//===- MemorySSAUpdater.h - Memory SSA Updater-------------------*- 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

//

//===----------------------------------------------------------------------===//

//

// \file

// An automatic updater for MemorySSA that handles arbitrary insertion,

// deletion, and moves.  It performs phi insertion where necessary, and

// automatically updates the MemorySSA IR to be correct.

// While updating loads or removing instructions is often easy enough to not

// need this, updating stores should generally not be attemped outside this

// API.

//

// Basic API usage:

// Create the memory access you want for the instruction (this is mainly so

// we know where it is, without having to duplicate the entire set of create

// functions MemorySSA supports).

// Call insertDef or insertUse depending on whether it's a MemoryUse or a

// MemoryDef.

// That's it.

//

// For moving, first, move the instruction itself using the normal SSA

// instruction moving API, then just call moveBefore, moveAfter,or moveTo with

// the right arguments.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_ANALYSIS_MEMORYSSAUPDATER_H

#define LLVM_ANALYSIS_MEMORYSSAUPDATER_H

#include "llvm/ADT/SmallPtrSet.h"

#include "llvm/ADT/SmallSet.h"

#include "llvm/ADT/SmallVector.h"

#include "llvm/Analysis/LoopInfo.h"

#include "llvm/Analysis/LoopIterator.h"

#include "llvm/Analysis/MemorySSA.h"

#include "llvm/IR/BasicBlock.h"

#include "llvm/IR/CFGDiff.h"

#include "llvm/IR/Dominators.h"

#include "llvm/IR/Module.h"

#include "llvm/IR/OperandTraits.h"

#include "llvm/IR/Type.h"

#include "llvm/IR/Use.h"

#include "llvm/IR/User.h"

#include "llvm/IR/Value.h"

#include "llvm/IR/ValueHandle.h"

#include "llvm/IR/ValueMap.h"

#include "llvm/Pass.h"

#include "llvm/Support/Casting.h"

#include "llvm/Support/ErrorHandling.h"

namespace llvm {

class Function;

class Instruction;

class MemoryAccess;

class LLVMContext;

class raw_ostream;

using ValueToValueMapTy = ValueMap<const Value *, WeakTrackingVH>;

using PhiToDefMap = SmallDenseMap<MemoryPhi *, MemoryAccess *>;

using CFGUpdate = cfg::Update<BasicBlock *>;

using GraphDiffInvBBPair =

    std::pair<const GraphDiff<BasicBlock *> *, Inverse<BasicBlock *>>;

class MemorySSAUpdater {

private:

  MemorySSA *MSSA;

  /// We use WeakVH rather than a costly deletion to deal with dangling pointers.

  /// MemoryPhis are created eagerly and sometimes get zapped shortly afterwards.

  SmallVector<WeakVH, 16> InsertedPHIs;

  SmallPtrSet<BasicBlock *, 8> VisitedBlocks;

  SmallSet<AssertingVH<MemoryPhi>, 8> NonOptPhis;

public:

  MemorySSAUpdater(MemorySSA *MSSA) : MSSA(MSSA) {}

  /// Insert a definition into the MemorySSA IR.  RenameUses will rename any use

  /// below the new def block (and any inserted phis).  RenameUses should be set

  /// to true if the definition may cause new aliases for loads below it.  This

  /// is not the case for hoisting or sinking or other forms of code *movement*.

  /// It *is* the case for straight code insertion.

  /// For example:

  /// store a

  /// if (foo) { }

  /// load a

  ///

  /// Moving the store into the if block, and calling insertDef, does not

  /// require RenameUses.

  /// However, changing it to:

  /// store a

  /// if (foo) { store b }

  /// load a

  /// Where a mayalias b, *does* require RenameUses be set to true.

  void insertDef(MemoryDef *Def, bool RenameUses = false);

  void insertUse(MemoryUse *Use);

  /// Update the MemoryPhi in `To` following an edge deletion between `From` and

  /// `To`. If `To` becomes unreachable, a call to removeBlocks should be made.

  void removeEdge(BasicBlock *From, BasicBlock *To);

  /// Update the MemoryPhi in `To` to have a single incoming edge from `From`,

  /// following a CFG change that replaced multiple edges (switch) with a direct

  /// branch.

  void removeDuplicatePhiEdgesBetween(BasicBlock *From, BasicBlock *To);

  /// Update MemorySSA after a loop was cloned, given the blocks in RPO order,

  /// the exit blocks and a 1:1 mapping of all blocks and instructions

  /// cloned. This involves duplicating all defs and uses in the cloned blocks

  /// Updating phi nodes in exit block successors is done separately.

  void updateForClonedLoop(const LoopBlocksRPO &LoopBlocks,

                           ArrayRef<BasicBlock *> ExitBlocks,

                           const ValueToValueMapTy &VM,

                           bool IgnoreIncomingWithNoClones = false);

