CalcSpillWeights.h revision 263508 
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
24  /// \brief 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  ///
34  static inline float normalizeSpillWeight(float UseDefFreq, unsigned Size) {
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  /// \brief Calculate auxiliary information for a virtual register such as its
44  /// spill weight and allocation hint.
45  class VirtRegAuxInfo {
46  public:
47    typedef float (*NormalizingFn)(float, unsigned);
48
49  private:
50    MachineFunction &MF;
51    LiveIntervals &LIS;
52    const MachineLoopInfo &Loops;
53    const MachineBlockFrequencyInfo &MBFI;
54    DenseMap<unsigned, float> Hint;
55    NormalizingFn normalize;
56
57  public:
58    VirtRegAuxInfo(MachineFunction &mf, LiveIntervals &lis,
59                   const MachineLoopInfo &loops,
60                   const MachineBlockFrequencyInfo &mbfi,
61                   NormalizingFn norm = normalizeSpillWeight)
62        : MF(mf), LIS(lis), Loops(loops), MBFI(mbfi), normalize(norm) {}
63
64    /// \brief (re)compute li's spill weight and allocation hint.
65    void calculateSpillWeightAndHint(LiveInterval &li);
66  };
67
68  /// \brief Compute spill weights and allocation hints for all virtual register
69  /// live intervals.
70  void calculateSpillWeightsAndHints(LiveIntervals &LIS, MachineFunction &MF,
71                                     const MachineLoopInfo &MLI,
72                                     const MachineBlockFrequencyInfo &MBFI,
73                                     VirtRegAuxInfo::NormalizingFn norm =
74                                         normalizeSpillWeight);
75}
76
77#endif // LLVM_CODEGEN_CALCSPILLWEIGHTS_H
78