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      1 //===---- LiveRangeEdit.h - Basic tools for split and spill -----*- 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 // The LiveRangeEdit class represents changes done to a virtual register when it
     11 // is spilled or split.
     12 //
     13 // The parent register is never changed. Instead, a number of new virtual
     14 // registers are created and added to the newRegs vector.
     15 //
     16 //===----------------------------------------------------------------------===//
     17 
     18 #ifndef LLVM_CODEGEN_LIVERANGEEDIT_H
     19 #define LLVM_CODEGEN_LIVERANGEEDIT_H
     20 
     21 #include "llvm/ADT/ArrayRef.h"
     22 #include "llvm/ADT/SetVector.h"
     23 #include "llvm/ADT/SmallPtrSet.h"
     24 #include "llvm/CodeGen/LiveInterval.h"
     25 #include "llvm/CodeGen/MachineRegisterInfo.h"
     26 #include "llvm/Target/TargetMachine.h"
     27 
     28 namespace llvm {
     29 
     30 class AliasAnalysis;
     31 class LiveIntervals;
     32 class MachineBlockFrequencyInfo;
     33 class MachineLoopInfo;
     34 class VirtRegMap;
     35 
     36 class LiveRangeEdit : private MachineRegisterInfo::Delegate {
     37 public:
     38   /// Callback methods for LiveRangeEdit owners.
     39   class Delegate {
     40     virtual void anchor();
     41   public:
     42     /// Called immediately before erasing a dead machine instruction.
     43     virtual void LRE_WillEraseInstruction(MachineInstr *MI) {}
     44 
     45     /// Called when a virtual register is no longer used. Return false to defer
     46     /// its deletion from LiveIntervals.
     47     virtual bool LRE_CanEraseVirtReg(unsigned) { return true; }
     48 
     49     /// Called before shrinking the live range of a virtual register.
     50     virtual void LRE_WillShrinkVirtReg(unsigned) {}
     51 
     52     /// Called after cloning a virtual register.
     53     /// This is used for new registers representing connected components of Old.
     54     virtual void LRE_DidCloneVirtReg(unsigned New, unsigned Old) {}
     55 
     56     virtual ~Delegate() {}
     57   };
     58 
     59 private:
     60   LiveInterval *Parent;
     61   SmallVectorImpl<unsigned> &NewRegs;
     62   MachineRegisterInfo &MRI;
     63   LiveIntervals &LIS;
     64   VirtRegMap *VRM;
     65   const TargetInstrInfo &TII;
     66   Delegate *const TheDelegate;
     67 
     68   /// FirstNew - Index of the first register added to NewRegs.
     69   const unsigned FirstNew;
     70 
     71   /// ScannedRemattable - true when remattable values have been identified.
     72   bool ScannedRemattable;
     73 
     74   /// Remattable - Values defined by remattable instructions as identified by
     75   /// tii.isTriviallyReMaterializable().
     76   SmallPtrSet<const VNInfo*,4> Remattable;
     77 
     78   /// Rematted - Values that were actually rematted, and so need to have their
     79   /// live range trimmed or entirely removed.
     80   SmallPtrSet<const VNInfo*,4> Rematted;
     81 
     82   /// scanRemattable - Identify the Parent values that may rematerialize.
     83   void scanRemattable(AliasAnalysis *aa);
     84 
     85   /// allUsesAvailableAt - Return true if all registers used by OrigMI at
     86   /// OrigIdx are also available with the same value at UseIdx.
     87   bool allUsesAvailableAt(const MachineInstr *OrigMI, SlotIndex OrigIdx,
     88                           SlotIndex UseIdx) const;
     89 
     90   /// foldAsLoad - If LI has a single use and a single def that can be folded as
     91   /// a load, eliminate the register by folding the def into the use.
     92   bool foldAsLoad(LiveInterval *LI, SmallVectorImpl<MachineInstr*> &Dead);
     93 
     94   typedef SetVector<LiveInterval*,
     95                     SmallVector<LiveInterval*, 8>,
     96                     SmallPtrSet<LiveInterval*, 8> > ToShrinkSet;
     97   /// Helper for eliminateDeadDefs.
     98   void eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink);
     99 
    100   /// MachineRegisterInfo callback to notify when new virtual
    101   /// registers are created.
    102   void MRI_NoteNewVirtualRegister(unsigned VReg) override;
    103 
    104 public:
    105   /// Create a LiveRangeEdit for breaking down parent into smaller pieces.
    106   /// @param parent The register being spilled or split.
    107   /// @param newRegs List to receive any new registers created. This needn't be
    108   ///                empty initially, any existing registers are ignored.
    109   /// @param MF The MachineFunction the live range edit is taking place in.
    110   /// @param lis The collection of all live intervals in this function.
    111   /// @param vrm Map of virtual registers to physical registers for this
    112   ///            function.  If NULL, no virtual register map updates will
    113   ///            be done.  This could be the case if called before Regalloc.
