Coverage Report

Created: 2019-02-15 18:59

/Users/buildslave/jenkins/workspace/clang-stage2-coverage-R/llvm/include/llvm/Analysis/DependenceAnalysis.h
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//===-- llvm/Analysis/DependenceAnalysis.h -------------------- -*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// DependenceAnalysis is an LLVM pass that analyses dependences between memory
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// accesses. Currently, it is an implementation of the approach described in
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//
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//            Practical Dependence Testing
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//            Goff, Kennedy, Tseng
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//            PLDI 1991
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//
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// There's a single entry point that analyzes the dependence between a pair
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// of memory references in a function, returning either NULL, for no dependence,
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// or a more-or-less detailed description of the dependence between them.
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//
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// This pass exists to support the DependenceGraph pass. There are two separate
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// passes because there's a useful separation of concerns. A dependence exists
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// if two conditions are met:
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//
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//    1) Two instructions reference the same memory location, and
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//    2) There is a flow of control leading from one instruction to the other.
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//
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// DependenceAnalysis attacks the first condition; DependenceGraph will attack
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// the second (it's not yet ready).
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//
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// Please note that this is work in progress and the interface is subject to
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// change.
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//
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// Plausible changes:
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//    Return a set of more precise dependences instead of just one dependence
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//    summarizing all.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_DEPENDENCEANALYSIS_H
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#define LLVM_ANALYSIS_DEPENDENCEANALYSIS_H
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#include "llvm/ADT/SmallBitVector.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/Pass.h"
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namespace llvm {
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template <typename T> class ArrayRef;
49
  class Loop;
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  class LoopInfo;
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  class ScalarEvolution;
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  class SCEV;
53
  class SCEVConstant;
54
  class raw_ostream;
55
56
  /// Dependence - This class represents a dependence between two memory
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  /// memory references in a function. It contains minimal information and
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  /// is used in the very common situation where the compiler is unable to
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  /// determine anything beyond the existence of a dependence; that is, it
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  /// represents a confused dependence (see also FullDependence). In most
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  /// cases (for output, flow, and anti dependences), the dependence implies
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  /// an ordering, where the source must precede the destination; in contrast,
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  /// input dependences are unordered.
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  ///
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  /// When a dependence graph is built, each Dependence will be a member of
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  /// the set of predecessor edges for its destination instruction and a set
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  /// if successor edges for its source instruction. These sets are represented
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  /// as singly-linked lists, with the "next" fields stored in the dependence
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  /// itelf.
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  class Dependence {
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  protected:
72
670
    Dependence(Dependence &&) = default;
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    Dependence &operator=(Dependence &&) = default;
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  public:
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    Dependence(Instruction *Source,
77
               Instruction *Destination) :
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      Src(Source),
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      Dst(Destination),
80
      NextPredecessor(nullptr),
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2.52k
      NextSuccessor(nullptr) {}
82
3.19k
    virtual ~Dependence() {}
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    /// Dependence::DVEntry - Each level in the distance/direction vector
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    /// has a direction (or perhaps a union of several directions), and
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    /// perhaps a distance.
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    struct DVEntry {
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      enum { NONE = 0,
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             LT = 1,
90
             EQ = 2,
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             LE = 3,
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             GT = 4,
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             NE = 5,
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             GE = 6,
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             ALL = 7 };
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      unsigned char Direction : 3; // Init to ALL, then refine.
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      bool Scalar    : 1; // Init to true.
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      bool PeelFirst : 1; // Peeling the first iteration will break dependence.
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      bool PeelLast  : 1; // Peeling the last iteration will break the dependence.
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      bool Splitable : 1; // Splitting the loop will break dependence.
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      const SCEV *Distance; // NULL implies no distance available.
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      DVEntry() : Direction(ALL), Scalar(true), PeelFirst(false),
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2.41k
                  PeelLast(false), Splitable(false), Distance(nullptr) { }
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    };
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    /// getSrc - Returns the source instruction for this dependence.
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    ///
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6
    Instruction *getSrc() const { return Src; }
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    /// getDst - Returns the destination instruction for this dependence.
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    ///
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6
    Instruction *getDst() const { return Dst; }
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    /// isInput - Returns true if this is an input dependence.
115
    ///
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    bool isInput() const;
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    /// isOutput - Returns true if this is an output dependence.
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    ///
120
    bool isOutput() const;
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    /// isFlow - Returns true if this is a flow (aka true) dependence.
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    ///
124
    bool isFlow() const;
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    /// isAnti - Returns true if this is an anti dependence.
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    ///
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    bool isAnti() const;
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    /// isOrdered - Returns true if dependence is Output, Flow, or Anti
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    ///
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0
    bool isOrdered() const { return isOutput() || isFlow() || isAnti(); }
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    /// isUnordered - Returns true if dependence is Input
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    ///
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0
    bool isUnordered() const { return isInput(); }
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    /// isLoopIndependent - Returns true if this is a loop-independent
139
    /// dependence.
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0
    virtual bool isLoopIndependent() const { return true; }
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    /// isConfused - Returns true if this dependence is confused
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    /// (the compiler understands nothing and makes worst-case
144
    /// assumptions).
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847
    virtual bool isConfused() const { return true; }
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    /// isConsistent - Returns true if this dependence is consistent
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    /// (occurs every time the source and destination are executed).
