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 //===- MachineSSAUpdater.h - Unstructured SSA Update Tool -------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file declares the MachineSSAUpdater class.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CODEGEN_MACHINESSAUPDATER_H
 #define LLVM_CODEGEN_MACHINESSAUPDATER_H
 
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/Register.h"
 
 namespace llvm {
 
 class MachineBasicBlock;
 class MachineFunction;
 class MachineInstr;
 class MachineOperand;
 class MachineRegisterInfo;
 class TargetInstrInfo;
 class TargetRegisterClass;
 template<typename T> class SmallVectorImpl;
 template<typename T> class SSAUpdaterTraits;
 
 /// MachineSSAUpdater - This class updates SSA form for a set of virtual
 /// registers defined in multiple blocks.  This is used when code duplication
 /// or another unstructured transformation wants to rewrite a set of uses of one
 /// vreg with uses of a set of vregs.
 class MachineSSAUpdater {
   friend class SSAUpdaterTraits<MachineSSAUpdater>;
 
 private:
   /// AvailableVals - This keeps track of which value to use on a per-block
   /// basis.  When we insert PHI nodes, we keep track of them here.
   //typedef DenseMap<MachineBasicBlock*, Register> AvailableValsTy;
   void *AV = nullptr;
 
   /// Register class or bank and LLT of current virtual register.
   MachineRegisterInfo::VRegAttrs RegAttrs;
 
   /// InsertedPHIs - If this is non-null, the MachineSSAUpdater adds all PHI
   /// nodes that it creates to the vector.
   SmallVectorImpl<MachineInstr*> *InsertedPHIs;
 
   const TargetInstrInfo *TII = nullptr;
   MachineRegisterInfo *MRI = nullptr;
 
 public:
   /// MachineSSAUpdater constructor.  If InsertedPHIs is specified, it will be
   /// filled in with all PHI Nodes created by rewriting.
   explicit MachineSSAUpdater(MachineFunction &MF,
                         SmallVectorImpl<MachineInstr*> *NewPHI = nullptr);
   MachineSSAUpdater(const MachineSSAUpdater &) = delete;
   MachineSSAUpdater &operator=(const MachineSSAUpdater &) = delete;
   ~MachineSSAUpdater();
 
   /// Initialize - Reset this object to get ready for a new set of SSA
   /// updates.
   void Initialize(Register V);
 
   /// AddAvailableValue - Indicate that a rewritten value is available at the
   /// end of the specified block with the specified value.
   void AddAvailableValue(MachineBasicBlock *BB, Register V);
 
   /// HasValueForBlock - Return true if the MachineSSAUpdater already has a
   /// value for the specified block.
   bool HasValueForBlock(MachineBasicBlock *BB) const;
 
   /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
   /// live at the end of the specified block.
   Register GetValueAtEndOfBlock(MachineBasicBlock *BB);
 
   /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
   /// is live in the middle of the specified block. If ExistingValueOnly is
   /// true then this will only return an existing value or $noreg; otherwise new
   /// instructions may be inserted to materialize a value.
   ///
   /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
   /// important case: if there is a definition of the rewritten value after the
   /// 'use' in BB.  Consider code like this:
   ///
   ///      X1 = ...
   ///   SomeBB:
   ///      use(X)
   ///      X2 = ...
   ///      br Cond, SomeBB, OutBB
   ///
   /// In this case, there are two values (X1 and X2) added to the AvailableVals
   /// set by the client of the rewriter, and those values are both live out of
   /// their respective blocks.  However, the use of X happens in the *middle* of
   /// a block.  Because of this, we need to insert a new PHI node in SomeBB to
   /// merge the appropriate values, and this value isn't live out of the block.
   Register GetValueInMiddleOfBlock(MachineBasicBlock *BB,
                                    bool ExistingValueOnly = false);
 
   /// RewriteUse - Rewrite a use of the symbolic value.  This handles PHI nodes,
   /// which use their value in the corresponding predecessor.  Note that this
   /// will not work if the use is supposed to be rewritten to a value defined in
   /// the same block as the use, but above it.  Any 'AddAvailableValue's added
   /// for the use's block will be considered to be below it.
   void RewriteUse(MachineOperand &U);
 
 private:
   // If ExistingValueOnly is true, will not create any new instructions. Used
   // for debug values, which cannot modify Codegen.
   Register GetValueAtEndOfBlockInternal(MachineBasicBlock *BB,
                                         bool ExistingValueOnly = false);
 };
 
 } // end namespace llvm
 
 #endif // LLVM_CODEGEN_MACHINESSAUPDATER_H

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