llvm/lib/CodeGen/RegisterCoalescer.h

   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