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0
    virtual bool isConsistent() const { return false; }
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    /// getLevels - Returns the number of common loops surrounding the
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    /// source and destination of the dependence.
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849
    virtual unsigned getLevels() const { return 0; }
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    /// getDirection - Returns the direction associated with a particular
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    /// level.
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    virtual unsigned getDirection(unsigned Level) const { return DVEntry::ALL; }
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    /// getDistance - Returns the distance (or NULL) associated with a
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    /// particular level.
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    virtual const SCEV *getDistance(unsigned Level) const { return nullptr; }
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    /// isPeelFirst - Returns true if peeling the first iteration from
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    /// this loop will break this dependence.
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0
    virtual bool isPeelFirst(unsigned Level) const { return false; }
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    /// isPeelLast - Returns true if peeling the last iteration from
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    /// this loop will break this dependence.
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0
    virtual bool isPeelLast(unsigned Level) const { return false; }
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    /// isSplitable - Returns true if splitting this loop will break
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    /// the dependence.
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0
    virtual bool isSplitable(unsigned Level) const { return false; }
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    /// isScalar - Returns true if a particular level is scalar; that is,
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    /// if no subscript in the source or destination mention the induction
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    /// variable associated with the loop at this level.
178
    virtual bool isScalar(unsigned Level) const;
179
180
    /// getNextPredecessor - Returns the value of the NextPredecessor
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    /// field.
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0
    const Dependence *getNextPredecessor() const { return NextPredecessor; }
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    /// getNextSuccessor - Returns the value of the NextSuccessor
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    /// field.
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0
    const Dependence *getNextSuccessor() const { return NextSuccessor; }
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    /// setNextPredecessor - Sets the value of the NextPredecessor
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    /// field.
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0
    void setNextPredecessor(const Dependence *pred) { NextPredecessor = pred; }
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    /// setNextSuccessor - Sets the value of the NextSuccessor
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    /// field.
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0
    void setNextSuccessor(const Dependence *succ) { NextSuccessor = succ; }
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    /// dump - For debugging purposes, dumps a dependence to OS.
197
    ///
198
    void dump(raw_ostream &OS) const;
199
200
  private:
201
    Instruction *Src, *Dst;
202
    const Dependence *NextPredecessor, *NextSuccessor;
203
    friend class DependenceInfo;
204
  };
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206
  /// FullDependence - This class represents a dependence between two memory
207
  /// references in a function. It contains detailed information about the
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  /// dependence (direction vectors, etc.) and is used when the compiler is
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  /// able to accurately analyze the interaction of the references; that is,
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  /// it is not a confused dependence (see Dependence). In most cases
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  /// (for output, flow, and anti dependences), the dependence implies an
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  /// ordering, where the source must precede the destination; in contrast,
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  /// input dependences are unordered.
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  class FullDependence final : public Dependence {
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  public:
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    FullDependence(Instruction *Src, Instruction *Dst, bool LoopIndependent,
217
                   unsigned Levels);
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219
    /// isLoopIndependent - Returns true if this is a loop-independent
220
    /// dependence.
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622
    bool isLoopIndependent() const override { return LoopIndependent; }
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    /// isConfused - Returns true if this dependence is confused
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    /// (the compiler understands nothing and makes worst-case
225
    /// assumptions).
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    bool isConfused() const override { return false; }
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    /// isConsistent - Returns true if this dependence is consistent
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    /// (occurs every time the source and destination are executed).
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    bool isConsistent() const override { return Consistent; }
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    /// getLevels - Returns the number of common loops surrounding the
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    /// source and destination of the dependence.
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2.40k
    unsigned getLevels() const override { return Levels; }
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    /// getDirection - Returns the direction associated with a particular
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    /// level.
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    unsigned getDirection(unsigned Level) const override;
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    /// getDistance - Returns the distance (or NULL) associated with a
241
    /// particular level.
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    const SCEV *getDistance(unsigned Level) const override;
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    /// isPeelFirst - Returns true if peeling the first iteration from
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    /// this loop will break this dependence.
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    bool isPeelFirst(unsigned Level) const override;
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    /// isPeelLast - Returns true if peeling the last iteration from
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    /// this loop will break this dependence.
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    bool isPeelLast(unsigned Level) const override;
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    /// isSplitable - Returns true if splitting the loop will break
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    /// the dependence.
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    bool isSplitable(unsigned Level) const override;
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    /// isScalar - Returns true if a particular level is scalar; that is,
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    /// if no subscript in the source or destination mention the induction
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    /// variable associated with the loop at this level.
259
    bool isScalar(unsigned Level) const override;
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261
  private:
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    unsigned short Levels;
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    bool LoopIndependent;
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    bool Consistent; // Init to true, then refine.
265
    std::unique_ptr<DVEntry[]> DV;
266
    friend class DependenceInfo;
267
  };
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269
  /// DependenceInfo - This class is the main dependence-analysis driver.
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  ///
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  class DependenceInfo {
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  public:
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    DependenceInfo(Function *F, AliasAnalysis *AA, ScalarEvolution *SE,
274
                   LoopInfo *LI)
275
475
        : AA(AA), SE(SE), LI(LI), F(F) {}
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    /// Handle transitive invalidation when the cached analysis results go away.
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    bool invalidate(Function &F, const PreservedAnalyses &PA,
279
                    FunctionAnalysisManager::Invalidator &Inv);
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281
    /// depends - Tests for a dependence between the Src and Dst instructions.
