dependence analysis

Patch from Preston Briggs <preston.briggs@gmail.com>.

This is an updated version of the dependence-analysis patch, including an MIV
test based on Banerjee's inequalities.

It's a fairly complete implementation of the paper

    Practical Dependence Testing
    Gina Goff, Ken Kennedy, and Chau-Wen Tseng
    PLDI 1991

It cannot yet propagate constraints between coupled RDIV subscripts (discussed
in Section 5.3.2 of the paper).

It's organized as a FunctionPass with a single entry point that supports testing
for dependence between two instructions in a function. If there's no dependence,
it returns null. If there's a dependence, it returns a pointer to a Dependence
which can be queried about details (what kind of dependence, is it loop
independent, direction and distance vector entries, etc). I haven't included
every imaginable feature, but there's a good selection that should be adequate
for supporting many loop transformations. Of course, it can be extended as
necessary.

Included in the patch file are many test cases, commented with C code showing
the loops and array references.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165708 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 902 insertions, 0 deletions

diff --git a/include/llvm/Analysis/DependenceAnalysis.h b/include/llvm/Analysis/DependenceAnalysis.h
new file mode 100644
index 0000000..0abf6d8
--- /dev/null
+++ b/include/llvm/Analysis/DependenceAnalysis.h
@@ -0,0 +1,891 @@
+//===-- llvm/Analysis/DependenceAnalysis.h -------------------- -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// DependenceAnalysis is an LLVM pass that analyses dependences between memory
+// accesses. Currently, it is an implementation of the approach described in
+//
+//            Practical Dependence Testing
+//            Goff, Kennedy, Tseng
+//            PLDI 1991
+//
+// There's a single entry point that analyzes the dependence between a pair
+// of memory references in a function, returning either NULL, for no dependence,
+// or a more-or-less detailed description of the dependence between them.
+//
+// Please note that this is work in progress and the interface is subject to
+// change.
+//
+// Plausible changes:
+//    Return a set of more precise dependences instead of just one dependence
+//    summarizing all.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_DEPENDENCEANALYSIS_H
+#define LLVM_ANALYSIS_DEPENDENCEANALYSIS_H
+
+#include "llvm/BasicBlock.h"
+#include "llvm/Function.h"
+#include "llvm/Instruction.h"
+#include "llvm/Pass.h"
+#include "llvm/ADT/SmallBitVector.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Support/raw_ostream.h"
+
+
+namespace llvm {
+  class AliasAnalysis;
+  class ScalarEvolution;
+  class SCEV;
+  class Value;
+  class raw_ostream;
+
+  /// Dependence - This class represents a dependence between two memory
+  /// memory references in a function. It contains minimal information and
+  /// is used in the very common situation where the compiler is unable to
+  /// determine anything beyond the existence of a dependence; that is, it
+  /// represents a confused dependence (see also FullDependence). In most
+  /// cases (for output, flow, and anti dependences), the dependence implies
+  /// an ordering, where the source must preceed the destination; in contrast,
+  /// input dependences are unordered.
+  class Dependence {
+  public:
+    Dependence(const Instruction *Source,
+               const Instruction *Destination) :
+      Src(Source), Dst(Destination) {}
+    virtual ~Dependence() {}
+
+    /// Dependence::DVEntry - Each level in the distance/direction vector
+    /// has a direction (or perhaps a union of several directions), and
+    /// perhaps a distance.
+    struct DVEntry {
+      enum { NONE = 0,
+             LT = 1,
+             EQ = 2,
+             LE = 3,
+             GT = 4,
+             NE = 5,
+             GE = 6,
+             ALL = 7 };
+      unsigned char Direction : 3; // Init to ALL, then refine.
+      bool Scalar    : 1; // Init to true.
+      bool PeelFirst : 1; // Peeling the first iteration will break dependence.
+      bool PeelLast  : 1; // Peeling the last iteration will break the dependence.
+      bool Splitable : 1; // Splitting the loop will break dependence.
