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
14namespace llvm {
15
16class LiveInterval;
17class LiveIntervals;
18class MachineBlockFrequencyInfo;
19class MachineFunction;
20class MachineLoopInfo;
21class 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
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:
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.
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