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/CodeGen/SlotIndexes.h" 13 14 namespace llvm { 15 16 class LiveInterval; 17 class LiveIntervals; 18 class MachineBlockFrequencyInfo; 19 class MachineFunction; 20 class MachineLoopInfo; 21 class ProfileSummaryInfo; 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 ProfileSummaryInfo *PSI; 52 const MachineBlockFrequencyInfo &MBFI; 53 54 /// Returns true if Reg of live interval LI is used in instruction with many 55 /// operands like STATEPOINT. 56 bool isLiveAtStatepointVarArg(LiveInterval &LI); 57 58 public: 59 VirtRegAuxInfo(MachineFunction &MF, LiveIntervals &LIS, 60 const VirtRegMap &VRM, const MachineLoopInfo &Loops, 61 const MachineBlockFrequencyInfo &MBFI, 62 ProfileSummaryInfo *PSI = nullptr) 63 : MF(MF), LIS(LIS), VRM(VRM), Loops(Loops), PSI(PSI), MBFI(MBFI) {} 64 65 virtual ~VirtRegAuxInfo() = default; 66 67 /// (re)compute li's spill weight and allocation hint. 68 void calculateSpillWeightAndHint(LiveInterval &LI); 69 70 /// Compute spill weights and allocation hints for all virtual register 71 /// live intervals. 72 void calculateSpillWeightsAndHints(); 73 74 /// Return the preferred allocation register for reg, given a COPY 75 /// instruction. 76 static Register copyHint(const MachineInstr *MI, unsigned Reg, 77 const TargetRegisterInfo &TRI, 78 const MachineRegisterInfo &MRI); 79 80 /// Determine if all values in LI are rematerializable. 81 static bool isRematerializable(const LiveInterval &LI, 82 const LiveIntervals &LIS, 83 const VirtRegMap &VRM, 84 const TargetInstrInfo &TII); 85 86 protected: 87 /// Helper function for weight calculations. 88 /// (Re)compute LI's spill weight and allocation hint, or, for non null 89 /// start and end - compute future expected spill weight of a split 90 /// artifact of LI that will span between start and end slot indexes. 91 /// \param LI The live interval for which to compute the weight. 92 /// \param Start The expected beginning of the split artifact. Instructions 93 /// before start will not affect the weight. Relevant for 94 /// weight calculation of future split artifact. 95 /// \param End The expected end of the split artifact. Instructions 96 /// after end will not affect the weight. Relevant for 97 /// weight calculation of future split artifact. 98 /// \return The spill weight. Returns negative weight for unspillable LI. 99 float weightCalcHelper(LiveInterval &LI, SlotIndex *Start = nullptr, 100 SlotIndex *End = nullptr); 101 102 /// Weight normalization function. 103 virtual float normalize(float UseDefFreq, unsigned Size, 104 unsigned NumInstr) { 105 return normalizeSpillWeight(UseDefFreq, Size, NumInstr); 106 } 107 }; 108 } // end namespace llvm 109 110 #endif // LLVM_CODEGEN_CALCSPILLWEIGHTS_H 111