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//===------ ZoneAlgo.h ------------------------------------------*- 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

//

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

//

// Derive information about array elements between statements ("Zones").

//

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

#ifndef POLLY_ZONEALGO_H

#define POLLY_ZONEALGO_H

#include "llvm/ADT/DenseMap.h"

#include "llvm/ADT/DenseSet.h"

#include "llvm/ADT/SmallPtrSet.h"

#include "isl/isl-noexceptions.h"

#include <memory>

namespace llvm {

class Value;

class LoopInfo;

class Loop;

class PHINode;

class raw_ostream;

} // namespace llvm

namespace polly {

class Scop;

class ScopStmt;

class MemoryAccess;

class ScopArrayInfo;

/// Return only the mappings that map to known values.

///

/// @param UMap { [] -> ValInst[] }

///

/// @return { [] -> ValInst[] }

isl::union_map filterKnownValInst(const isl::union_map &UMap);

/// Base class for algorithms based on zones, like DeLICM.

class ZoneAlgorithm {

protected:

  /// The name of the pass this is used from. Used for optimization remarks.

  const char *PassName;

  /// Hold a reference to the isl_ctx to avoid it being freed before we released

  /// all of the isl objects.

  ///

  /// This must be declared before any other member that holds an isl object.

  /// This guarantees that the shared_ptr and its isl_ctx is destructed last,

  /// after all other members free'd the isl objects they were holding.

  std::shared_ptr<isl_ctx> IslCtx;

  /// Cached reaching definitions for each ScopStmt.

  ///

  /// Use getScalarReachingDefinition() to get its contents.

  llvm::DenseMap<ScopStmt *, isl::map> ScalarReachDefZone;

  /// The analyzed Scop.

  Scop *S;

  /// LoopInfo analysis used to determine whether values are synthesizable.

  llvm::LoopInfo *LI;

  /// Parameter space that does not need realignment.

  isl::space ParamSpace;

  /// Space the schedule maps to.

  isl::space ScatterSpace;

  /// Cached version of the schedule and domains.

  isl::union_map Schedule;

  /// Combined access relations of all MemoryKind::Array READ accesses.

  /// { DomainRead[] -> Element[] }

  isl::union_map AllReads;

  /// The loaded values (llvm::LoadInst) of all reads.

  /// { [Element[] -> DomainRead[]] -> ValInst[] }

  isl::union_map AllReadValInst;

  /// Combined access relations of all MemoryKind::Array, MAY_WRITE accesses.

  /// { DomainMayWrite[] -> Element[] }

  isl::union_map AllMayWrites;

  /// Combined access relations of all MemoryKind::Array, MUST_WRITE accesses.

  /// { DomainMustWrite[] -> Element[] }

  isl::union_map AllMustWrites;

  /// Combined access relations of all MK_Array write accesses (union of

  /// AllMayWrites and AllMustWrites).

  /// { DomainWrite[] -> Element[] }

  isl::union_map AllWrites;

  /// The value instances written to array elements of all write accesses.

  /// { [Element[] -> DomainWrite[]] -> ValInst[] }

  isl::union_map AllWriteValInst;

  /// All reaching definitions for  MemoryKind::Array writes.

  /// { [Element[] -> Zone[]] -> DomainWrite[] }

  isl::union_map WriteReachDefZone;

  /// Map llvm::Values to an isl identifier.

  /// Used with -polly-use-llvm-names=false as an alternative method to get

  /// unique ids that do not depend on pointer values.

  llvm::DenseMap<llvm::Value *, isl::id> ValueIds;

  /// Set of array elements that can be reliably used for zone analysis.

  /// { Element[] }

  isl::union_set CompatibleElts;

  /// List of PHIs that may transitively refer to themselves.

  ///

  /// Computing them would require a polyhedral transitive closure operation,

  /// for which isl may only return an approximation. For correctness, we always

  /// require an exact result. Hence, we exclude such PHIs.

  llvm::SmallPtrSet<llvm::PHINode *, 4> RecursivePHIs;

  /// PHIs that have been computed.

