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//===- 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/MemorySSA.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/IR/ValueMap.h"
#include "llvm/Support/CFGDiff.h"
namespace llvm {
class BasicBlock;
class DominatorTree;
class Instruction;
class LoopBlocksRPO;
template <typename T, unsigned int N> class SmallSetVector;
using ValueToValueMapTy = ValueMap<const Value *, WeakTrackingVH>;
using PhiToDefMap = SmallDenseMap<MemoryPhi *, MemoryAccess *>;
using CFGUpdate = cfg::Update<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, bool RenameUses = false);
/// 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(const BasicBlock *From,
const BasicBlock *To);
/// Update MemorySSA when inserting a unique backedge block for a loop.
void updatePhisWhenInsertingUniqueBackedgeBlock(BasicBlock *LoopHeader,
BasicBlock *LoopPreheader,
BasicBlock *BackedgeBlock);
/// 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. By default, the
/// DT is assumed to be already up to date. If UpdateDTFirst is true, first
/// update the DT with the same updates.
void applyUpdates(ArrayRef<CFGUpdate> Updates, DominatorTree &DT,
bool UpdateDTFirst = false);
/// 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.
///
/// When used by itself, this method will only insert the new MemoryAccess
/// into the access list, but not make any other changes, such as inserting
/// MemoryPHI nodes, or updating users to point to the new MemoryAccess. You
/// must specify a correct Definition in this case.
///
/// Usually, this API is instead combined with insertUse() or insertDef(),
/// which will perform all the necessary MSSA updates. If these APIs are used,
/// then nullptr can be used as Definition, as the correct defining access
/// will be automatically determined.
///
/// 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);
MemoryAccess *createMemoryAccessInBB(Instruction *I, MemoryAccess *Definition,
const BasicBlock *BB,
MemorySSA::InsertionPlace Point,
bool CreationMustSucceed);
/// Create a MemoryAccess in MemorySSA before an existing MemoryAccess.
///
/// See createMemoryAccessInBB() for usage details.
MemoryUseOrDef *createMemoryAccessBefore(Instruction *I,
MemoryAccess *Definition,
MemoryUseOrDef *InsertPt);
/// Create a MemoryAccess in MemorySSA after an existing MemoryAccess.
///
/// See createMemoryAccessInBB() for usage details.
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 SmallSetVector<BasicBlock *, 8> &DeadBlocks);
/// Instruction I will be changed to an unreachable. Remove all accesses in
/// I's block that follow I (inclusive), and update the Phis in the blocks'
/// successors.
void changeToUnreachable(const Instruction *I);
/// 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);
MemoryAccess *tryRemoveTrivialPhi(MemoryPhi *Phi);
template <class RangeType>
MemoryAccess *tryRemoveTrivialPhi(MemoryPhi *Phi, RangeType &Operands);
void tryRemoveTrivialPhis(ArrayRef<WeakVH> UpdatedPHIs);
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.
// If CloneWasSimplified = true, the clone was exact. Otherwise, assume that
// the clone involved simplifications that may have: (1) turned a MemoryUse
// into an instruction that MemorySSA has no representation for, or (2) turned
// a MemoryDef into a MemoryUse or an instruction that MemorySSA has no
// representation for. No other cases are supported.
void cloneUsesAndDefs(BasicBlock *BB, BasicBlock *NewBB,
const ValueToValueMapTy &VMap, PhiToDefMap &MPhiMap,
bool CloneWasSimplified = false);
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
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