MachineSSAUpdater.h revision 200581 
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  class MachineBasicBlock;
19  class MachineFunction;
20  class MachineInstr;
21  class MachineOperand;
22  class MachineRegisterInfo;
23  class TargetInstrInfo;
24  class TargetRegisterClass;
25  template<typename T> class SmallVectorImpl;
26
27/// MachineSSAUpdater - This class updates SSA form for a set of virtual
28/// registers defined in multiple blocks.  This is used when code duplication
29/// or another unstructured transformation wants to rewrite a set of uses of one
30/// vreg with uses of a set of vregs.
31class MachineSSAUpdater {
32  /// AvailableVals - This keeps track of which value to use on a per-block
33  /// basis.  When we insert PHI nodes, we keep track of them here.
34  //typedef DenseMap<MachineBasicBlock*, unsigned > AvailableValsTy;
35  void *AV;
36
37  /// IncomingPredInfo - We use this as scratch space when doing our recursive
38  /// walk.  This should only be used in GetValueInBlockInternal, normally it
39  /// should be empty.
40  //std::vector<std::pair<MachineBasicBlock*, unsigned > > IncomingPredInfo;
41  void *IPI;
42
43  /// VR - Current virtual register whose uses are being updated.
44  unsigned VR;
45
46  /// VRC - Register class of the current virtual register.
47  const TargetRegisterClass *VRC;
48
49  /// InsertedPHIs - If this is non-null, the MachineSSAUpdater adds all PHI
50  /// nodes that it creates to the vector.
51  SmallVectorImpl<MachineInstr*> *InsertedPHIs;
52
53  const TargetInstrInfo *TII;
54  MachineRegisterInfo *MRI;
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*> *InsertedPHIs = 0);
60  ~MachineSSAUpdater();
61
62  /// Initialize - Reset this object to get ready for a new set of SSA
63  /// updates.
64  void Initialize(unsigned V);
65
66  /// AddAvailableValue - Indicate that a rewritten value is available at the
67  /// end of the specified block with the specified value.
68  void AddAvailableValue(MachineBasicBlock *BB, unsigned V);
69
70  /// HasValueForBlock - Return true if the MachineSSAUpdater already has a
71  /// value for the specified block.
72  bool HasValueForBlock(MachineBasicBlock *BB) const;
73
74  /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
75  /// live at the end of the specified block.
76  unsigned GetValueAtEndOfBlock(MachineBasicBlock *BB);
77
78  /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
79  /// is live in the middle of the specified block.
80  ///
81  /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
82  /// important case: if there is a definition of the rewritten value after the
83  /// 'use' in BB.  Consider code like this:
84  ///
85  ///      X1 = ...
86  ///   SomeBB:
87  ///      use(X)
88  ///      X2 = ...
89  ///      br Cond, SomeBB, OutBB
90  ///
91  /// In this case, there are two values (X1 and X2) added to the AvailableVals
92  /// set by the client of the rewriter, and those values are both live out of
93  /// their respective blocks.  However, the use of X happens in the *middle* of
94  /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
95  /// merge the appropriate values, and this value isn't live out of the block.
96  ///
97  unsigned GetValueInMiddleOfBlock(MachineBasicBlock *BB);
98
99  /// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
100  /// which use their value in the corresponding predecessor.  Note that this
101  /// will not work if the use is supposed to be rewritten to a value defined in
102  /// the same block as the use, but above it.  Any 'AddAvailableValue's added
103  /// for the use's block will be considered to be below it.
104  void RewriteUse(MachineOperand &U);
105
106private:
107  void ReplaceRegWith(unsigned OldReg, unsigned NewReg);
108  unsigned GetValueAtEndOfBlockInternal(MachineBasicBlock *BB);
109  void operator=(const MachineSSAUpdater&); // DO NOT IMPLEMENT
110  MachineSSAUpdater(const MachineSSAUpdater&);     // DO NOT IMPLEMENT
111};
112
113} // End llvm namespace
114
115#endif
116