1 //===- MachineSSAUpdater.h - Unstructured SSA Update Tool -------*- C++ -*-===//
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
7 //===----------------------------------------------------------------------===//
9 // This file declares the MachineSSAUpdater class.
11 //===----------------------------------------------------------------------===//
13 #ifndef LLVM_CODEGEN_MACHINESSAUPDATER_H
14 #define LLVM_CODEGEN_MACHINESSAUPDATER_H
16 #include "llvm/CodeGen/Register.h"
20 class MachineBasicBlock;
21 class MachineFunction;
24 class MachineRegisterInfo;
25 class TargetInstrInfo;
26 class TargetRegisterClass;
27 template<typename T> class SmallVectorImpl;
28 template<typename T> class SSAUpdaterTraits;
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.
34 class MachineSSAUpdater {
35 friend class SSAUpdaterTraits<MachineSSAUpdater>;
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;
43 /// VR - Current virtual register whose uses are being updated.
46 /// VRC - Register class of the current virtual register.
47 const TargetRegisterClass *VRC;
49 /// InsertedPHIs - If this is non-null, the MachineSSAUpdater adds all PHI
50 /// nodes that it creates to the vector.
51 SmallVectorImpl<MachineInstr*> *InsertedPHIs;
53 const TargetInstrInfo *TII;
54 MachineRegisterInfo *MRI;
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*> *NewPHI = nullptr);
61 MachineSSAUpdater(const MachineSSAUpdater &) = delete;
62 MachineSSAUpdater &operator=(const MachineSSAUpdater &) = delete;
65 /// Initialize - Reset this object to get ready for a new set of SSA
67 void Initialize(Register V);
69 /// AddAvailableValue - Indicate that a rewritten value is available at the
70 /// end of the specified block with the specified value.
71 void AddAvailableValue(MachineBasicBlock *BB, Register V);
73 /// HasValueForBlock - Return true if the MachineSSAUpdater already has a
74 /// value for the specified block.
75 bool HasValueForBlock(MachineBasicBlock *BB) const;
77 /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
78 /// live at the end of the specified block.
79 Register GetValueAtEndOfBlock(MachineBasicBlock *BB);
81 /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
82 /// is live in the middle of the specified block.
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:
92 /// br Cond, SomeBB, OutBB
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);
101 /// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
102 /// which use their value in the corresponding predecessor. Note that this
103 /// will not work if the use is supposed to be rewritten to a value defined in
104 /// the same block as the use, but above it. Any 'AddAvailableValue's added
105 /// for the use's block will be considered to be below it.
106 void RewriteUse(MachineOperand &U);
109 Register GetValueAtEndOfBlockInternal(MachineBasicBlock *BB);
112 } // end namespace llvm
114 #endif // LLVM_CODEGEN_MACHINESSAUPDATER_H