282
    /// Returns NULL if no dependence; otherwise, returns a Dependence (or a
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    /// FullDependence) with as much information as can be gleaned.
284
    /// The flag PossiblyLoopIndependent should be set by the caller
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    /// if it appears that control flow can reach from Src to Dst
286
    /// without traversing a loop back edge.
287
    std::unique_ptr<Dependence> depends(Instruction *Src,
288
                                        Instruction *Dst,
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                                        bool PossiblyLoopIndependent);
290
291
    /// getSplitIteration - Give a dependence that's splittable at some
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    /// particular level, return the iteration that should be used to split
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    /// the loop.
294
    ///
295
    /// Generally, the dependence analyzer will be used to build
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    /// a dependence graph for a function (basically a map from instructions
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    /// to dependences). Looking for cycles in the graph shows us loops
298
    /// that cannot be trivially vectorized/parallelized.
299
    ///
300
    /// We can try to improve the situation by examining all the dependences
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    /// that make up the cycle, looking for ones we can break.
302
    /// Sometimes, peeling the first or last iteration of a loop will break
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    /// dependences, and there are flags for those possibilities.
304
    /// Sometimes, splitting a loop at some other iteration will do the trick,
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    /// and we've got a flag for that case. Rather than waste the space to
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    /// record the exact iteration (since we rarely know), we provide
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    /// a method that calculates the iteration. It's a drag that it must work
308
    /// from scratch, but wonderful in that it's possible.
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    ///
310
    /// Here's an example:
311
    ///
312
    ///    for (i = 0; i < 10; i++)
313
    ///        A[i] = ...
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    ///        ... = A[11 - i]
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    ///
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    /// There's a loop-carried flow dependence from the store to the load,
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    /// found by the weak-crossing SIV test. The dependence will have a flag,
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    /// indicating that the dependence can be broken by splitting the loop.
319
    /// Calling getSplitIteration will return 5.
320
    /// Splitting the loop breaks the dependence, like so:
321
    ///
322
    ///    for (i = 0; i <= 5; i++)
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    ///        A[i] = ...
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    ///        ... = A[11 - i]
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    ///    for (i = 6; i < 10; i++)
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    ///        A[i] = ...
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    ///        ... = A[11 - i]
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    ///
329
    /// breaks the dependence and allows us to vectorize/parallelize
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    /// both loops.
331
    const SCEV *getSplitIteration(const Dependence &Dep, unsigned Level);
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333
383
    Function *getFunction() const { return F; }
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  private:
336
    AliasAnalysis *AA;
337
    ScalarEvolution *SE;
338
    LoopInfo *LI;
339
    Function *F;
340
341
    /// Subscript - This private struct represents a pair of subscripts from
342
    /// a pair of potentially multi-dimensional array references. We use a
343
    /// vector of them to guide subscript partitioning.
344
    struct Subscript {
345
      const SCEV *Src;
346
      const SCEV *Dst;
347
      enum ClassificationKind { ZIV, SIV, RDIV, MIV, NonLinear } Classification;
348
      SmallBitVector Loops;
349
      SmallBitVector GroupLoops;
350
      SmallBitVector Group;
351
    };
352
353
    struct CoefficientInfo {
354
      const SCEV *Coeff;
355
      const SCEV *PosPart;
356
      const SCEV *NegPart;
357
      const SCEV *Iterations;
358
    };
359
360
    struct BoundInfo {
361
      const SCEV *Iterations;
362
      const SCEV *Upper[8];
363
      const SCEV *Lower[8];
364
      unsigned char Direction;
365
      unsigned char DirSet;
366
    };
367
368
    /// Constraint - This private class represents a constraint, as defined
369
    /// in the paper
370
    ///
371
    ///           Practical Dependence Testing
372
    ///           Goff, Kennedy, Tseng
373
    ///           PLDI 1991
374
    ///
375
    /// There are 5 kinds of constraint, in a hierarchy.
376
    ///   1) Any - indicates no constraint, any dependence is possible.
377
    ///   2) Line - A line ax + by = c, where a, b, and c are parameters,
378
    ///             representing the dependence equation.
379
    ///   3) Distance - The value d of the dependence distance;
380
    ///   4) Point - A point <x, y> representing the dependence from
381
    ///              iteration x to iteration y.
382
    ///   5) Empty - No dependence is possible.
383
    class Constraint {
384
    private:
385
      enum ConstraintKind { Empty, Point, Distance, Line, Any } Kind;
386
      ScalarEvolution *SE;
387
      const SCEV *A;
388
      const SCEV *B;
389
      const SCEV *C;
390
      const Loop *AssociatedLoop;
391
392
    public:
393
      /// isEmpty - Return true if the constraint is of kind Empty.
394
8
      bool isEmpty() const { return Kind == Empty; }
395
396
      /// isPoint - Return true if the constraint is of kind Point.
397
2
      bool isPoint() const { return Kind == Point; }
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399
      /// isDistance - Return true if the constraint is of kind Distance.
400
4
      bool isDistance() const { return Kind == Distance; }
401
402
      /// isLine - Return true if the constraint is of kind Line.
403
      /// Since Distance's can also be represented as Lines, we also return
404
      /// true if the constraint is of kind Distance.
405
6
      bool isLine() const { return Kind == Line || 
Kind == Distance2
; }
406
407
      /// isAny - Return true if the constraint is of kind Any;
408
8
      bool isAny() const { return Kind == Any; }
409
410
      /// getX - If constraint is a point <X, Y>, returns X.