+      const SCEV *Distance; // NULL implies no distance available.
+      DVEntry() : Direction(ALL), Scalar(true), PeelFirst(false),
+                  PeelLast(false), Splitable(false), Distance(NULL) { }
+    };
+
+    /// getSrc - Returns the source instruction for this dependence.
+    ///
+    const Instruction *getSrc() const { return Src; }
+
+    /// getDst - Returns the destination instruction for this dependence.
+    ///
+    const Instruction *getDst() const { return Dst; }
+
+    /// isInput - Returns true if this is an input dependence.
+    ///
+    bool isInput() const;
+
+    /// isOutput - Returns true if this is an output dependence.
+    ///
+    bool isOutput() const;
+
+    /// isFlow - Returns true if this is a flow (aka true) dependence.
+    ///
+    bool isFlow() const;
+
+    /// isAnti - Returns true if this is an anti dependence.
+    ///
+    bool isAnti() const;
+
+    /// isOrdered - Returns true if dependence is Output, Flow, or Anti
+    ///
+    bool isOrdered() const { return isOutput() || isFlow() || isAnti(); }
+
+    /// isUnordered - Returns true if dependence is Input
+    ///
+    bool isUnordered() const { return isInput(); }
+
+    /// isLoopIndependent - Returns true if this is a loop-independent
+    /// dependence.
+    virtual bool isLoopIndependent() const { return true; }
+
+    /// isConfused - Returns true if this dependence is confused
+    /// (the compiler understands nothing and makes worst-case
+    /// assumptions).
+    virtual bool isConfused() const { return true; }
+
+    /// isConsistent - Returns true if this dependence is consistent
+    /// (occurs every time the source and destination are executed).
+    virtual bool isConsistent() const { return false; }
+
+    /// getLevels - Returns the number of common loops surrounding the
+    /// souce and destination of the dependence.
+    virtual unsigned getLevels() const { return 0; }
+
+    /// getDirection - Returns the direction associated with a particular
+    /// level.
+    virtual unsigned getDirection(unsigned Level) const { return DVEntry::ALL; }
+
+    /// getDistance - Returns the distance (or NULL) associated with a
+    /// particular level.
+    virtual const SCEV *getDistance(unsigned Level) const { return NULL; }
+
+    /// isPeelFirst - Returns true if peeling the first iteration from
+    /// this loop will break this dependence.
+    virtual bool isPeelFirst(unsigned Level) const { return false; }
+
+    /// isPeelLast - Returns true if peeling the last iteration from
+    /// this loop will break this dependence.
+    virtual bool isPeelLast(unsigned Level) const { return false; }
+
+    /// isSplitable - Returns true if splitting this loop will break
+    /// the dependence.
+    virtual bool isSplitable(unsigned Level) const { return false; }
+
+    /// isScalar - Returns true if a particular level is scalar; that is,
+    /// if no subscript in the source or destination mention the induction
+    /// variable associated with the loop at this level.
+    virtual bool isScalar(unsigned Level) const;
+
+    /// dump - For debugging purposes, dumps a dependence to OS.
+    ///
+    void dump(raw_ostream &OS) const;
+  private:
+    const Instruction *Src, *Dst;
+    friend class DependenceAnalysis;
+  };
+
+
+  /// FullDependence - This class represents a dependence between two memory
+  /// references in a function. It contains detailed information about the
+  /// dependence (direction vectors, etc) and is used when the compiler is
+  /// able to accurately analyze the interaction of the references; that is,
+  /// it is not a confused dependence (see Dependence). In most cases
+  /// (for output, flow, and anti dependences), the dependence implies an
+  /// ordering, where the source must preceed the destination; in contrast,
+  /// input dependences are unordered.
+  class FullDependence : public Dependence {
+  public:
+    FullDependence(const Instruction *Src,
+                   const Instruction *Dst,
+                   bool LoopIndependent,
+                   unsigned Levels);
+    ~FullDependence() {
+      delete DV;
+    }
+
+    /// isLoopIndependent - Returns true if this is a loop-independent
+    /// dependence.
