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
16#include "llvm/CodeGen/Register.h"
17
18namespace llvm {
19
20class MachineBasicBlock;
21class MachineFunction;
22class MachineInstr;
23class MachineOperand;
24class MachineRegisterInfo;
25class TargetInstrInfo;
26class TargetRegisterClass;
27template<typename T> class SmallVectorImpl;
28template<typename T> class SSAUpdaterTraits;
29
30/// MachineSSAUpdater - This class updates SSA form for a set of virtual
31/// registers defined in multiple blocks.  This is used when code duplication
32/// or another unstructured transformation wants to rewrite a set of uses of one
33/// vreg with uses of a set of vregs.
34class MachineSSAUpdater {
35  friend class SSAUpdaterTraits<MachineSSAUpdater>;
36
37private:
38  /// AvailableVals - This keeps track of which value to use on a per-block
39  /// basis.  When we insert PHI nodes, we keep track of them here.
40  //typedef DenseMap<MachineBasicBlock*, Register> AvailableValsTy;
41  void *AV = nullptr;
42
43  /// VRC - Register class of the current virtual register.
44  const TargetRegisterClass *VRC = nullptr;
45
46  /// InsertedPHIs - If this is non-null, the MachineSSAUpdater adds all PHI
47  /// nodes that it creates to the vector.
48  SmallVectorImpl<MachineInstr*> *InsertedPHIs;
49
50  const TargetInstrInfo *TII = nullptr;
51  MachineRegisterInfo *MRI = nullptr;
52
53public:
54  /// MachineSSAUpdater constructor.  If InsertedPHIs is specified, it will be
55  /// filled in with all PHI Nodes created by rewriting.
56  explicit MachineSSAUpdater(MachineFunction &MF,
57                        SmallVectorImpl<MachineInstr*> *NewPHI = nullptr);
58  MachineSSAUpdater(const MachineSSAUpdater &) = delete;
59  MachineSSAUpdater &operator=(const MachineSSAUpdater &) = delete;
60  ~MachineSSAUpdater();
61
62  /// Initialize - Reset this object to get ready for a new set of SSA
63  /// updates.
64  void Initialize(Register V);
65  void Initialize(const TargetRegisterClass *RC);
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, Register 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  Register GetValueAtEndOfBlock(MachineBasicBlock *BB);
78
79  /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
80  /// is live in the middle of the specified block. If ExistingValueOnly is
81  /// true then this will only return an existing value or $noreg; otherwise new
82  /// instructions may be inserted to materialize a value.
83  ///
84  /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
85  /// important case: if there is a definition of the rewritten value after the
86  /// 'use' in BB.  Consider code like this:
87  ///
88  ///      X1 = ...
89  ///   SomeBB:
90  ///      use(X)
91  ///      X2 = ...
92  ///      br Cond, SomeBB, OutBB
93  ///
94  /// In this case, there are two values (X1 and X2) added to the AvailableVals
95  /// set by the client of the rewriter, and those values are both live out of
96  /// their respective blocks.  However, the use of X happens in the *middle* of
97  /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
98  /// merge the appropriate values, and this value isn't live out of the block.
99  Register GetValueInMiddleOfBlock(MachineBasicBlock *BB,
100                                   bool ExistingValueOnly = false);
101
102  /// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
103  /// which use their value in the corresponding predecessor.  Note that this
104  /// will not work if the use is supposed to be rewritten to a value defined in
105  /// the same block as the use, but above it.  Any 'AddAvailableValue's added
106  /// for the use's block will be considered to be below it.
107  void RewriteUse(MachineOperand &U);
108
109private:
110  // If ExistingValueOnly is true, will not create any new instructions. Used
111  // for debug values, which cannot modify Codegen.
112  Register GetValueAtEndOfBlockInternal(MachineBasicBlock *BB,
113                                        bool ExistingValueOnly = false);
114};
115
116} // end namespace llvm
117
118#endif // LLVM_CODEGEN_MACHINESSAUPDATER_H
119