411
      /// Otherwise assert.
412
      const SCEV *getX() const;
413
414
      /// getY - If constraint is a point <X, Y>, returns Y.
415
      /// Otherwise assert.
416
      const SCEV *getY() const;
417
418
      /// getA - If constraint is a line AX + BY = C, returns A.
419
      /// Otherwise assert.
420
      const SCEV *getA() const;
421
422
      /// getB - If constraint is a line AX + BY = C, returns B.
423
      /// Otherwise assert.
424
      const SCEV *getB() const;
425
426
      /// getC - If constraint is a line AX + BY = C, returns C.
427
      /// Otherwise assert.
428
      const SCEV *getC() const;
429
430
      /// getD - If constraint is a distance, returns D.
431
      /// Otherwise assert.
432
      const SCEV *getD() const;
433
434
      /// getAssociatedLoop - Returns the loop associated with this constraint.
435
      const Loop *getAssociatedLoop() const;
436
437
      /// setPoint - Change a constraint to Point.
438
      void setPoint(const SCEV *X, const SCEV *Y, const Loop *CurrentLoop);
439
440
      /// setLine - Change a constraint to Line.
441
      void setLine(const SCEV *A, const SCEV *B,
442
                   const SCEV *C, const Loop *CurrentLoop);
443
444
      /// setDistance - Change a constraint to Distance.
445
      void setDistance(const SCEV *D, const Loop *CurrentLoop);
446
447
      /// setEmpty - Change a constraint to Empty.
448
      void setEmpty();
449
450
      /// setAny - Change a constraint to Any.
451
      void setAny(ScalarEvolution *SE);
452
453
      /// dump - For debugging purposes. Dumps the constraint
454
      /// out to OS.
455
      void dump(raw_ostream &OS) const;
456
    };
457
458
    /// establishNestingLevels - Examines the loop nesting of the Src and Dst
459
    /// instructions and establishes their shared loops. Sets the variables
460
    /// CommonLevels, SrcLevels, and MaxLevels.
461
    /// The source and destination instructions needn't be contained in the same
462
    /// loop. The routine establishNestingLevels finds the level of most deeply
463
    /// nested loop that contains them both, CommonLevels. An instruction that's
464
    /// not contained in a loop is at level = 0. MaxLevels is equal to the level
465
    /// of the source plus the level of the destination, minus CommonLevels.
466
    /// This lets us allocate vectors MaxLevels in length, with room for every
467
    /// distinct loop referenced in both the source and destination subscripts.
468
    /// The variable SrcLevels is the nesting depth of the source instruction.
469
    /// It's used to help calculate distinct loops referenced by the destination.
470
    /// Here's the map from loops to levels:
471
    ///            0 - unused
472
    ///            1 - outermost common loop
473
    ///          ... - other common loops
474
    /// CommonLevels - innermost common loop
475
    ///          ... - loops containing Src but not Dst
476
    ///    SrcLevels - innermost loop containing Src but not Dst
477
    ///          ... - loops containing Dst but not Src
478
    ///    MaxLevels - innermost loop containing Dst but not Src
479
    /// Consider the follow code fragment:
480
    ///    for (a = ...) {
481
    ///      for (b = ...) {
482
    ///        for (c = ...) {
483
    ///          for (d = ...) {
484
    ///            A[] = ...;
485
    ///          }
486
    ///        }
487
    ///        for (e = ...) {
488
    ///          for (f = ...) {
489
    ///            for (g = ...) {
490
    ///              ... = A[];
491
    ///            }
492
    ///          }
493
    ///        }
494
    ///      }
495
    ///    }
496
    /// If we're looking at the possibility of a dependence between the store
497
    /// to A (the Src) and the load from A (the Dst), we'll note that they
498
    /// have 2 loops in common, so CommonLevels will equal 2 and the direction
499
    /// vector for Result will have 2 entries. SrcLevels = 4 and MaxLevels = 7.
500
    /// A map from loop names to level indices would look like
501
    ///     a - 1
502
    ///     b - 2 = CommonLevels
503
    ///     c - 3
504
    ///     d - 4 = SrcLevels
505
    ///     e - 5
506
    ///     f - 6
507
    ///     g - 7 = MaxLevels
508
    void establishNestingLevels(const Instruction *Src,
509
                                const Instruction *Dst);
510
511
    unsigned CommonLevels, SrcLevels, MaxLevels;
512
513
    /// mapSrcLoop - Given one of the loops containing the source, return
514
    /// its level index in our numbering scheme.
515
    unsigned mapSrcLoop(const Loop *SrcLoop) const;
516
517
    /// mapDstLoop - Given one of the loops containing the destination,
518
    /// return its level index in our numbering scheme.
519
    unsigned mapDstLoop(const Loop *DstLoop) const;
520
521
    /// isLoopInvariant - Returns true if Expression is loop invariant
522
    /// in LoopNest.
523
    bool isLoopInvariant(const SCEV *Expression, const Loop *LoopNest) const;
524
525
    /// Makes sure all subscript pairs share the same integer type by
526
    /// sign-extending as necessary.
527
    /// Sign-extending a subscript is safe because getelementptr assumes the
528
    /// array subscripts are signed.
529
    void unifySubscriptType(ArrayRef<Subscript *> Pairs);
530
531
    /// removeMatchingExtensions - Examines a subscript pair.
