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 
17 namespace 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   ///
normalizeSpillWeight(float UseDefFreq,unsigned Size,unsigned NumInstr)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)
MF(mf)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