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:
CoalescerPair(const TargetRegisterInfo & tri)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().
CoalescerPair(unsigned VirtReg,unsigned PhysReg,const TargetRegisterInfo & tri)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.
isPhys()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.
isPartial()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.
isCrossClass()92     bool isCrossClass() const { return CrossClass; }
93 
94     /// Return true when getSrcReg is the register being defined by
95     /// the original copy instruction.
isFlipped()96     bool isFlipped() const { return Flipped; }
97 
98     /// Return the register (virtual or physical) that will remain
99     /// after coalescing.
getDstReg()100     unsigned getDstReg() const { return DstReg; }
101 
102     /// Return the virtual register that will be coalesced away.
getSrcReg()103     unsigned getSrcReg() const { return SrcReg; }
104 
105     /// Return the subregister index that DstReg will be coalesced into, or 0.
getDstIdx()106     unsigned getDstIdx() const { return DstIdx; }
107 
108     /// Return the subregister index that SrcReg will be coalesced into, or 0.
getSrcIdx()109     unsigned getSrcIdx() const { return SrcIdx; }
110 
111     /// Return the register class of the coalesced register.
getNewRC()112     const TargetRegisterClass *getNewRC() const { return NewRC; }
113   };
114 } // End llvm namespace
115 
116 #endif
117