1//===---------------- lib/CodeGen/CalcSpillWeights.h ------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9
10
11#ifndef LLVM_CODEGEN_CALCSPILLWEIGHTS_H
12#define LLVM_CODEGEN_CALCSPILLWEIGHTS_H
13
14#include "llvm/ADT/DenseMap.h"
15#include "llvm/CodeGen/SlotIndexes.h"
16
17namespace llvm {
18
19  class LiveInterval;
20  class LiveIntervals;
21  class MachineBlockFrequencyInfo;
22  class MachineLoopInfo;
23  class VirtRegMap;
24
25  /// \brief Normalize the spill weight of a live interval
26  ///
27  /// The spill weight of a live interval is computed as:
28  ///
29  ///   (sum(use freq) + sum(def freq)) / (K + size)
30  ///
31  /// @param UseDefFreq Expected number of executed use and def instructions
32  ///                   per function call. Derived from block frequencies.
33  /// @param Size       Size of live interval as returnexd by getSize()
34  /// @param NumInstr   Number of instructions using this live interval
35  ///
36  static inline float normalizeSpillWeight(float UseDefFreq, unsigned Size,
37                                           unsigned NumInstr) {
38    // The constant 25 instructions is added to avoid depending too much on
39    // accidental SlotIndex gaps for small intervals. The effect is that small
40    // intervals have a spill weight that is mostly proportional to the number
41    // of uses, while large intervals get a spill weight that is closer to a use
42    // density.
43    return UseDefFreq / (Size + 25*SlotIndex::InstrDist);
44  }
45
46  /// \brief Calculate auxiliary information for a virtual register such as its
47  /// spill weight and allocation hint.
48  class VirtRegAuxInfo {
49  public:
50    typedef float (*NormalizingFn)(float, unsigned, unsigned);
51
52  private:
53    MachineFunction &MF;
54    LiveIntervals &LIS;
55    VirtRegMap *VRM;
56    const MachineLoopInfo &Loops;
57    const MachineBlockFrequencyInfo &MBFI;
58    DenseMap<unsigned, float> Hint;
59    NormalizingFn normalize;
60
61  public:
62    VirtRegAuxInfo(MachineFunction &mf, LiveIntervals &lis,
63                   VirtRegMap *vrm, const MachineLoopInfo &loops,
64                   const MachineBlockFrequencyInfo &mbfi,
65                   NormalizingFn norm = normalizeSpillWeight)
66        : MF(mf), LIS(lis), VRM(vrm), Loops(loops), MBFI(mbfi), normalize(norm) {}
67
68    /// \brief (re)compute li's spill weight and allocation hint.
69    void calculateSpillWeightAndHint(LiveInterval &li);
70  };
71
72  /// \brief Compute spill weights and allocation hints for all virtual register
73  /// live intervals.
74  void calculateSpillWeightsAndHints(LiveIntervals &LIS, MachineFunction &MF,
75                                     VirtRegMap *VRM,
76                                     const MachineLoopInfo &MLI,
77                                     const MachineBlockFrequencyInfo &MBFI,
78                                     VirtRegAuxInfo::NormalizingFn norm =
79                                         normalizeSpillWeight);
80}
81
82#endif // LLVM_CODEGEN_CALCSPILLWEIGHTS_H
83