LLVM  8.0.0svn
MachineSSAUpdater.h
Go to the documentation of this file.
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 
17 namespace llvm {
18 
19 class MachineBasicBlock;
20 class MachineFunction;
21 class MachineInstr;
22 class MachineOperand;
23 class MachineRegisterInfo;
24 class TargetInstrInfo;
25 class TargetRegisterClass;
26 template<typename T> class SmallVectorImpl;
27 template<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.
35 
36 private:
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;
54 
55 public:
56  /// MachineSSAUpdater constructor. If InsertedPHIs is specified, it will be
57  /// filled in with all PHI Nodes created by rewriting.
59  SmallVectorImpl<MachineInstr*> *NewPHI = nullptr);
60  MachineSSAUpdater(const MachineSSAUpdater &) = delete;
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.
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.
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 
107 private:
108  unsigned GetValueAtEndOfBlockInternal(MachineBasicBlock *BB);
109 };
110 
111 } // end namespace llvm
112 
113 #endif // LLVM_CODEGEN_MACHINESSAUPDATER_H
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
void RewriteUse(MachineOperand &U)
RewriteUse - Rewrite a use of the symbolic value.
MachineSSAUpdater - This class updates SSA form for a set of virtual registers defined in multiple bl...
unsigned GetValueAtEndOfBlock(MachineBasicBlock *BB)
GetValueAtEndOfBlock - Construct SSA form, materializing a value that is live at the end of the speci...
const HexagonInstrInfo * TII
MachineSSAUpdater(MachineFunction &MF, SmallVectorImpl< MachineInstr *> *NewPHI=nullptr)
MachineSSAUpdater constructor.
void Initialize(unsigned V)
Initialize - Reset this object to get ready for a new set of SSA updates.
MachineSSAUpdater & operator=(const MachineSSAUpdater &)=delete
TargetInstrInfo - Interface to description of machine instruction set.
unsigned const MachineRegisterInfo * MRI
MachineOperand class - Representation of each machine instruction operand.
MachineRegisterInfo - Keep track of information for virtual and physical registers, including vreg register classes, use/def chains for registers, etc.
bool HasValueForBlock(MachineBasicBlock *BB) const
HasValueForBlock - Return true if the MachineSSAUpdater already has a value for the specified block...
unsigned GetValueInMiddleOfBlock(MachineBasicBlock *BB)
GetValueInMiddleOfBlock - Construct SSA form, materializing a value that is live in the middle of the...
void AddAvailableValue(MachineBasicBlock *BB, unsigned V)
AddAvailableValue - Indicate that a rewritten value is available at the end of the specified block wi...