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 
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   /// @param NumInstr   Number of instructions using this live interval
34   ///
normalizeSpillWeight(float UseDefFreq,unsigned Size,unsigned NumInstr)35   static inline float normalizeSpillWeight(float UseDefFreq, unsigned Size,
36                                            unsigned NumInstr) {
37     // The constant 25 instructions is added to avoid depending too much on
38     // accidental SlotIndex gaps for small intervals. The effect is that small
39     // intervals have a spill weight that is mostly proportional to the number
40     // of uses, while large intervals get a spill weight that is closer to a use
41     // density.
42     return UseDefFreq / (Size + 25*SlotIndex::InstrDist);
43   }
44 
45   /// \brief Calculate auxiliary information for a virtual register such as its
46   /// spill weight and allocation hint.
47   class VirtRegAuxInfo {
48   public:
49     typedef float (*NormalizingFn)(float, unsigned, unsigned);
50 
51   private:
52     MachineFunction &MF;
53     LiveIntervals &LIS;
54     const MachineLoopInfo &Loops;
55     const MachineBlockFrequencyInfo &MBFI;
56     DenseMap<unsigned, float> Hint;
57     NormalizingFn normalize;
58 
59   public:
60     VirtRegAuxInfo(MachineFunction &mf, LiveIntervals &lis,
61                    const MachineLoopInfo &loops,
62                    const MachineBlockFrequencyInfo &mbfi,
63                    NormalizingFn norm = normalizeSpillWeight)
MF(mf)64         : MF(mf), LIS(lis), Loops(loops), MBFI(mbfi), normalize(norm) {}
65 
66     /// \brief (re)compute li's spill weight and allocation hint.
67     void calculateSpillWeightAndHint(LiveInterval &li);
68   };
69 
70   /// \brief Compute spill weights and allocation hints for all virtual register
71   /// live intervals.
72   void calculateSpillWeightsAndHints(LiveIntervals &LIS, MachineFunction &MF,
73                                      const MachineLoopInfo &MLI,
74                                      const MachineBlockFrequencyInfo &MBFI,
75                                      VirtRegAuxInfo::NormalizingFn norm =
76                                          normalizeSpillWeight);
77 }
78 
79 #endif // LLVM_CODEGEN_CALCSPILLWEIGHTS_H
80