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      1 //===- RegisterCoalescer.h - Register Coalescing Interface ------*- C++ -*-===//
      2 //
      3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
      4 // See https://llvm.org/LICENSE.txt for license information.
      5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
      6 //
      7 //===----------------------------------------------------------------------===//
      8 //
      9 // This file contains the abstract interface for register coalescers,
     10 // allowing them to interact with and query register allocators.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #ifndef LLVM_LIB_CODEGEN_REGISTERCOALESCER_H
     15 #define LLVM_LIB_CODEGEN_REGISTERCOALESCER_H
     16 
     17 #include "llvm/CodeGen/Register.h"
     18 
     19 namespace llvm {
     20 
     21 class MachineInstr;
     22 class TargetRegisterClass;
     23 class TargetRegisterInfo;
     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     Register DstReg;
     34 
     35     /// The virtual register that will be coalesced into dstReg.
     36     Register SrcReg;
     37 
     38     /// The sub-register index of the old DstReg in the new coalesced register.
     39     unsigned DstIdx = 0;
     40 
     41     /// The sub-register index of the old SrcReg in the new coalesced register.
     42     unsigned SrcIdx = 0;
     43 
     44     /// True when the original copy was a partial subregister copy.
     45     bool Partial = false;
     46 
     47     /// True when both regs are virtual and newRC is constrained.
     48     bool CrossClass = false;
     49 
     50     /// True when DstReg and SrcReg are reversed from the original
     51     /// copy instruction.
     52     bool Flipped = false;
     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 = nullptr;
     58 
     59   public:
     60     CoalescerPair(const TargetRegisterInfo &tri) : TRI(tri) {}
     61 
     62     /// Create a CoalescerPair representing a virtreg-to-physreg copy.
     63     /// No need to call setRegisters().
     64     CoalescerPair(Register VirtReg, MCRegister PhysReg,
     65                   const TargetRegisterInfo &tri)
     66         : TRI(tri), DstReg(PhysReg), SrcReg(VirtReg) {}
     67 
     68     /// Set registers to match the copy instruction MI. Return
     69     /// false if MI is not a coalescable copy instruction.
     70     bool setRegisters(const MachineInstr*);
     71 
     72     /// Swap SrcReg and DstReg. Return false if swapping is impossible
     73     /// because DstReg is a physical register, or SubIdx is set.
     74     bool flip();
     75 
     76     /// Return true if MI is a copy instruction that will become
     77     /// an identity copy after coalescing.
     78     bool isCoalescable(const MachineInstr*) const;
     79 
     80     /// Return true if DstReg is a physical register.
     81     bool isPhys() const { return !NewRC; }
     82 
     83     /// Return true if the original copy instruction did not copy
     84     /// the full register, but was a subreg operation.
     85     bool isPartial() const { return Partial; }
     86 
     87     /// Return true if DstReg is virtual and NewRC is a smaller
     88     /// register class than DstReg's.
     89     bool isCrossClass() const { return CrossClass; }
     90 
     91     /// Return true when getSrcReg is the register being defined by
     92     /// the original copy instruction.
     93     bool isFlipped() const { return Flipped; }
     94 
     95     /// Return the register (virtual or physical) that will remain
     96     /// after coalescing.
     97     Register getDstReg() const { return DstReg; }
     98 
     99     /// Return the virtual register that will be coalesced away.
    100     Register getSrcReg() const { return SrcReg; }
    101 
    102     /// Return the subregister index that DstReg will be coalesced into, or 0.
    103     unsigned getDstIdx() const { return DstIdx; }
    104 
    105     /// Return the subregister index that SrcReg will be coalesced into, or 0.
    106     unsigned getSrcIdx() const { return SrcIdx; }
    107 
    108     /// Return the register class of the coalesced register.
    109     const TargetRegisterClass *getNewRC() const { return NewRC; }
    110   };
    111 
    112 } // end namespace llvm
    113 
    114 #endif // LLVM_LIB_CODEGEN_REGISTERCOALESCER_H
    115