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 18 namespace llvm { 19 20 class MachineBasicBlock; 21 class MachineFunction; 22 class MachineInstr; 23 class MachineOperand; 24 class MachineRegisterInfo; 25 class TargetInstrInfo; 26 class TargetRegisterClass; 27 template<typename T> class SmallVectorImpl; 28 template<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. 34 class MachineSSAUpdater { 35 friend class SSAUpdaterTraits<MachineSSAUpdater>; 36 37 private: 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 /// VR - Current virtual register whose uses are being updated. 44 Register VR; 45 46 /// VRC - Register class of the current virtual register. 47 const TargetRegisterClass *VRC; 48 49 /// InsertedPHIs - If this is non-null, the MachineSSAUpdater adds all PHI 50 /// nodes that it creates to the vector. 51 SmallVectorImpl<MachineInstr*> *InsertedPHIs; 52 53 const TargetInstrInfo *TII; 54 MachineRegisterInfo *MRI; 55 56 public: 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; 63 ~MachineSSAUpdater(); 64 65 /// Initialize - Reset this object to get ready for a new set of SSA 66 /// updates. 67 void Initialize(Register V); 68 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); 72 73 /// HasValueForBlock - Return true if the MachineSSAUpdater already has a 74 /// value for the specified block. 75 bool HasValueForBlock(MachineBasicBlock *BB) const; 76 77 /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is 78 /// live at the end of the specified block. 79 Register GetValueAtEndOfBlock(MachineBasicBlock *BB); 80 81 /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that 82 /// is live in the middle of the specified block. 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); 100 101 /// 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); 107 108 private: 109 Register GetValueAtEndOfBlockInternal(MachineBasicBlock *BB); 110 }; 111 112 } // end namespace llvm 113 114 #endif // LLVM_CODEGEN_MACHINESSAUPDATER_H 115