14 | +// following transition rules: |
| 15 | +// 1. If pass P makes changes, set S = {P}. |
| 16 | +// 2. If pass P doesn't make changes, set S = S + {P}. |
| 17 | +// |
| 18 | +// Before running a pass P which satisfies P(P(x)) == P(x), we check if P is in |
| 19 | +// S. If so, we skip this pass since we know that there will be no change. |
| 20 | +// |
| 21 | +// Notes: |
| 22 | +// 1. Some transform passes have parameters that may vary in the optimization |
| 23 | +// pipeline. We should check if parameters in current run is compatible with |
| 24 | +// that in the last run. |
| 25 | +// 2. This pass only tracks at the module/function level. Loop passes are not |
| 26 | +// supported for now. |
| 27 | +// |
| 28 | +//===----------------------------------------------------------------------===// |
| 29 | + |
| 30 | +#ifndef LLVM_ANALYSIS_LASTRUNTRACKINGANALYSIS_H |
| 31 | +#define LLVM_ANALYSIS_LASTRUNTRACKINGANALYSIS_H |
| 32 | + |
| 33 | +#include "llvm/ADT/DenseMap.h" |
| 34 | +#include "llvm/IR/PassManager.h" |
| 35 | +#include <functional> |
| 36 | + |
| 37 | +namespace llvm { |
| 38 | + |
| 39 | +/// This class is used to track the last run of a set of module/function passes. |
| 40 | +/// Invalidation are conservatively handled by the pass manager if a pass |
| 41 | +/// doesn't explicitly preserve the result. |
| 42 | +/// If we want to skip a pass, we should define a unique ID \p PassID to |
| 43 | +/// identify the pass, which is usually a pointer to a static member. If a pass |
| 44 | +/// has parameters, they should be stored in a struct \p OptionT with a method |
| 45 | +/// bool isCompatibleWith(const OptionT& LastOpt) const to check compatibility. |
| 46 | +class LastRunTrackingInfo { |
| 47 | +public: |
| 48 | + using PassID = const void *; |
| 49 | + using OptionPtr = const void *; |
| 50 | + // CompatibilityCheckFn is a closure that stores the parameters of last run. |
| 51 | + using CompatibilityCheckFn = std::function<bool(OptionPtr)>; |
| 52 | + |
| 53 | + /// Check if we should skip a pass. |
| 54 | + /// \param ID The unique ID of the pass. |
| 55 | + /// \param Opt The parameters of the pass. If the pass has no parameters, use |
| 56 | + /// shouldSkip(PassID ID) instead. |
| 57 | + /// \return True if we should skip the pass. |
| 58 | + /// \sa shouldSkip(PassID ID) |
| 59 | + template <typename OptionT> |
| 60 | + bool shouldSkip(PassID ID, const OptionT &Opt) const { |
| 61 | + return shouldSkipImpl(ID, &Opt); |
| 62 | + } |
| 63 | + bool shouldSkip(PassID ID) const { return shouldSkipImpl(ID, nullptr); } |
| 64 | + |
| 65 | + /// Update the tracking info. |
| 66 | + /// \param ID The unique ID of the pass. |
| 67 | + /// \param Changed Whether the pass makes changes. |
| 68 | + /// \param Opt The parameters of the pass. It must have the same type as the |
| 69 | + /// parameters of the last run. If the pass has no parameters, use |
| 70 | + /// update(PassID ID, bool Changed) instead. |
| 71 | + /// \sa update(PassID ID, bool Changed) |
| 72 | + template <typename OptionT> |
| 73 | + void update(PassID ID, bool Changed, const OptionT &Opt) { |
| 74 | + updateImpl(ID, Changed, [Opt](OptionPtr Ptr) { |
| 75 | + return static_cast<const OptionT *>(Ptr)->isCompatibleWith(Opt); |
| 76 | + }); |
| 77 | + } |
| 78 | + void update(PassID ID, bool Changed) { |
| 79 | + updateImpl(ID, Changed, CompatibilityCheckFn{}); |
| 80 | + } |
| 81 | + |
| 82 | +private: |
| 83 | + bool shouldSkipImpl(PassID ID, OptionPtr Ptr) const; |
| 84 | + void updateImpl(PassID ID, bool Changed, CompatibilityCheckFn CheckFn); |
| 85 | + |
| 86 | + DenseMap<PassID, CompatibilityCheckFn> TrackedPasses; |
| 87 | +}; |
| 88 | + |
| 89 | +/// A function/module analysis which provides an empty \c LastRunTrackingInfo. |
| 90 | +class LastRunTrackingAnalysis final |
| 91 | + : public AnalysisInfoMixin<LastRunTrackingAnalysis> { |
| 92 | + friend AnalysisInfoMixin<LastRunTrackingAnalysis>; |
| 93 | + static AnalysisKey Key; |
| 94 | + |
| 95 | +public: |
| 96 | + using Result = LastRunTrackingInfo; |
| 97 | + LastRunTrackingInfo run(Function &F, FunctionAnalysisManager &) { |
| 98 | + return LastRunTrackingInfo(); |
| 99 | + } |
| 100 | + LastRunTrackingInfo run(Module &M, ModuleAnalysisManager &) { |
| 101 | + return LastRunTrackingInfo(); |
| 102 | + } |
| 103 | +}; |
| 104 | + |
| 105 | +} // namespace llvm |
| 106 | + |
| 107 | +#endif // LLVM_ANALYSIS_LASTRUNTRACKINGANALYSIS_H |
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