  // Block BB was fully or partially cloned into its predecessor P1. Map

  // contains the 1:1 mapping of instructions cloned and VM[BB]=P1.

  void updateForClonedBlockIntoPred(BasicBlock *BB, BasicBlock *P1,

                                    const ValueToValueMapTy &VM);

  /// Update phi nodes in exit block successors following cloning. Exit blocks

  /// that were not cloned don't have additional predecessors added.

  void updateExitBlocksForClonedLoop(ArrayRef<BasicBlock *> ExitBlocks,

                                     const ValueToValueMapTy &VMap,

                                     DominatorTree &DT);

  void updateExitBlocksForClonedLoop(

      ArrayRef<BasicBlock *> ExitBlocks,

      ArrayRef<std::unique_ptr<ValueToValueMapTy>> VMaps, DominatorTree &DT);

  /// Apply CFG updates, analogous with the DT edge updates.

  void applyUpdates(ArrayRef<CFGUpdate> Updates, DominatorTree &DT);

  /// Apply CFG insert updates, analogous with the DT edge updates.

  void applyInsertUpdates(ArrayRef<CFGUpdate> Updates, DominatorTree &DT);

  void moveBefore(MemoryUseOrDef *What, MemoryUseOrDef *Where);

  void moveAfter(MemoryUseOrDef *What, MemoryUseOrDef *Where);

  void moveToPlace(MemoryUseOrDef *What, BasicBlock *BB,

                   MemorySSA::InsertionPlace Where);

  /// `From` block was spliced into `From` and `To`. There is a CFG edge from

  /// `From` to `To`. Move all accesses from `From` to `To` starting at

  /// instruction `Start`. `To` is newly created BB, so empty of

  /// MemorySSA::MemoryAccesses. Edges are already updated, so successors of

  /// `To` with MPhi nodes need to update incoming block.

  /// |------|        |------|

  /// | From |        | From |

  /// |      |        |------|

  /// |      |           ||

  /// |      |   =>      \/

  /// |      |        |------|  <- Start

  /// |      |        |  To  |

  /// |------|        |------|

  void moveAllAfterSpliceBlocks(BasicBlock *From, BasicBlock *To,

                                Instruction *Start);

  /// `From` block was merged into `To`. There is a CFG edge from `To` to

  /// `From`.`To` still branches to `From`, but all instructions were moved and

  /// `From` is now an empty block; `From` is about to be deleted. Move all

  /// accesses from `From` to `To` starting at instruction `Start`. `To` may

  /// have multiple successors, `From` has a single predecessor. `From` may have

  /// successors with MPhi nodes, replace their incoming block with `To`.

  /// |------|        |------|

  /// |  To  |        |  To  |

  /// |------|        |      |

  ///    ||      =>   |      |

  ///    \/           |      |

  /// |------|        |      |  <- Start

  /// | From |        |      |

  /// |------|        |------|

  void moveAllAfterMergeBlocks(BasicBlock *From, BasicBlock *To,

                               Instruction *Start);

  /// A new empty BasicBlock (New) now branches directly to Old. Some of

  /// Old's predecessors (Preds) are now branching to New instead of Old.

  /// If New is the only predecessor, move Old's Phi, if present, to New.

  /// Otherwise, add a new Phi in New with appropriate incoming values, and

  /// update the incoming values in Old's Phi node too, if present.

  void wireOldPredecessorsToNewImmediatePredecessor(

      BasicBlock *Old, BasicBlock *New, ArrayRef<BasicBlock *> Preds,

      bool IdenticalEdgesWereMerged = true);

  // The below are utility functions. Other than creation of accesses to pass

  // to insertDef, and removeAccess to remove accesses, you should generally

  // not attempt to update memoryssa yourself. It is very non-trivial to get

  // the edge cases right, and the above calls already operate in near-optimal

  // time bounds.

  /// Create a MemoryAccess in MemorySSA at a specified point in a block,

  /// with a specified clobbering definition.

  ///

  /// Returns the new MemoryAccess.

  /// This should be called when a memory instruction is created that is being

  /// used to replace an existing memory instruction. It will *not* create PHI

  /// nodes, or verify the clobbering definition. The insertion place is used

  /// solely to determine where in the memoryssa access lists the instruction

  /// will be placed. The caller is expected to keep ordering the same as

  /// instructions.

  /// It will return the new MemoryAccess.

  /// Note: If a MemoryAccess already exists for I, this function will make it

  /// inaccessible and it *must* have removeMemoryAccess called on it.