532
    /// If the source and destination are identically sign (or zero)
533
    /// extended, it strips off the extension in an effort to
534
    /// simplify the actual analysis.
535
    void removeMatchingExtensions(Subscript *Pair);
536
537
    /// collectCommonLoops - Finds the set of loops from the LoopNest that
538
    /// have a level <= CommonLevels and are referred to by the SCEV Expression.
539
    void collectCommonLoops(const SCEV *Expression,
540
                            const Loop *LoopNest,
541
                            SmallBitVector &Loops) const;
542
543
    /// checkSrcSubscript - Examines the SCEV Src, returning true iff it's
544
    /// linear. Collect the set of loops mentioned by Src.
545
    bool checkSrcSubscript(const SCEV *Src,
546
                           const Loop *LoopNest,
547
                           SmallBitVector &Loops);
548
549
    /// checkDstSubscript - Examines the SCEV Dst, returning true iff it's
550
    /// linear. Collect the set of loops mentioned by Dst.
551
    bool checkDstSubscript(const SCEV *Dst,
552
                           const Loop *LoopNest,
553
                           SmallBitVector &Loops);
554
555
    /// isKnownPredicate - Compare X and Y using the predicate Pred.
556
    /// Basically a wrapper for SCEV::isKnownPredicate,
557
    /// but tries harder, especially in the presence of sign and zero
558
    /// extensions and symbolics.
559
    bool isKnownPredicate(ICmpInst::Predicate Pred,
560
                          const SCEV *X,
561
                          const SCEV *Y) const;
562
563
    /// isKnownLessThan - Compare to see if S is less than Size
564
    /// Another wrapper for isKnownNegative(S - max(Size, 1)) with some extra
565
    /// checking if S is an AddRec and we can prove lessthan using the loop
566
    /// bounds.
567
    bool isKnownLessThan(const SCEV *S, const SCEV *Size) const;
568
569
    /// isKnownNonNegative - Compare to see if S is known not to be negative
570
    /// Uses the fact that S comes from Ptr, which may be an inbound GEP,
571
    /// Proving there is no wrapping going on.
572
    bool isKnownNonNegative(const SCEV *S, const Value *Ptr) const;
573
574
    /// collectUpperBound - All subscripts are the same type (on my machine,
575
    /// an i64). The loop bound may be a smaller type. collectUpperBound
576
    /// find the bound, if available, and zero extends it to the Type T.
577
    /// (I zero extend since the bound should always be >= 0.)
578
    /// If no upper bound is available, return NULL.
579
    const SCEV *collectUpperBound(const Loop *l, Type *T) const;
580
581
    /// collectConstantUpperBound - Calls collectUpperBound(), then
582
    /// attempts to cast it to SCEVConstant. If the cast fails,
583
    /// returns NULL.
584
    const SCEVConstant *collectConstantUpperBound(const Loop *l, Type *T) const;
585
586
    /// classifyPair - Examines the subscript pair (the Src and Dst SCEVs)
587
    /// and classifies it as either ZIV, SIV, RDIV, MIV, or Nonlinear.
588
    /// Collects the associated loops in a set.
589
    Subscript::ClassificationKind classifyPair(const SCEV *Src,
590
                                           const Loop *SrcLoopNest,
591
                                           const SCEV *Dst,
592
                                           const Loop *DstLoopNest,
593
                                           SmallBitVector &Loops);
594
595
    /// testZIV - Tests the ZIV subscript pair (Src and Dst) for dependence.
596
    /// Returns true if any possible dependence is disproved.
597
    /// If there might be a dependence, returns false.
598
    /// If the dependence isn't proven to exist,
599
    /// marks the Result as inconsistent.
600
    bool testZIV(const SCEV *Src,
601
                 const SCEV *Dst,
602
                 FullDependence &Result) const;
603
604
    /// testSIV - Tests the SIV subscript pair (Src and Dst) for dependence.
605
    /// Things of the form [c1 + a1*i] and [c2 + a2*j], where
606
    /// i and j are induction variables, c1 and c2 are loop invariant,
607
    /// and a1 and a2 are constant.
608
    /// Returns true if any possible dependence is disproved.
609
    /// If there might be a dependence, returns false.
610
    /// Sets appropriate direction vector entry and, when possible,
611
    /// the distance vector entry.
612
    /// If the dependence isn't proven to exist,
613
    /// marks the Result as inconsistent.
614
    bool testSIV(const SCEV *Src,
615
                 const SCEV *Dst,
616
                 unsigned &Level,
617
                 FullDependence &Result,
618
                 Constraint &NewConstraint,
619
                 const SCEV *&SplitIter) const;
620
621
    /// testRDIV - Tests the RDIV subscript pair (Src and Dst) for dependence.
622
    /// Things of the form [c1 + a1*i] and [c2 + a2*j]
623
    /// where i and j are induction variables, c1 and c2 are loop invariant,
624
    /// and a1 and a2 are constant.
625
    /// With minor algebra, this test can also be used for things like
626
    /// [c1 + a1*i + a2*j][c2].
627
    /// Returns true if any possible dependence is disproved.
628
    /// If there might be a dependence, returns false.
629
    /// Marks the Result as inconsistent.
630
    bool testRDIV(const SCEV *Src,
631
                  const SCEV *Dst,
632
                  FullDependence &Result) const;
633
634
    /// testMIV - Tests the MIV subscript pair (Src and Dst) for dependence.