  ///

  /// Computed PHIs are replaced by their incoming values using #NormalizeMap.

  llvm::DenseSet<llvm::PHINode *> ComputedPHIs;

  /// For computed PHIs, contains the ValInst they stand for.

  ///

  /// To show an example, assume the following PHINode:

  ///

  ///   Stmt:

  ///     %phi = phi double [%val1, %bb1], [%val2, %bb2]

  ///

  /// It's ValInst is:

  ///

  ///   { [Stmt[i] -> phi[]] }

  ///

  /// The value %phi will be either %val1 or %val2, depending on whether in

  /// iteration i %bb1 or %bb2 has been executed before. In SCoPs, this can be

  /// determined at compile-time, and the result stored in #NormalizeMap. For

  /// the previous example, it could be:

  ///

  ///   { [Stmt[i] -> phi[]] -> [Stmt[0] -> val1[]];

  ///     [Stmt[i] -> phi[]] -> [Stmt[i] -> val2[]] : i > 0 }

  ///

  /// Only ValInsts in #ComputedPHIs are present in this map. Other values are

  /// assumed to represent themselves. This is to avoid adding lots of identity

  /// entries to this map.

  ///

  /// { PHIValInst[] -> IncomingValInst[] }

  isl::union_map NormalizeMap;

  /// Cache for computePerPHI(const ScopArrayInfo *)

  llvm::SmallDenseMap<llvm::PHINode *, isl::union_map> PerPHIMaps;

  /// A cache for getDefToTarget().

  llvm::DenseMap<std::pair<ScopStmt *, ScopStmt *>, isl::map> DefToTargetCache;

  /// Prepare the object before computing the zones of @p S.

  ///

  /// @param PassName Name of the pass using this analysis.

  /// @param S        The SCoP to process.

  /// @param LI       LoopInfo analysis used to determine synthesizable values.

  ZoneAlgorithm(const char *PassName, Scop *S, llvm::LoopInfo *LI);

private:

  /// Find the array elements that violate the zone analysis assumptions.

  ///

  /// What violates our assumptions:

  /// - A load after a write of the same location; we assume that all reads

  ///   occur before the writes.

  /// - Two writes to the same location; we cannot model the order in which

  ///   these occur.

  ///

  /// Scalar reads implicitly always occur before other accesses therefore never

  /// violate the first condition. There is also at most one write to a scalar,

  /// satisfying the second condition.

  ///

  /// @param Stmt                  The statement to be analyzed.

  /// @param[out] IncompatibleElts Receives the elements that are not

  ///                              zone-analysis compatible.

  /// @param[out]                  AllElts receives all encountered elements.

  void collectIncompatibleElts(ScopStmt *Stmt, isl::union_set &IncompatibleElts,

                               isl::union_set &AllElts);

  void addArrayReadAccess(MemoryAccess *MA);

  /// Return the ValInst write by a (must-)write access. Returns the 'unknown'

  /// ValInst if there is no single ValInst[] the array element written to will

  /// have.

  ///

  /// @return { ValInst[] }

  isl::union_map getWrittenValue(MemoryAccess *MA, isl::map AccRel);

  void addArrayWriteAccess(MemoryAccess *MA);

  /// For an llvm::Value defined in @p DefStmt, compute the RAW dependency for a

  /// use in every instance of @p UseStmt.

  ///

  /// @param UseStmt Statement a scalar is used in.

  /// @param DefStmt Statement a scalar is defined in.

  ///

  /// @return { DomainUse[] -> DomainDef[] }

  isl::map computeUseToDefFlowDependency(ScopStmt *UseStmt, ScopStmt *DefStmt);

protected:

  isl::union_set makeEmptyUnionSet() const;

  isl::union_map makeEmptyUnionMap() const;

  /// For each 'execution' of a PHINode, get the incoming block that was

  /// executed before.

  ///

  /// For each PHI instance we can directly determine which was the incoming

  /// block, and hence derive which value the PHI has.

