1 //===- lib/CodeGen/CalcSpillWeights.h ---------------------------*- 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 #ifndef LLVM_CODEGEN_CALCSPILLWEIGHTS_H 10 #define LLVM_CODEGEN_CALCSPILLWEIGHTS_H 11 12 #include "llvm/ADT/DenseMap.h" 13 #include "llvm/CodeGen/SlotIndexes.h" 14 15 namespace llvm { 16 17 class LiveInterval; 18 class LiveIntervals; 19 class MachineBlockFrequencyInfo; 20 class MachineFunction; 21 class MachineLoopInfo; 22 class VirtRegMap; 23 24 /// Normalize the spill weight of a live interval 25 /// 26 /// The spill weight of a live interval is computed as: 27 /// 28 /// (sum(use freq) + sum(def freq)) / (K + size) 29 /// 30 /// @param UseDefFreq Expected number of executed use and def instructions 31 /// per function call. Derived from block frequencies. 32 /// @param Size Size of live interval as returnexd by getSize() 33 /// @param NumInstr Number of instructions using this live interval 34 static inline float normalizeSpillWeight(float UseDefFreq, unsigned Size, 35 unsigned NumInstr) { 36 // The constant 25 instructions is added to avoid depending too much on 37 // accidental SlotIndex gaps for small intervals. The effect is that small 38 // intervals have a spill weight that is mostly proportional to the number 39 // of uses, while large intervals get a spill weight that is closer to a use 40 // density. 41 return UseDefFreq / (Size + 25*SlotIndex::InstrDist); 42 } 43 44 /// Calculate auxiliary information for a virtual register such as its 45 /// spill weight and allocation hint. 46 class VirtRegAuxInfo { 47 public: 48 using NormalizingFn = float (*)(float, unsigned, unsigned); 49 50 private: 51 MachineFunction &MF; 52 LiveIntervals &LIS; 53 VirtRegMap *VRM; 54 const MachineLoopInfo &Loops; 55 const MachineBlockFrequencyInfo &MBFI; 56 DenseMap<unsigned, float> Hint; 57 NormalizingFn normalize; 58 59 public: 60 VirtRegAuxInfo(MachineFunction &mf, LiveIntervals &lis, 61 VirtRegMap *vrm, const MachineLoopInfo &loops, 62 const MachineBlockFrequencyInfo &mbfi, 63 NormalizingFn norm = normalizeSpillWeight) 64 : MF(mf), LIS(lis), VRM(vrm), Loops(loops), MBFI(mbfi), normalize(norm) {} 65 66 /// (re)compute li's spill weight and allocation hint. 67 void calculateSpillWeightAndHint(LiveInterval &li); 68 69 /// Compute future expected spill weight of a split artifact of li 70 /// that will span between start and end slot indexes. 71 /// \param li The live interval to be split. 72 /// \param start The expected begining of the split artifact. Instructions 73 /// before start will not affect the weight. 74 /// \param end The expected end of the split artifact. Instructions 75 /// after end will not affect the weight. 76 /// \return The expected spill weight of the split artifact. Returns 77 /// negative weight for unspillable li. 78 float futureWeight(LiveInterval &li, SlotIndex start, SlotIndex end); 79 80 /// Helper function for weight calculations. 81 /// (Re)compute li's spill weight and allocation hint, or, for non null 82 /// start and end - compute future expected spill weight of a split 83 /// artifact of li that will span between start and end slot indexes. 84 /// \param li The live interval for which to compute the weight. 85 /// \param start The expected begining of the split artifact. Instructions 86 /// before start will not affect the weight. Relevant for 87 /// weight calculation of future split artifact. 88 /// \param end The expected end of the split artifact. Instructions 89 /// after end will not affect the weight. Relevant for 90 /// weight calculation of future split artifact. 91 /// \return The spill weight. Returns negative weight for unspillable li. 92 float weightCalcHelper(LiveInterval &li, SlotIndex *start = nullptr, 93 SlotIndex *end = nullptr); 94 }; 95 96 /// Compute spill weights and allocation hints for all virtual register 97 /// live intervals. 98 void calculateSpillWeightsAndHints(LiveIntervals &LIS, MachineFunction &MF, 99 VirtRegMap *VRM, 100 const MachineLoopInfo &MLI, 101 const MachineBlockFrequencyInfo &MBFI, 102 VirtRegAuxInfo::NormalizingFn norm = 103 normalizeSpillWeight); 104 105 } // end namespace llvm 106 107 #endif // LLVM_CODEGEN_CALCSPILLWEIGHTS_H 108