+    bool isLoopIndependent() const { return LoopIndependent; }
+
+    /// isConfused - Returns true if this dependence is confused
+    /// (the compiler understands nothing and makes worst-case
+    /// assumptions).
+    bool isConfused() const { return false; }
+
+    /// isConsistent - Returns true if this dependence is consistent
+    /// (occurs every time the source and destination are executed).
+    bool isConsistent() const { return Consistent; }
+
+    /// getLevels - Returns the number of common loops surrounding the
+    /// souce and destination of the dependence.
+    unsigned getLevels() const { return Levels; }
+
+    /// getDirection - Returns the direction associated with a particular
+    /// level.
+    unsigned getDirection(unsigned Level) const;
+
+    /// getDistance - Returns the distance (or NULL) associated with a
+    /// particular level.
+    const SCEV *getDistance(unsigned Level) const;
+
+    /// isPeelFirst - Returns true if peeling the first iteration from
+    /// this loop will break this dependence.
+    bool isPeelFirst(unsigned Level) const;
+
+    /// isPeelLast - Returns true if peeling the last iteration from
+    /// this loop will break this dependence.
+    bool isPeelLast(unsigned Level) const;
+
+    /// isSplitable - Returns true if splitting the loop will break
+    /// the dependence.
+    bool isSplitable(unsigned Level) const;
+
+    /// isScalar - Returns true if a particular level is scalar; that is,
+    /// if no subscript in the source or destination mention the induction
+    /// variable associated with the loop at this level.
+    bool isScalar(unsigned Level) const;
+  private:
+    unsigned short Levels;
+    bool LoopIndependent;
+    bool Consistent; // Init to true, then refine.
+    DVEntry *DV;
+    friend class DependenceAnalysis;
+  };
+
+
+  /// DependenceAnalysis - This class is the main dependence-analysis driver.
+  ///
+  class DependenceAnalysis : public FunctionPass {
+    void operator=(const DependenceAnalysis &);     // do not implement
+    DependenceAnalysis(const DependenceAnalysis &); // do not implement
+  public:
+    /// depends - Tests for a dependence between the Src and Dst instructions.
+    /// Returns NULL if no dependence; otherwise, returns a Dependence (or a
+    /// FullDependence) with as much information as can be gleaned.
+    /// The flag PossiblyLoopIndependent should be set by the caller
+    /// if it appears that control flow can reach from Src to Dst
+    /// without traversing a loop back edge.
+    Dependence *depends(const Instruction *Src,
+                        const Instruction *Dst,
+                        bool PossiblyLoopIndependent);
+
+    /// getSplitIteration - Give a dependence that's splitable at some
+    /// particular level, return the iteration that should be used to split
+    /// the loop.
+    ///
+    /// Generally, the dependence analyzer will be used to build
+    /// a dependence graph for a function (basically a map from instructions
+    /// to dependences). Looking for cycles in the graph shows us loops
+    /// that cannot be trivially vectorized/parallelized.
+    ///
+    /// We can try to improve the situation by examining all the dependences
+    /// that make up the cycle, looking for ones we can break.
+    /// Sometimes, peeling the first or last iteration of a loop will break
+    /// dependences, and there are flags for those possibilities.
+    /// Sometimes, splitting a loop at some other iteration will do the trick,
+    /// and we've got a flag for that case. Rather than waste the space to
+    /// record the exact iteration (since we rarely know), we provide
+    /// a method that calculates the iteration. It's a drag that it must work
+    /// from scratch, but wonderful in that it's possible.
+    ///
+    /// Here's an example:
+    ///
+    ///    for (i = 0; i < 10; i++)
+    ///        A[i] = ...
+    ///        ... = A[11 - i]
+    ///
+    /// There's a loop-carried flow dependence from the store to the load,
+    /// found by the weak-crossing SIV test. The dependence will have a flag,
+    /// indicating that the dependence can be broken by splitting the loop.
+    /// Calling getSplitIteration will return 5.
