lib/CodeGen/RegisterCoalescer.h

   1 //===-- RegisterCoalescer.h - Register Coalescing Interface -----*- 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 // This file contains the abstract interface for register coalescers,
  11 // allowing them to interact with and query register allocators.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #ifndef LLVM_LIB_CODEGEN_REGISTERCOALESCER_H
  16 #define LLVM_LIB_CODEGEN_REGISTERCOALESCER_H
  17
  18 namespace llvm {
  19
  20   class MachineInstr;
  21   class TargetRegisterInfo;
  22   class TargetRegisterClass;
  23   class TargetInstrInfo;
  24
  25   /// A helper class for register coalescers. When deciding if
  26   /// two registers can be coalesced, CoalescerPair can determine if a copy
  27   /// instruction would become an identity copy after coalescing.
  28   class CoalescerPair {
  29     const TargetRegisterInfo &TRI;
  30
  31     /// The register that will be left after coalescing. It can be a
  32     /// virtual or physical register.
  33     unsigned DstReg;
  34
  35     /// The virtual register that will be coalesced into dstReg.
  36     unsigned SrcReg;
  37
  38     /// The sub-register index of the old DstReg in the new coalesced register.
  39     unsigned DstIdx;
  40
  41     /// The sub-register index of the old SrcReg in the new coalesced register.
  42     unsigned SrcIdx;
  43
  44     /// True when the original copy was a partial subregister copy.
  45     bool Partial;
  46
  47     /// True when both regs are virtual and newRC is constrained.
  48     bool CrossClass;
  49
  50     /// True when DstReg and SrcReg are reversed from the original
  51     /// copy instruction.
  52     bool Flipped;
  53
  54     /// The register class of the coalesced register, or NULL if DstReg
  55     /// is a physreg. This register class may be a super-register of both
  56     /// SrcReg and DstReg.
  57     const TargetRegisterClass *NewRC;
  58
  59   public:
  60     CoalescerPair(const TargetRegisterInfo &tri)
  61       : TRI(tri), DstReg(0), SrcReg(0), DstIdx(0), SrcIdx(0),
  62         Partial(false), CrossClass(false), Flipped(false), NewRC(nullptr) {}
  63
  64     /// Create a CoalescerPair representing a virtreg-to-physreg copy.
  65     /// No need to call setRegisters().
  66     CoalescerPair(unsigned VirtReg, unsigned PhysReg,
  67                   const TargetRegisterInfo &tri)
  68       : TRI(tri), DstReg(PhysReg), SrcReg(VirtReg), DstIdx(0), SrcIdx(0),
  69         Partial(false), CrossClass(false), Flipped(false), NewRC(nullptr) {}
  70
  71     /// Set registers to match the copy instruction MI. Return
  72     /// false if MI is not a coalescable copy instruction.
  73     bool setRegisters(const MachineInstr*);
  74
  75     /// Swap SrcReg and DstReg. Return false if swapping is impossible
  76     /// because DstReg is a physical register, or SubIdx is set.
  77     bool flip();
  78
  79     /// Return true if MI is a copy instruction that will become
  80     /// an identity copy after coalescing.
  81     bool isCoalescable(const MachineInstr*) const;
  82
  83     /// Return true if DstReg is a physical register.
  84     bool isPhys() const { return !NewRC; }
  85
  86     /// Return true if the original copy instruction did not copy
  87     /// the full register, but was a subreg operation.
  88     bool isPartial() const { return Partial; }
  89
  90     /// Return true if DstReg is virtual and NewRC is a smaller
  91     /// register class than DstReg's.
  92     bool isCrossClass() const { return CrossClass; }
  93
  94     /// Return true when getSrcReg is the register being defined by
  95     /// the original copy instruction.
  96     bool isFlipped() const { return Flipped; }
  97
  98     /// Return the register (virtual or physical) that will remain
  99     /// after coalescing.
 100     unsigned getDstReg() const { return DstReg; }
 101
 102     /// Return the virtual register that will be coalesced away.
 103     unsigned getSrcReg() const { return SrcReg; }
 104
 105     /// Return the subregister index that DstReg will be coalesced into, or 0.
 106     unsigned getDstIdx() const { return DstIdx; }
 107
 108     /// Return the subregister index that SrcReg will be coalesced into, or 0.
 109     unsigned getSrcIdx() const { return SrcIdx; }
 110
 111     /// Return the register class of the coalesced register.
 112     const TargetRegisterClass *getNewRC() const { return NewRC; }
 113   };
 114 } // End llvm namespace
 115
 116 #endif