MachineSSAUpdater.h revision 341825 
1//===- MachineSSAUpdater.h - Unstructured SSA Update Tool -------*- 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 declares the MachineSSAUpdater class.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_CODEGEN_MACHINESSAUPDATER_H
15#define LLVM_CODEGEN_MACHINESSAUPDATER_H
16
17namespace llvm {
18
19class MachineBasicBlock;
20class MachineFunction;
21class MachineInstr;
22class MachineOperand;
23class MachineRegisterInfo;
24class TargetInstrInfo;
25class TargetRegisterClass;
26template<typename T> class SmallVectorImpl;
27template<typename T> class SSAUpdaterTraits;
28
29/// MachineSSAUpdater - This class updates SSA form for a set of virtual
30/// registers defined in multiple blocks.  This is used when code duplication
31/// or another unstructured transformation wants to rewrite a set of uses of one
32/// vreg with uses of a set of vregs.
33class MachineSSAUpdater {
34  friend class SSAUpdaterTraits<MachineSSAUpdater>;
35
36private:
37  /// AvailableVals - This keeps track of which value to use on a per-block
38  /// basis.  When we insert PHI nodes, we keep track of them here.
39  //typedef DenseMap<MachineBasicBlock*, unsigned > AvailableValsTy;
40  void *AV = nullptr;
41
42  /// VR - Current virtual register whose uses are being updated.
43  unsigned VR;
44
45  /// VRC - Register class of the current virtual register.
46  const TargetRegisterClass *VRC;
47
48  /// InsertedPHIs - If this is non-null, the MachineSSAUpdater adds all PHI
49  /// nodes that it creates to the vector.
50  SmallVectorImpl<MachineInstr*> *InsertedPHIs;
51
52  const TargetInstrInfo *TII;
53  MachineRegisterInfo *MRI;
54
55public:
56  /// MachineSSAUpdater constructor.  If InsertedPHIs is specified, it will be
57  /// filled in with all PHI Nodes created by rewriting.
58  explicit MachineSSAUpdater(MachineFunction &MF,
59                        SmallVectorImpl<MachineInstr*> *NewPHI = nullptr);
60  MachineSSAUpdater(const MachineSSAUpdater &) = delete;
61  MachineSSAUpdater &operator=(const MachineSSAUpdater &) = delete;
62  ~MachineSSAUpdater();
63
64  /// Initialize - Reset this object to get ready for a new set of SSA
65  /// updates.
66  void Initialize(unsigned V);
67
68  /// AddAvailableValue - Indicate that a rewritten value is available at the
69  /// end of the specified block with the specified value.
70  void AddAvailableValue(MachineBasicBlock *BB, unsigned V);
71
72  /// HasValueForBlock - Return true if the MachineSSAUpdater already has a
73  /// value for the specified block.
74  bool HasValueForBlock(MachineBasicBlock *BB) const;
75
76  /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
77  /// live at the end of the specified block.
78  unsigned GetValueAtEndOfBlock(MachineBasicBlock *BB);
79
80  /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
81  /// is live in the middle of the specified block.
82  ///
83  /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
84  /// important case: if there is a definition of the rewritten value after the
85  /// 'use' in BB.  Consider code like this:
86  ///
87  ///      X1 = ...
88  ///   SomeBB:
89  ///      use(X)
90  ///      X2 = ...
91  ///      br Cond, SomeBB, OutBB
92  ///
93  /// In this case, there are two values (X1 and X2) added to the AvailableVals
94  /// set by the client of the rewriter, and those values are both live out of
95  /// their respective blocks.  However, the use of X happens in the *middle* of
96  /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
97  /// merge the appropriate values, and this value isn't live out of the block.
98  unsigned GetValueInMiddleOfBlock(MachineBasicBlock *BB);
99
100  /// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
101  /// which use their value in the corresponding predecessor.  Note that this
102  /// will not work if the use is supposed to be rewritten to a value defined in
103  /// the same block as the use, but above it.  Any 'AddAvailableValue's added
104  /// for the use's block will be considered to be below it.
105  void RewriteUse(MachineOperand &U);
106
107private:
108  unsigned GetValueAtEndOfBlockInternal(MachineBasicBlock *BB);
109};
110
111} // end namespace llvm
112
113#endif // LLVM_CODEGEN_MACHINESSAUPDATER_H
114