635
    /// Returns true if dependence disproved.
636
    /// Can sometimes refine direction vectors.
637
    bool testMIV(const SCEV *Src,
638
                 const SCEV *Dst,
639
                 const SmallBitVector &Loops,
640
                 FullDependence &Result) const;
641
642
    /// strongSIVtest - Tests the strong SIV subscript pair (Src and Dst)
643
    /// for dependence.
644
    /// Things of the form [c1 + a*i] and [c2 + a*i],
645
    /// where i is an induction variable, c1 and c2 are loop invariant,
646
    /// and a is a constant
647
    /// Returns true if any possible dependence is disproved.
648
    /// If there might be a dependence, returns false.
649
    /// Sets appropriate direction and distance.
650
    bool strongSIVtest(const SCEV *Coeff,
651
                       const SCEV *SrcConst,
652
                       const SCEV *DstConst,
653
                       const Loop *CurrentLoop,
654
                       unsigned Level,
655
                       FullDependence &Result,
656
                       Constraint &NewConstraint) const;
657
658
    /// weakCrossingSIVtest - Tests the weak-crossing SIV subscript pair
659
    /// (Src and Dst) for dependence.
660
    /// Things of the form [c1 + a*i] and [c2 - a*i],
661
    /// where i is an induction variable, c1 and c2 are loop invariant,
662
    /// and a is a constant.
663
    /// Returns true if any possible dependence is disproved.
664
    /// If there might be a dependence, returns false.
665
    /// Sets appropriate direction entry.
666
    /// Set consistent to false.
667
    /// Marks the dependence as splitable.
668
    bool weakCrossingSIVtest(const SCEV *SrcCoeff,
669
                             const SCEV *SrcConst,
670
                             const SCEV *DstConst,
671
                             const Loop *CurrentLoop,
672
                             unsigned Level,
673
                             FullDependence &Result,
674
                             Constraint &NewConstraint,
675
                             const SCEV *&SplitIter) const;
676
677
    /// ExactSIVtest - Tests the SIV subscript pair
678
    /// (Src and Dst) for dependence.
679
    /// Things of the form [c1 + a1*i] and [c2 + a2*i],
680
    /// where i is an induction variable, c1 and c2 are loop invariant,
681
    /// and a1 and a2 are constant.
682
    /// Returns true if any possible dependence is disproved.
683
    /// If there might be a dependence, returns false.
684
    /// Sets appropriate direction entry.
685
    /// Set consistent to false.
686
    bool exactSIVtest(const SCEV *SrcCoeff,
687
                      const SCEV *DstCoeff,
688
                      const SCEV *SrcConst,
689
                      const SCEV *DstConst,
690
                      const Loop *CurrentLoop,
691
                      unsigned Level,
692
                      FullDependence &Result,
693
                      Constraint &NewConstraint) const;
694
695
    /// weakZeroSrcSIVtest - Tests the weak-zero SIV subscript pair
696
    /// (Src and Dst) for dependence.
697
    /// Things of the form [c1] and [c2 + a*i],
698
    /// where i is an induction variable, c1 and c2 are loop invariant,
699
    /// and a is a constant. See also weakZeroDstSIVtest.
700
    /// Returns true if any possible dependence is disproved.
701
    /// If there might be a dependence, returns false.
702
    /// Sets appropriate direction entry.
703
    /// Set consistent to false.
704
    /// If loop peeling will break the dependence, mark appropriately.
705
    bool weakZeroSrcSIVtest(const SCEV *DstCoeff,
706
                            const SCEV *SrcConst,
707
                            const SCEV *DstConst,
708
                            const Loop *CurrentLoop,
709
                            unsigned Level,
710
                            FullDependence &Result,
711
                            Constraint &NewConstraint) const;
712
713
    /// weakZeroDstSIVtest - Tests the weak-zero SIV subscript pair
714
    /// (Src and Dst) for dependence.
715
    /// Things of the form [c1 + a*i] and [c2],
716
    /// where i is an induction variable, c1 and c2 are loop invariant,
717
    /// and a is a constant. See also weakZeroSrcSIVtest.
718
    /// Returns true if any possible dependence is disproved.
719
    /// If there might be a dependence, returns false.
720
    /// Sets appropriate direction entry.
721
    /// Set consistent to false.
722
    /// If loop peeling will break the dependence, mark appropriately.
723
    bool weakZeroDstSIVtest(const SCEV *SrcCoeff,
724
                            const SCEV *SrcConst,
725
                            const SCEV *DstConst,
726
                            const Loop *CurrentLoop,
727
                            unsigned Level,
728
                            FullDependence &Result,
729
                            Constraint &NewConstraint) const;
730
731
    /// exactRDIVtest - Tests the RDIV subscript pair for dependence.
732
    /// Things of the form [c1 + a*i] and [c2 + b*j],
733
    /// where i and j are induction variable, c1 and c2 are loop invariant,
734
    /// and a and b are constants.
735
    /// Returns true if any possible dependence is disproved.
736
    /// Marks the result as inconsistent.
737
    /// Works in some cases that symbolicRDIVtest doesn't,
738
    /// and vice versa.
