1//===- MachineSSAUpdater.h - Unstructured SSA Update Tool -------*- 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 declares the MachineSSAUpdater class.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_CODEGEN_MACHINESSAUPDATER_H
14#define LLVM_CODEGEN_MACHINESSAUPDATER_H
15
16namespace llvm {
17
18class MachineBasicBlock;
19class MachineFunction;
20class MachineInstr;
21class MachineOperand;
22class MachineRegisterInfo;
23class TargetInstrInfo;
24class TargetRegisterClass;
25template<typename T> class SmallVectorImpl;
26template<typename T> class SSAUpdaterTraits;
27
28/// MachineSSAUpdater - This class updates SSA form for a set of virtual
29/// registers defined in multiple blocks.  This is used when code duplication
30/// or another unstructured transformation wants to rewrite a set of uses of one
31/// vreg with uses of a set of vregs.
32class MachineSSAUpdater {
33  friend class SSAUpdaterTraits<MachineSSAUpdater>;
34
35private:
36  /// AvailableVals - This keeps track of which value to use on a per-block
37  /// basis.  When we insert PHI nodes, we keep track of them here.
38  //typedef DenseMap<MachineBasicBlock*, unsigned > AvailableValsTy;
39  void *AV = nullptr;
40
41  /// VR - Current virtual register whose uses are being updated.
42  unsigned VR;
43
44  /// VRC - Register class of the current virtual register.
45  const TargetRegisterClass *VRC;
46
47  /// InsertedPHIs - If this is non-null, the MachineSSAUpdater adds all PHI
48  /// nodes that it creates to the vector.
49  SmallVectorImpl<MachineInstr*> *InsertedPHIs;
50
51  const TargetInstrInfo *TII;
52  MachineRegisterInfo *MRI;
53
54public:
55  /// MachineSSAUpdater constructor.  If InsertedPHIs is specified, it will be
56  /// filled in with all PHI Nodes created by rewriting.
57  explicit MachineSSAUpdater(MachineFunction &MF,
58                        SmallVectorImpl<MachineInstr*> *NewPHI = nullptr);
59  MachineSSAUpdater(const MachineSSAUpdater &) = delete;
60  MachineSSAUpdater &operator=(const MachineSSAUpdater &) = delete;
61  ~MachineSSAUpdater();
62
63  /// Initialize - Reset this object to get ready for a new set of SSA
64  /// updates.
65  void Initialize(unsigned V);
66
67  /// AddAvailableValue - Indicate that a rewritten value is available at the
68  /// end of the specified block with the specified value.
69  void AddAvailableValue(MachineBasicBlock *BB, unsigned V);
70
71  /// HasValueForBlock - Return true if the MachineSSAUpdater already has a
72  /// value for the specified block.
73  bool HasValueForBlock(MachineBasicBlock *BB) const;
74
75  /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
76  /// live at the end of the specified block.
77  unsigned GetValueAtEndOfBlock(MachineBasicBlock *BB);
78
79  /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
80  /// is live in the middle of the specified block.
81  ///
82  /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
83  /// important case: if there is a definition of the rewritten value after the
84  /// 'use' in BB.  Consider code like this:
85  ///
86  ///      X1 = ...
87  ///   SomeBB:
88  ///      use(X)
89  ///      X2 = ...
90  ///      br Cond, SomeBB, OutBB
91  ///
92  /// In this case, there are two values (X1 and X2) added to the AvailableVals
93  /// set by the client of the rewriter, and those values are both live out of
94  /// their respective blocks.  However, the use of X happens in the *middle* of
95  /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
96  /// merge the appropriate values, and this value isn't live out of the block.
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  unsigned GetValueAtEndOfBlockInternal(MachineBasicBlock *BB);
108};
109
110} // end namespace llvm
111
112#endif // LLVM_CODEGEN_MACHINESSAUPDATER_H
113