+    /// Splitting the loop breaks the dependence, like so:
+    ///
+    ///    for (i = 0; i <= 5; i++)
+    ///        A[i] = ...
+    ///        ... = A[11 - i]
+    ///    for (i = 6; i < 10; i++)
+    ///        A[i] = ...
+    ///        ... = A[11 - i]
+    ///
+    /// breaks the dependence and allows us to vectorize/parallelize
+    /// both loops.
+    const SCEV *getSplitIteration(const Dependence *Dep, unsigned Level);
+
+  private:
+    AliasAnalysis *AA;
+    ScalarEvolution *SE;
+    LoopInfo *LI;
+    Function *F;
+
+    /// Subscript - This private struct represents a pair of subscripts from
+    /// a pair of potentially multi-dimensional array references. We use a
+    /// vector of them to guide subscript partitioning.
+    struct Subscript {
+      const SCEV *Src;
+      const SCEV *Dst;
+      enum ClassificationKind { ZIV, SIV, RDIV, MIV, NonLinear } Classification;
+      SmallBitVector Loops;
+      SmallBitVector GroupLoops;
+      SmallBitVector Group;
+    };
+
+    struct CoefficientInfo {
+      const SCEV *Coeff;
+      const SCEV *PosPart;
+      const SCEV *NegPart;
+      const SCEV *Iterations;
+    };
+
+    struct BoundInfo {
+      const SCEV *Iterations;
+      const SCEV *Upper[8];
+      const SCEV *Lower[8];
+      unsigned char Direction;
+      unsigned char DirSet;
+    };
+
+    /// Constraint - This private class represents a constraint, as defined
+    /// in the paper
+    ///
+    ///           Practical Dependence Testing
+    ///           Goff, Kennedy, Tseng
+    ///           PLDI 1991
+    ///
+    /// There are 5 kinds of constraint, in a hierarchy.
+    ///   1) Any - indicates no constraint, any dependence is possible.
+    ///   2) Line - A line ax + by = c, where a, b, and c are parameters,
+    ///             representing the dependence equation.
+    ///   3) Distance - The value d of the dependence distance;
+    ///   4) Point - A point <x, y> representing the dependence from
+    ///              iteration x to iteration y.
+    ///   5) Empty - No dependence is possible.
+    class Constraint {
+    private:
+      enum ConstraintKind { Empty, Point, Distance, Line, Any } Kind;
+      ScalarEvolution *SE;
+      const SCEV *A;
+      const SCEV *B;
+      const SCEV *C;
+      const Loop *AssociatedLoop;
+    public:
+      /// isEmpty - Return true if the constraint is of kind Empty.
+      bool isEmpty() const { return Kind == Empty; }
+
+      /// isPoint - Return true if the constraint is of kind Point.
+      bool isPoint() const { return Kind == Point; }
+
+      /// isDistance - Return true if the constraint is of kind Distance.
+      bool isDistance() const { return Kind == Distance; }
+
+      /// isLine - Return true if the constraint is of kind Line.
+      /// Since Distance's can also be represented as Lines, we also return
+      /// true if the constraint is of kind Distance.
+      bool isLine() const { return Kind == Line || Kind == Distance; }
+
+      /// isAny - Return true if the constraint is of kind Any;
+      bool isAny() const { return Kind == Any; }
+
+      /// getX - If constraint is a point <X, Y>, returns X.
+      /// Otherwise assert.
+      const SCEV *getX() const;
+
+      /// getY - If constraint is a point <X, Y>, returns Y.
+      /// Otherwise assert.
+      const SCEV *getY() const;
+
+      /// getA - If constraint is a line AX + BY = C, returns A.
+      /// Otherwise assert.
+      const SCEV *getA() const;
+
+      /// getB - If constraint is a line AX + BY = C, returns B.
+      /// Otherwise assert.
+      const SCEV *getB() const;
+
+      /// getC - If constraint is a line AX + BY = C, returns C.
+      /// Otherwise assert.