739
    bool exactRDIVtest(const SCEV *SrcCoeff,
740
                       const SCEV *DstCoeff,
741
                       const SCEV *SrcConst,
742
                       const SCEV *DstConst,
743
                       const Loop *SrcLoop,
744
                       const Loop *DstLoop,
745
                       FullDependence &Result) const;
746
747
    /// symbolicRDIVtest - Tests the RDIV subscript pair for dependence.
748
    /// Things of the form [c1 + a*i] and [c2 + b*j],
749
    /// where i and j are induction variable, c1 and c2 are loop invariant,
750
    /// and a and b are constants.
751
    /// Returns true if any possible dependence is disproved.
752
    /// Marks the result as inconsistent.
753
    /// Works in some cases that exactRDIVtest doesn't,
754
    /// and vice versa. Can also be used as a backup for
755
    /// ordinary SIV tests.
756
    bool symbolicRDIVtest(const SCEV *SrcCoeff,
757
                          const SCEV *DstCoeff,
758
                          const SCEV *SrcConst,
759
                          const SCEV *DstConst,
760
                          const Loop *SrcLoop,
761
                          const Loop *DstLoop) const;
762
763
    /// gcdMIVtest - Tests an MIV subscript pair for dependence.
764
    /// Returns true if any possible dependence is disproved.
765
    /// Marks the result as inconsistent.
766
    /// Can sometimes disprove the equal direction for 1 or more loops.
767
    //  Can handle some symbolics that even the SIV tests don't get,
768
    /// so we use it as a backup for everything.
769
    bool gcdMIVtest(const SCEV *Src,
770
                    const SCEV *Dst,
771
                    FullDependence &Result) const;
772
773
    /// banerjeeMIVtest - Tests an MIV subscript pair for dependence.
774
    /// Returns true if any possible dependence is disproved.
775
    /// Marks the result as inconsistent.
776
    /// Computes directions.
777
    bool banerjeeMIVtest(const SCEV *Src,
778
                         const SCEV *Dst,
779
                         const SmallBitVector &Loops,
780
                         FullDependence &Result) const;
781
782
    /// collectCoefficientInfo - Walks through the subscript,
783
    /// collecting each coefficient, the associated loop bounds,
784
    /// and recording its positive and negative parts for later use.
785
    CoefficientInfo *collectCoeffInfo(const SCEV *Subscript,
786
                                      bool SrcFlag,
787
                                      const SCEV *&Constant) const;
788
789
    /// getPositivePart - X^+ = max(X, 0).
790
    ///
791
    const SCEV *getPositivePart(const SCEV *X) const;
792
793
    /// getNegativePart - X^- = min(X, 0).
794
    ///
795
    const SCEV *getNegativePart(const SCEV *X) const;
796
797
    /// getLowerBound - Looks through all the bounds info and
798
    /// computes the lower bound given the current direction settings
799
    /// at each level.
800
    const SCEV *getLowerBound(BoundInfo *Bound) const;
801
802
    /// getUpperBound - Looks through all the bounds info and
803
    /// computes the upper bound given the current direction settings
804
    /// at each level.
805
    const SCEV *getUpperBound(BoundInfo *Bound) const;
806
807
    /// exploreDirections - Hierarchically expands the direction vector
808
    /// search space, combining the directions of discovered dependences
809
    /// in the DirSet field of Bound. Returns the number of distinct
810
    /// dependences discovered. If the dependence is disproved,
811
    /// it will return 0.
812
    unsigned exploreDirections(unsigned Level,
813
                               CoefficientInfo *A,
814
                               CoefficientInfo *B,
815
                               BoundInfo *Bound,
816
                               const SmallBitVector &Loops,
817
                               unsigned &DepthExpanded,
818
                               const SCEV *Delta) const;
819
820
    /// testBounds - Returns true iff the current bounds are plausible.
821
    bool testBounds(unsigned char DirKind,
822
                    unsigned Level,
823
                    BoundInfo *Bound,
824
                    const SCEV *Delta) const;
825
826
    /// findBoundsALL - Computes the upper and lower bounds for level K
827
    /// using the * direction. Records them in Bound.
828
    void findBoundsALL(CoefficientInfo *A,
829
                       CoefficientInfo *B,
830
                       BoundInfo *Bound,
831
                       unsigned K) const;
832
833
    /// findBoundsLT - Computes the upper and lower bounds for level K
834
    /// using the < direction. Records them in Bound.
835
    void findBoundsLT(CoefficientInfo *A,
836
                      CoefficientInfo *B,
837
                      BoundInfo *Bound,
838
                      unsigned K) const;
839
840
    /// findBoundsGT - Computes the upper and lower bounds for level K
841
    /// using the > direction. Records them in Bound.
842
    void findBoundsGT(CoefficientInfo *A,
843
                      CoefficientInfo *B,
844
                      BoundInfo *Bound,
845
                      unsigned K) const;
846
847
    /// findBoundsEQ - Computes the upper and lower bounds for level K
848
    /// using the = direction. Records them in Bound.
849
    void findBoundsEQ(CoefficientInfo *A,
850
                      CoefficientInfo *B,
851
                      BoundInfo *Bound,
852
                      unsigned K) const;
853
854
    /// intersectConstraints - Updates X with the intersection
855
    /// of the Constraints X and Y. Returns true if X has changed.
856
    bool intersectConstraints(Constraint *X,
857
                              const Constraint *Y);
858
859
    /// propagate - Review the constraints, looking for opportunities
860
    /// to simplify a subscript pair (Src and Dst).
861
    /// Return true if some simplification occurs.