  ///

  /// @param SAI The ScopArrayInfo representing the PHI's storage.

  ///

  /// @return { DomainPHIRead[] -> DomainPHIWrite[] }

  isl::union_map computePerPHI(const polly::ScopArrayInfo *SAI);

  /// Find the array elements that can be used for zone analysis.

  void collectCompatibleElts();

  /// Get the schedule for @p Stmt.

  ///

  /// The domain of the result is as narrow as possible.

  isl::map getScatterFor(ScopStmt *Stmt) const;

  /// Get the schedule of @p MA's parent statement.

  isl::map getScatterFor(MemoryAccess *MA) const;

  /// Get the schedule for the statement instances of @p Domain.

  isl::union_map getScatterFor(isl::union_set Domain) const;

  /// Get the schedule for the statement instances of @p Domain.

  isl::map getScatterFor(isl::set Domain) const;

  /// Get the domain of @p Stmt.

  isl::set getDomainFor(ScopStmt *Stmt) const;

  /// Get the domain @p MA's parent statement.

  isl::set getDomainFor(MemoryAccess *MA) const;

  /// Get the access relation of @p MA.

  ///

  /// The domain of the result is as narrow as possible.

  isl::map getAccessRelationFor(MemoryAccess *MA) const;

  /// Get a domain translation map from a (scalar) definition to the statement

  /// where the definition is being moved to.

  ///

  /// @p TargetStmt can also be seen at an llvm::Use of an llvm::Value in

  /// @p DefStmt. In addition, we allow transitive uses:

  ///

  /// DefStmt -> MiddleStmt -> TargetStmt

  ///

  /// where an operand tree of instructions in DefStmt and MiddleStmt are to be

  /// moved to TargetStmt. To be generally correct, we also need to know all the

  /// intermediate statements. However, we make use of the fact that

  /// ForwardOpTree currently does not support a move from a loop body across

  /// its header such that only the first definition and the target statement

  /// are relevant.

  ///

  /// @param DefStmt    Statement from where a definition might be moved from.

  /// @param TargetStmt Statement where the definition is potentially being

  ///                   moved to (should contain a use of that definition).

  ///

  /// @return { DomainDef[] -> DomainTarget[] }

  isl::map getDefToTarget(ScopStmt *DefStmt, ScopStmt *TargetStmt);

  /// Get the reaching definition of a scalar defined in @p Stmt.

  ///

  /// Note that this does not depend on the llvm::Instruction, only on the

  /// statement it is defined in. Therefore the same computation can be reused.

  ///

  /// @param Stmt The statement in which a scalar is defined.

  ///

  /// @return { Scatter[] -> DomainDef[] }

  isl::map getScalarReachingDefinition(ScopStmt *Stmt);

  /// Get the reaching definition of a scalar defined in @p DefDomain.

  ///

  /// @param DomainDef { DomainDef[] }

  ///              The write statements to get the reaching definition for.

  ///

  /// @return { Scatter[] -> DomainDef[] }

  isl::map getScalarReachingDefinition(isl::set DomainDef);

  /// Create a statement-to-unknown value mapping.

  ///

  /// @param Stmt The statement whose instances are mapped to unknown.

  ///

  /// @return { Domain[] -> ValInst[] }

  isl::map makeUnknownForDomain(ScopStmt *Stmt) const;

  /// Create an isl_id that represents @p V.

  isl::id makeValueId(llvm::Value *V);

  /// Create the space for an llvm::Value that is available everywhere.

  isl::space makeValueSpace(llvm::Value *V);

  /// Create a set with the llvm::Value @p V which is available everywhere.

  isl::set makeValueSet(llvm::Value *V);

  /// Create a mapping from a statement instance to the instance of an

  /// llvm::Value that can be used in there.

  ///

  /// Although LLVM IR uses single static assignment, llvm::Values can have

  /// different contents in loops, when they get redefined in the last

  /// iteration. This function tries to get the statement instance of the

  /// previous definition, relative to a user.

