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 VirtRegMap; 22 23 /// Normalize the spill weight of a live interval 24 /// 25 /// The spill weight of a live interval is computed as: 26 /// 27 /// (sum(use freq) + sum(def freq)) / (K + size) 28 /// 29 /// @param UseDefFreq Expected number of executed use and def instructions 30 /// per function call. Derived from block frequencies. 31 /// @param Size Size of live interval as returnexd by getSize() 32 /// @param NumInstr Number of instructions using this live interval normalizeSpillWeight(float UseDefFreq,unsigned Size,unsigned NumInstr)33 static inline float normalizeSpillWeight(float UseDefFreq, unsigned Size, 34 unsigned NumInstr) { 35 // The constant 25 instructions is added to avoid depending too much on 36 // accidental SlotIndex gaps for small intervals. The effect is that small 37 // intervals have a spill weight that is mostly proportional to the number 38 // of uses, while large intervals get a spill weight that is closer to a use 39 // density. 40 return UseDefFreq / (Size + 25*SlotIndex::InstrDist); 41 } 42 43 /// Calculate auxiliary information for a virtual register such as its 44 /// spill weight and allocation hint. 45 class VirtRegAuxInfo { 46 MachineFunction &MF; 47 LiveIntervals &LIS; 48 const VirtRegMap &VRM; 49 const MachineLoopInfo &Loops; 50 const MachineBlockFrequencyInfo &MBFI; 51 52 /// Returns true if Reg of live interval LI is used in instruction with many 53 /// operands like STATEPOINT. 54 bool isLiveAtStatepointVarArg(LiveInterval &LI); 55 56 public: VirtRegAuxInfo(MachineFunction & MF,LiveIntervals & LIS,const VirtRegMap & VRM,const MachineLoopInfo & Loops,const MachineBlockFrequencyInfo & MBFI)57 VirtRegAuxInfo(MachineFunction &MF, LiveIntervals &LIS, 58 const VirtRegMap &VRM, const MachineLoopInfo &Loops, 59 const MachineBlockFrequencyInfo &MBFI) 60 : MF(MF), LIS(LIS), VRM(VRM), Loops(Loops), MBFI(MBFI) {} 61 62 virtual ~VirtRegAuxInfo() = default; 63 64 /// (re)compute li's spill weight and allocation hint. 65 void calculateSpillWeightAndHint(LiveInterval &LI); 66 67 /// Compute spill weights and allocation hints for all virtual register 68 /// live intervals. 69 void calculateSpillWeightsAndHints(); 70 71 /// Return the preferred allocation register for reg, given a COPY 72 /// instruction. 73 static Register copyHint(const MachineInstr *MI, unsigned Reg, 74 const TargetRegisterInfo &TRI, 75 const MachineRegisterInfo &MRI); 76 77 /// Determine if all values in LI are rematerializable. 78 static bool isRematerializable(const LiveInterval &LI, 79 const LiveIntervals &LIS, 80 const VirtRegMap &VRM, 81 const TargetInstrInfo &TII); 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. normalize(float UseDefFreq,unsigned Size,unsigned NumInstr)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