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 namespace llvm { 17 18 class MachineBasicBlock; 19 class MachineFunction; 20 class MachineInstr; 21 class MachineOperand; 22 class MachineRegisterInfo; 23 class TargetInstrInfo; 24 class TargetRegisterClass; 25 template<typename T> class SmallVectorImpl; 26 template<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. 32 class MachineSSAUpdater { 33 friend class SSAUpdaterTraits<MachineSSAUpdater>; 34 35 private: 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 54 public: 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); 105 106 private: 107 unsigned GetValueAtEndOfBlockInternal(MachineBasicBlock *BB); 108 }; 109 110 } // end namespace llvm 111 112 #endif // LLVM_CODEGEN_MACHINESSAUPDATER_H 113