    114   LiveRangeEdit(LiveInterval *parent,
    115                 SmallVectorImpl<unsigned> &newRegs,
    116                 MachineFunction &MF,
    117                 LiveIntervals &lis,
    118                 VirtRegMap *vrm,
    119                 Delegate *delegate = nullptr)
    120     : Parent(parent), NewRegs(newRegs),
    121       MRI(MF.getRegInfo()), LIS(lis), VRM(vrm),
    122       TII(*MF.getTarget().getInstrInfo()),
    123       TheDelegate(delegate),
    124       FirstNew(newRegs.size()),
    125       ScannedRemattable(false) { MRI.setDelegate(this); }
    126 
    127   ~LiveRangeEdit() { MRI.resetDelegate(this); }
    128 
    129   LiveInterval &getParent() const {
    130    assert(Parent && "No parent LiveInterval");
    131    return *Parent;
    132   }
    133   unsigned getReg() const { return getParent().reg; }
    134 
    135   /// Iterator for accessing the new registers added by this edit.
    136   typedef SmallVectorImpl<unsigned>::const_iterator iterator;
    137   iterator begin() const { return NewRegs.begin()+FirstNew; }
    138   iterator end() const { return NewRegs.end(); }
    139   unsigned size() const { return NewRegs.size()-FirstNew; }
    140   bool empty() const { return size() == 0; }
    141   unsigned get(unsigned idx) const { return NewRegs[idx+FirstNew]; }
    142 
    143   ArrayRef<unsigned> regs() const {
    144     return makeArrayRef(NewRegs).slice(FirstNew);
    145   }
    146 
    147   /// createEmptyIntervalFrom - Create a new empty interval based on OldReg.
    148   LiveInterval &createEmptyIntervalFrom(unsigned OldReg);
    149 
    150   /// createFrom - Create a new virtual register based on OldReg.
    151   unsigned createFrom(unsigned OldReg);
    152 
    153   /// create - Create a new register with the same class and original slot as
    154   /// parent.
    155   LiveInterval &createEmptyInterval() {
    156     return createEmptyIntervalFrom(getReg());
    157   }
    158 
    159   unsigned create() {
    160     return createFrom(getReg());
    161   }
    162 
    163   /// anyRematerializable - Return true if any parent values may be
    164   /// rematerializable.
    165   /// This function must be called before any rematerialization is attempted.
    166   bool anyRematerializable(AliasAnalysis*);
    167 
    168   /// checkRematerializable - Manually add VNI to the list of rematerializable
    169   /// values if DefMI may be rematerializable.
    170   bool checkRematerializable(VNInfo *VNI, const MachineInstr *DefMI,
    171                              AliasAnalysis*);
    172 
    173   /// Remat - Information needed to rematerialize at a specific location.
    174   struct Remat {
    175     VNInfo *ParentVNI;      // parent_'s value at the remat location.
    176     MachineInstr *OrigMI;   // Instruction defining ParentVNI.
    177     explicit Remat(VNInfo *ParentVNI) : ParentVNI(ParentVNI), OrigMI(nullptr) {}
    178   };
    179 
    180   /// canRematerializeAt - Determine if ParentVNI can be rematerialized at
    181   /// UseIdx. It is assumed that parent_.getVNINfoAt(UseIdx) == ParentVNI.
    182   /// When cheapAsAMove is set, only cheap remats are allowed.
    183   bool canRematerializeAt(Remat &RM,
    184                           SlotIndex UseIdx,
    185                           bool cheapAsAMove);
    186 
    187   /// rematerializeAt - Rematerialize RM.ParentVNI into DestReg by inserting an
    188   /// instruction into MBB before MI. The new instruction is mapped, but
    189   /// liveness is not updated.
    190   /// Return the SlotIndex of the new instruction.
    191   SlotIndex rematerializeAt(MachineBasicBlock &MBB,
    192                             MachineBasicBlock::iterator MI,
    193                             unsigned DestReg,
    194                             const Remat &RM,
    195                             const TargetRegisterInfo&,
    196                             bool Late = false);
    197 
    198   /// markRematerialized - explicitly mark a value as rematerialized after doing
    199   /// it manually.
    200   void markRematerialized(const VNInfo *ParentVNI) {
    201     Rematted.insert(ParentVNI);
    202   }
    203 
    204   /// didRematerialize - Return true if ParentVNI was rematerialized anywhere.
    205   bool didRematerialize(const VNInfo *ParentVNI) const {
    206     return Rematted.count(ParentVNI);
    207   }
    208 
    209   /// eraseVirtReg - Notify the delegate that Reg is no longer in use, and try
    210   /// to erase it from LIS.
    211   void eraseVirtReg(unsigned Reg);
    212 
    213   /// eliminateDeadDefs - Try to delete machine instructions that are now dead
    214   /// (allDefsAreDead returns true). This may cause live intervals to be trimmed
    215   /// and further dead efs to be eliminated.
    216   /// RegsBeingSpilled lists registers currently being spilled by the register
    217   /// allocator.  These registers should not be split into new intervals
    218   /// as currently those new intervals are not guaranteed to spill.
    219   void eliminateDeadDefs(SmallVectorImpl<MachineInstr*> &Dead,
    220                          ArrayRef<unsigned> RegsBeingSpilled = None);
    221 
    222   /// calculateRegClassAndHint - Recompute register class and hint for each new
    223   /// register.
    224   void calculateRegClassAndHint(MachineFunction&,
    225                                 const MachineLoopInfo&,
    226                                 const MachineBlockFrequencyInfo&);
    227 };
    228 
    229 }
    230 
    231 #endif
    232