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 MachineFunction &MF; 48 LiveIntervals &LIS; 49 const VirtRegMap &VRM; 50 const MachineLoopInfo &Loops; 51 const MachineBlockFrequencyInfo &MBFI; 52 53 /// Returns true if Reg of live interval LI is used in instruction with many 54 /// operands like STATEPOINT. 55 bool isLiveAtStatepointVarArg(LiveInterval &LI); 56 57 public: 58 VirtRegAuxInfo(MachineFunction &MF, LiveIntervals &LIS, 59 const VirtRegMap &VRM, const MachineLoopInfo &Loops, 60 const MachineBlockFrequencyInfo &MBFI) 61 : MF(MF), LIS(LIS), VRM(VRM), Loops(Loops), MBFI(MBFI) {} 62 63 virtual ~VirtRegAuxInfo() = default; 64 65 /// (re)compute li's spill weight and allocation hint. 66 void calculateSpillWeightAndHint(LiveInterval &LI); 67 68 /// Compute future expected spill weight of a split artifact of LI 69 /// that will span between start and end slot indexes. 70 /// \param LI The live interval to be split. 71 /// \param Start The expected beginning of the split artifact. Instructions 72 /// before start will not affect the weight. 73 /// \param End The expected end of the split artifact. Instructions 74 /// after end will not affect the weight. 75 /// \return The expected spill weight of the split artifact. Returns 76 /// negative weight for unspillable LI. 77 float futureWeight(LiveInterval &LI, SlotIndex Start, SlotIndex End); 78 79 /// Compute spill weights and allocation hints for all virtual register 80 /// live intervals. 81 void calculateSpillWeightsAndHints(); 82 83 protected: 84 /// Helper function for weight calculations. 85 /// (Re)compute LI's spill weight and allocation hint, or, for non null 86 /// start and end - compute future expected spill weight of a split 87 /// artifact of LI that will span between start and end slot indexes. 88 /// \param LI The live interval for which to compute the weight. 89 /// \param Start The expected beginning of the split artifact. Instructions 90 /// before start will not affect the weight. Relevant for 91 /// weight calculation of future split artifact. 92 /// \param End The expected end of the split artifact. Instructions 93 /// after end will not affect the weight. Relevant for 94 /// weight calculation of future split artifact. 95 /// \return The spill weight. Returns negative weight for unspillable LI. 96 float weightCalcHelper(LiveInterval &LI, SlotIndex *Start = nullptr, 97 SlotIndex *End = nullptr); 98 99 /// Weight normalization function. 100 virtual float normalize(float UseDefFreq, unsigned Size, 101 unsigned NumInstr) { 102 return normalizeSpillWeight(UseDefFreq, Size, NumInstr); 103 } 104 }; 105 } // end namespace llvm 106 107 #endif // LLVM_CODEGEN_CALCSPILLWEIGHTS_H 108