862
    /// If the simplification isn't exact (that is, if it is conservative
863
    /// in terms of dependence), set consistent to false.
864
    bool propagate(const SCEV *&Src,
865
                   const SCEV *&Dst,
866
                   SmallBitVector &Loops,
867
                   SmallVectorImpl<Constraint> &Constraints,
868
                   bool &Consistent);
869
870
    /// propagateDistance - Attempt to propagate a distance
871
    /// constraint into a subscript pair (Src and Dst).
872
    /// Return true if some simplification occurs.
873
    /// If the simplification isn't exact (that is, if it is conservative
874
    /// in terms of dependence), set consistent to false.
875
    bool propagateDistance(const SCEV *&Src,
876
                           const SCEV *&Dst,
877
                           Constraint &CurConstraint,
878
                           bool &Consistent);
879
880
    /// propagatePoint - Attempt to propagate a point
881
    /// constraint into a subscript pair (Src and Dst).
882
    /// Return true if some simplification occurs.
883
    bool propagatePoint(const SCEV *&Src,
884
                        const SCEV *&Dst,
885
                        Constraint &CurConstraint);
886
887
    /// propagateLine - Attempt to propagate a line
888
    /// constraint into a subscript pair (Src and Dst).
889
    /// Return true if some simplification occurs.
890
    /// If the simplification isn't exact (that is, if it is conservative
891
    /// in terms of dependence), set consistent to false.
892
    bool propagateLine(const SCEV *&Src,
893
                       const SCEV *&Dst,
894
                       Constraint &CurConstraint,
895
                       bool &Consistent);
896
897
    /// findCoefficient - Given a linear SCEV,
898
    /// return the coefficient corresponding to specified loop.
899
    /// If there isn't one, return the SCEV constant 0.
900
    /// For example, given a*i + b*j + c*k, returning the coefficient
901
    /// corresponding to the j loop would yield b.
902
    const SCEV *findCoefficient(const SCEV *Expr,
903
                                const Loop *TargetLoop) const;
904
905
    /// zeroCoefficient - Given a linear SCEV,
906
    /// return the SCEV given by zeroing out the coefficient
907
    /// corresponding to the specified loop.
908
    /// For example, given a*i + b*j + c*k, zeroing the coefficient
909
    /// corresponding to the j loop would yield a*i + c*k.
910
    const SCEV *zeroCoefficient(const SCEV *Expr,
911
                                const Loop *TargetLoop) const;
912
913
    /// addToCoefficient - Given a linear SCEV Expr,
914
    /// return the SCEV given by adding some Value to the
915
    /// coefficient corresponding to the specified TargetLoop.
916
    /// For example, given a*i + b*j + c*k, adding 1 to the coefficient
917
    /// corresponding to the j loop would yield a*i + (b+1)*j + c*k.
918
    const SCEV *addToCoefficient(const SCEV *Expr,
919
                                 const Loop *TargetLoop,
920
                                 const SCEV *Value)  const;
921
922
    /// updateDirection - Update direction vector entry
923
    /// based on the current constraint.
924
    void updateDirection(Dependence::DVEntry &Level,
925
                         const Constraint &CurConstraint) const;
926
927
    bool tryDelinearize(Instruction *Src, Instruction *Dst,
928
                        SmallVectorImpl<Subscript> &Pair);
929
  }; // class DependenceInfo
930
931
  /// AnalysisPass to compute dependence information in a function
932
  class DependenceAnalysis : public AnalysisInfoMixin<DependenceAnalysis> {
933
  public:
934
    typedef DependenceInfo Result;
935
    Result run(Function &F, FunctionAnalysisManager &FAM);
936
937
  private:
938
    static AnalysisKey Key;
939
    friend struct AnalysisInfoMixin<DependenceAnalysis>;
940
  }; // class DependenceAnalysis
941
942
  /// Printer pass to dump DA results.
943
  struct DependenceAnalysisPrinterPass
944
      : public PassInfoMixin<DependenceAnalysisPrinterPass> {
945
27
    DependenceAnalysisPrinterPass(raw_ostream &OS) : OS(OS) {}
946
947
    PreservedAnalyses run(Function &F, FunctionAnalysisManager &FAM);
948
949
  private:
950
    raw_ostream &OS;
951
  }; // class DependenceAnalysisPrinterPass
952
953
  /// Legacy pass manager pass to access dependence information
954
  class DependenceAnalysisWrapperPass : public FunctionPass {
955
  public:
956
    static char ID; // Class identification, replacement for typeinfo
957
50
    DependenceAnalysisWrapperPass() : FunctionPass(ID) {
958
50
      initializeDependenceAnalysisWrapperPassPass(
959
50
          *PassRegistry::getPassRegistry());
960
50
    }
961
962
    bool runOnFunction(Function &F) override;
963
    void releaseMemory() override;
964
    void getAnalysisUsage(AnalysisUsage &) const override;
965
    void print(raw_ostream &, const Module * = nullptr) const override;
966
    DependenceInfo &getDI() const;
967
968
  private:
969
    std::unique_ptr<DependenceInfo> info;
970
  }; // class DependenceAnalysisWrapperPass
971
972
  /// createDependenceAnalysisPass - This creates an instance of the
973
  /// DependenceAnalysis wrapper pass.
974
  FunctionPass *createDependenceAnalysisWrapperPass();
975
976
} // namespace llvm
977
978
#endif