  ///

  /// Example:

  /// for (int i = 0; i < N; i += 1) {

  /// DEF:

  ///    int v = A[i];

  /// USE:

  ///    use(v);

  ///  }

  ///

  /// The value instance used by statement instance USE[i] is DEF[i]. Hence,

  /// makeValInst returns:

  ///

  /// { USE[i] -> [DEF[i] -> v[]] : 0 <= i < N }

  ///

  /// @param Val       The value to get the instance of.

  /// @param UserStmt  The statement that uses @p Val. Can be nullptr.

  /// @param Scope     Loop the using instruction resides in.

  /// @param IsCertain Pass true if the definition of @p Val is a

  ///                  MUST_WRITE or false if the write is conditional.

  ///

  /// @return { DomainUse[] -> ValInst[] }

  isl::map makeValInst(llvm::Value *Val, ScopStmt *UserStmt, llvm::Loop *Scope,

                       bool IsCertain = true);

  /// Create and normalize a ValInst.

  ///

  /// @see makeValInst

  /// @see normalizeValInst

  /// @see #NormalizedPHI

  isl::union_map makeNormalizedValInst(llvm::Value *Val, ScopStmt *UserStmt,

                                       llvm::Loop *Scope,

                                       bool IsCertain = true);

  /// Return whether @p MA can be used for transformations (e.g. OpTree load

  /// forwarding, DeLICM mapping).

  bool isCompatibleAccess(MemoryAccess *MA);

  /// Compute the different zones.

  void computeCommon();

  ///  Compute the normalization map that replaces PHIs by their incoming

  ///  values.

  ///

  /// @see #NormalizeMap

  void computeNormalizedPHIs();

  /// Print the current state of all MemoryAccesses to @p.

  void printAccesses(llvm::raw_ostream &OS, int Indent = 0) const;

  /// Is @p MA a PHI READ access that can be normalized?

  ///

  /// @see #NormalizeMap

  bool isNormalizable(MemoryAccess *MA);

  /// @{

  /// Determine whether the argument does not map to any computed PHI. Those

  /// should have been replaced by their incoming values.

  ///

  /// @see #NormalizedPHI

  isl::boolean isNormalized(isl::map Map);

  isl::boolean isNormalized(isl::union_map Map);

  /// @}

public:

  /// Return the SCoP this object is analyzing.

  Scop *getScop() const { return S; }

  /// A reaching definition zone is known to have the definition's written value

  /// if the definition is a MUST_WRITE.

  ///

  /// @return { [Element[] -> Zone[]] -> ValInst[] }

  isl::union_map computeKnownFromMustWrites() const;

  /// A reaching definition zone is known to be the same value as any load that

  /// reads from that array element in that period.

  ///

  /// @return { [Element[] -> Zone[]] -> ValInst[] }

  isl::union_map computeKnownFromLoad() const;

  /// Compute which value an array element stores at every instant.

  ///

  /// @param FromWrite Use stores as source of information.

  /// @param FromRead  Use loads as source of information.

  ///

  /// @return { [Element[] -> Zone[]] -> ValInst[] }

  isl::union_map computeKnown(bool FromWrite, bool FromRead) const;

};

/// Create a domain-to-unknown value mapping.

///

/// Value instances that do not represent a specific value are represented by an

/// unnamed tuple of 0 dimensions. Its meaning depends on the context. It can

/// either mean a specific but unknown value which cannot be represented by

/// other means. It conflicts with itself because those two unknown ValInsts may

/// have different concrete values at runtime.

///

/// The other meaning is an arbitrary or wildcard value that can be chosen

/// freely, like LLVM's undef. If matched with an unknown ValInst, there is no

/// conflict.

///

/// @param Domain { Domain[] }

///

/// @return { Domain[] -> ValInst[] }

isl::union_map makeUnknownForDomain(isl::union_set Domain);

} // namespace polly

#endif /* POLLY_ZONEALGO_H */