  MemoryAccess *createMemoryAccessInBB(Instruction *I, MemoryAccess *Definition,

                                       const BasicBlock *BB,

                                       MemorySSA::InsertionPlace Point);

  /// Create a MemoryAccess in MemorySSA before or after an existing

  /// MemoryAccess.

  ///

  /// Returns the new MemoryAccess.

  /// This should be called when a memory instruction is created that is being

  /// used to replace an existing memory instruction. It will *not* create PHI

  /// nodes, or verify the clobbering definition.

  ///

  /// Note: If a MemoryAccess already exists for I, this function will make it

  /// inaccessible and it *must* have removeMemoryAccess called on it.

  MemoryUseOrDef *createMemoryAccessBefore(Instruction *I,

                                           MemoryAccess *Definition,

                                           MemoryUseOrDef *InsertPt);

  MemoryUseOrDef *createMemoryAccessAfter(Instruction *I,

                                          MemoryAccess *Definition,

                                          MemoryAccess *InsertPt);

  /// Remove a MemoryAccess from MemorySSA, including updating all

  /// definitions and uses.

  /// This should be called when a memory instruction that has a MemoryAccess

  /// associated with it is erased from the program.  For example, if a store or

  /// load is simply erased (not replaced), removeMemoryAccess should be called

  /// on the MemoryAccess for that store/load.

  void removeMemoryAccess(MemoryAccess *, bool OptimizePhis = false);

  /// Remove MemoryAccess for a given instruction, if a MemoryAccess exists.

  /// This should be called when an instruction (load/store) is deleted from

  /// the program.

  void removeMemoryAccess(const Instruction *I, bool OptimizePhis = false) {

    if (MemoryAccess *MA = MSSA->getMemoryAccess(I))

      removeMemoryAccess(MA, OptimizePhis);

  }

  /// Remove all MemoryAcceses in a set of BasicBlocks about to be deleted.

  /// Assumption we make here: all uses of deleted defs and phi must either

  /// occur in blocks about to be deleted (thus will be deleted as well), or

  /// they occur in phis that will simply lose an incoming value.

  /// Deleted blocks still have successor info, but their predecessor edges and

  /// Phi nodes may already be updated. Instructions in DeadBlocks should be

  /// deleted after this call.

  void removeBlocks(const SmallPtrSetImpl<BasicBlock *> &DeadBlocks);

  /// Get handle on MemorySSA.

  MemorySSA* getMemorySSA() const { return MSSA; }

private:

  // Move What before Where in the MemorySSA IR.

  template <class WhereType>

  void moveTo(MemoryUseOrDef *What, BasicBlock *BB, WhereType Where);

  // Move all memory accesses from `From` to `To` starting at `Start`.

  // Restrictions apply, see public wrappers of this method.

  void moveAllAccesses(BasicBlock *From, BasicBlock *To, Instruction *Start);

  MemoryAccess *getPreviousDef(MemoryAccess *);

  MemoryAccess *getPreviousDefInBlock(MemoryAccess *);

  MemoryAccess *

  getPreviousDefFromEnd(BasicBlock *,

                        DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> &);

  MemoryAccess *

  getPreviousDefRecursive(BasicBlock *,

                          DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> &);

  MemoryAccess *recursePhi(MemoryAccess *Phi);

  template <class RangeType>

  MemoryAccess *tryRemoveTrivialPhi(MemoryPhi *Phi, RangeType &Operands);

  void fixupDefs(const SmallVectorImpl<WeakVH> &);

  // Clone all uses and defs from BB to NewBB given a 1:1 map of all

  // instructions and blocks cloned, and a map of MemoryPhi : Definition

  // (MemoryAccess Phi or Def). VMap maps old instructions to cloned

  // instructions and old blocks to cloned blocks. MPhiMap, is created in the

  // caller of this private method, and maps existing MemoryPhis to new

  // definitions that new MemoryAccesses must point to. These definitions may

  // not necessarily be MemoryPhis themselves, they may be MemoryDefs. As such,

  // the map is between MemoryPhis and MemoryAccesses, where the MemoryAccesses

  // may be MemoryPhis or MemoryDefs and not MemoryUses.

  void cloneUsesAndDefs(BasicBlock *BB, BasicBlock *NewBB,

                        const ValueToValueMapTy &VMap, PhiToDefMap &MPhiMap);

  template <typename Iter>

  void privateUpdateExitBlocksForClonedLoop(ArrayRef<BasicBlock *> ExitBlocks,

                                            Iter ValuesBegin, Iter ValuesEnd,

                                            DominatorTree &DT);

  void applyInsertUpdates(ArrayRef<CFGUpdate>, DominatorTree &DT,

                          const GraphDiff<BasicBlock *> *GD);

};

} // end namespace llvm

#endif // LLVM_ANALYSIS_MEMORYSSAUPDATER_H