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#include "llvm/Support/Allocator.h"
18#include "llvm/Support/Compiler.h"
19
20namespace llvm {
21  class MachineBasicBlock;
22  class MachineFunction;
23  class MachineInstr;
24  class MachineOperand;
25  class MachineRegisterInfo;
26  class TargetInstrInfo;
27  class TargetRegisterClass;
28  template<typename T> class SmallVectorImpl;
29  template<typename T> class SSAUpdaterTraits;
30
31/// MachineSSAUpdater - This class updates SSA form for a set of virtual
32/// registers defined in multiple blocks.  This is used when code duplication
33/// or another unstructured transformation wants to rewrite a set of uses of one
34/// vreg with uses of a set of vregs.
35class MachineSSAUpdater {
36  friend class SSAUpdaterTraits<MachineSSAUpdater>;
37
38private:
39  /// AvailableVals - This keeps track of which value to use on a per-block
40  /// basis.  When we insert PHI nodes, we keep track of them here.
41  //typedef DenseMap<MachineBasicBlock*, unsigned > AvailableValsTy;
42  void *AV;
43
44  /// VR - Current virtual register whose uses are being updated.
45  unsigned VR;
46
47  /// VRC - Register class of the current virtual register.
48  const TargetRegisterClass *VRC;
49
50  /// InsertedPHIs - If this is non-null, the MachineSSAUpdater adds all PHI
51  /// nodes that it creates to the vector.
52  SmallVectorImpl<MachineInstr*> *InsertedPHIs;
53
54  const TargetInstrInfo *TII;
55  MachineRegisterInfo *MRI;
56public:
57  /// MachineSSAUpdater constructor.  If InsertedPHIs is specified, it will be
58  /// filled in with all PHI Nodes created by rewriting.
59  explicit MachineSSAUpdater(MachineFunction &MF,
60                        SmallVectorImpl<MachineInstr*> *InsertedPHIs = nullptr);
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  ///
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  void operator=(const MachineSSAUpdater&) LLVM_DELETED_FUNCTION;
111  MachineSSAUpdater(const MachineSSAUpdater&) LLVM_DELETED_FUNCTION;
112};
113
114} // End llvm namespace
115
116#endif
117