Region.h

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//===- Region.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
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_SANDBOXIR_REGION_H
#define LLVM_SANDBOXIR_REGION_H
 
#include "llvm/Support/Compiler.h"
#include <memory>
 
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/SandboxIR/Instruction.h"
#include "llvm/Support/raw_ostream.h"
 
namespace llvm::sandboxir {
 
class Region;
 
class ScoreBoard {
  const Region &Rgn;
  TargetTransformInfo &TTI;
  constexpr static TTI::TargetCostKind CostKind = TTI::TCK_RecipThroughput;
  /// The cost of all instructions added to the region.
  InstructionCost AfterCost = 0;
  /// The cost of all instructions that got removed and replaced by new ones.
  InstructionCost BeforeCost = 0;
  /// Helper for both add() and remove(). \Returns the TTI cost of \p I.
  LLVM_ABI InstructionCost getCost(Instruction *I) const;
  /// No need to allow copies.
  ScoreBoard(const ScoreBoard &) = delete;
  const ScoreBoard &operator=(const ScoreBoard &) = delete;
 
public:
  ScoreBoard(Region &Rgn, TargetTransformInfo &TTI) : Rgn(Rgn), TTI(TTI) {}
  /// Mark \p I as a newly added instruction to the region.
  void add(Instruction *I) { AfterCost += getCost(I); }
  /// Mark \p I as a deleted instruction from the region.
  LLVM_ABI void remove(Instruction *I);
  /// \Returns the cost of the newly added instructions.
  InstructionCost getAfterCost() const { return AfterCost; }
  /// \Returns the cost of the Removed instructions.
  InstructionCost getBeforeCost() const { return BeforeCost; }
 
#ifndef NDEBUG
  void dump(raw_ostream &OS) const {
    OS << "BeforeCost: " << BeforeCost << "\n";
    OS << "AfterCost:  " << AfterCost << "\n";
  }
  LLVM_DUMP_METHOD void dump() const;
#endif // NDEBUG
};
 
/// The main job of the Region is to point to new instructions generated by
/// vectorization passes. It is the unit that RegionPasses operate on with their
/// runOnRegion() function.
///
/// The region allows us to stack transformations horizontally, meaning that
/// each transformation operates on a single region and the resulting region is
/// the input to the next transformation, as opposed to vertically, which is the
/// common way of applying a transformation across the whole function. This
/// enables us to check for profitability and decide whether we accept or
/// rollback at a region granularity, which is much better than doing this at
/// the function level.
///
//  Traditional approach: transformations applied vertically for the whole
//  function
//    F
//  +----+
//  |    |
//  |    |
//  |    | -> Transform1 ->  ... -> TransformN -> Check Cost
//  |    |
//  |    |
//  +----+
//
//  Region-based approach: transformations applied horizontally, for each Region
//    F
//  +----+
//  |Rgn1| -> Transform1 ->  ... -> TransformN -> Check Cost
//  |    |
//  |Rgn2| -> Transform1 ->  ... -> TransformN -> Check Cost
//  |    |
//  |Rgn3| -> Transform1 ->  ... -> TransformN -> Check Cost
//  +----+
//
// The region can also hold an ordered sequence of "auxiliary" instructions.
// This can be used to pass auxiliary information across region passes, like for
// example the initial seed slice used by the bottom-up vectorizer.
 
class Region {
  /// All the instructions in the Region. Only new instructions generated during
  /// vectorization are part of the Region.
  SetVector<Instruction *> Insts;
  /// An auxiliary sequence of Instruction-Index pairs.
  SmallVector<Instruction *> Aux;
 
  /// MDNode that we'll use to mark instructions as being part of the region.
  MDNode *RegionMDN;
  static constexpr const char *MDKind = "sandboxvec";
  static constexpr const char *RegionStr = "sandboxregion";
  static constexpr const char *AuxMDKind = "sandboxaux";
 
  Context &Ctx;
  /// Keeps track of cost of instructions added and removed.
  ScoreBoard Scoreboard;
 
  /// ID (for later deregistration) of the "create instruction" callback.
  Context::CallbackID CreateInstCB;
  /// ID (for later deregistration) of the "erase instruction" callback.
  Context::CallbackID EraseInstCB;
 
  /// Adds \p I to the set but also don't track the instruction's score if \p
  /// IgnoreCost is true. Only to be used when adding an instruction to the
  /// auxiliary vector.
  /// NOTE: When an instruction is added to the region we track it cost in the
  /// scoreboard, which currently resides in the region class. However, when we
  /// add an instruction to the auxiliary vector it does get tagged as being a
  /// member of the region (for ownership reasons), but its cost does not get
  /// counted because the instruction hasn't been added in the "normal" way.
  LLVM_ABI void addImpl(Instruction *I, bool IgnoreCost);
  /// Adds I to the set. This is the main API for adding an instruction to the
  /// region.
  void add(Instruction *I) { addImpl(I, /*IgnoreCost=*/false); }
  /// Removes I from the set.
  LLVM_ABI void remove(Instruction *I);
  friend class Context; // The callbacks need to call add() and remove().
  friend class RegionInternalsAttorney; // For unit tests.
  friend class RegionsFromBBs;          // For add().
 
  /// Set \p I as the \p Idx'th element in the auxiliary vector.
  /// NOTE: This is for internal use, it does not set the metadata.
  void setAux(unsigned Idx, Instruction *I);
  /// Helper for dropping Aux metadata for \p I.
  void dropAuxMetadata(Instruction *I);
  /// Remove instruction \p I from Aux and drop metadata.
  void removeFromAux(Instruction *I);
 
public:
  LLVM_ABI Region(Context &Ctx, TargetTransformInfo &TTI);
  LLVM_ABI ~Region();
 
  Context &getContext() const { return Ctx; }
  /// Returns true if I is in the Region.
  bool contains(Instruction *I) const { return Insts.contains(I); }
  /// Returns true if the Region has no instructions.
  bool empty() const { return Insts.empty(); }
  /// Set the auxiliary vector.
  LLVM_ABI void setAux(ArrayRef<Instruction *> Aux);
  /// \Returns the auxiliary vector.
  const SmallVector<Instruction *> &getAux() const { return Aux; }
  /// Clears all auxiliary data.
  LLVM_ABI void clearAux();
 
  using iterator = decltype(Insts.begin());
  iterator begin() { return Insts.begin(); }
  iterator end() { return Insts.end(); }
  iterator_range<iterator> insts() { return make_range(begin(), end()); }
 
  LLVM_ABI static SmallVector<std::unique_ptr<Region>>
  createRegionsFromMD(Function &F, TargetTransformInfo &TTI);
  /// \Returns the ScoreBoard data structure that keeps track of instr costs.
  const ScoreBoard &getScoreboard() const { return Scoreboard; }
 
#ifndef NDEBUG
  /// This is an expensive check, meant for testing.
  bool operator==(const Region &Other) const;
  bool operator!=(const Region &other) const { return !(*this == other); }
 
  void dump(raw_ostream &OS) const;
  void dump() const;
  friend raw_ostream &operator<<(raw_ostream &OS, const Region &Rgn) {
    Rgn.dump(OS);
    return OS;
  }
#endif
};
 
/// A helper client-attorney class for unit tests.
class RegionInternalsAttorney {
public:
  static void add(Region &Rgn, Instruction *I) { Rgn.add(I); }
  static void remove(Region &Rgn, Instruction *I) { Rgn.remove(I); }
};
 
} // namespace llvm::sandboxir
 
#endif // LLVM_SANDBOXIR_REGION_H