include/llvm/CodeGen/MachineSSAUpdater.h

   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