+      const SCEV *getC() const;
+
+      /// getD - If constraint is a distance, returns D.
+      /// Otherwise assert.
+      const SCEV *getD() const;
+
+      /// getAssociatedLoop - Returns the loop associated with this constraint.
+      const Loop *getAssociatedLoop() const;
+
+      /// setPoint - Change a constraint to Point.
+      void setPoint(const SCEV *X, const SCEV *Y, const Loop *CurrentLoop);
+
+      /// setLine - Change a constraint to Line.
+      void setLine(const SCEV *A, const SCEV *B,
+                   const SCEV *C, const Loop *CurrentLoop);
+
+      /// setDistance - Change a constraint to Distance.
+      void setDistance(const SCEV *D, const Loop *CurrentLoop);
+
+      /// setEmpty - Change a constraint to Empty.
+      void setEmpty();
+
+      /// setAny - Change a constraint to Any.
+      void setAny(ScalarEvolution *SE);
+
+      /// dump - For debugging purposes. Dumps the constraint
+      /// out to OS.
+      void dump(raw_ostream &OS) const;
+    };
+
+
+    /// establishNestingLevels - Examines the loop nesting of the Src and Dst
+    /// instructions and establishes their shared loops. Sets the variables
+    /// CommonLevels, SrcLevels, and MaxLevels.
+    /// The source and destination instructions needn't be contained in the same
+    /// loop. The routine establishNestingLevels finds the level of most deeply
+    /// nested loop that contains them both, CommonLevels. An instruction that's
+    /// not contained in a loop is at level = 0. MaxLevels is equal to the level
+    /// of the source plus the level of the destination, minus CommonLevels.
+    /// This lets us allocate vectors MaxLevels in length, with room for every
+    /// distinct loop referenced in both the source and destination subscripts.
+    /// The variable SrcLevels is the nesting depth of the source instruction.
+    /// It's used to help calculate distinct loops referenced by the destination.
+    /// Here's the map from loops to levels:
+    ///            0 - unused
+    ///            1 - outermost common loop
+    ///          ... - other common loops
+    /// CommonLevels - innermost common loop
+    ///          ... - loops containing Src but not Dst
+    ///    SrcLevels - innermost loop containing Src but not Dst
+    ///          ... - loops containing Dst but not Src
+    ///    MaxLevels - innermost loop containing Dst but not Src
+    /// Consider the follow code fragment:
+    ///    for (a = ...) {
+    ///      for (b = ...) {
+    ///        for (c = ...) {
+    ///          for (d = ...) {
+    ///            A[] = ...;
+    ///          }
+    ///        }
+    ///        for (e = ...) {
+    ///          for (f = ...) {
+    ///            for (g = ...) {
+    ///              ... = A[];
+    ///            }
+    ///          }
+    ///        }
+    ///      }
+    ///    }
+    /// If we're looking at the possibility of a dependence between the store
+    /// to A (the Src) and the load from A (the Dst), we'll note that they
+    /// have 2 loops in common, so CommonLevels will equal 2 and the direction
+    /// vector for Result will have 2 entries. SrcLevels = 4 and MaxLevels = 7.
+    /// A map from loop names to level indices would look like
+    ///     a - 1
+    ///     b - 2 = CommonLevels
+    ///     c - 3
+    ///     d - 4 = SrcLevels
+    ///     e - 5
+    ///     f - 6
+    ///     g - 7 = MaxLevels
+    void establishNestingLevels(const Instruction *Src,
+                                const Instruction *Dst);
+
+    unsigned CommonLevels, SrcLevels, MaxLevels;
+
+    /// mapSrcLoop - Given one of the loops containing the source, return
+    /// its level index in our numbering scheme.
+    unsigned mapSrcLoop(const Loop *SrcLoop) const;
+
+    /// mapDstLoop - Given one of the loops containing the destination,
+    /// return its level index in our numbering scheme.
+    unsigned mapDstLoop(const Loop *DstLoop) const;
+
+    /// isLoopInvariant - Returns true if Expression is loop invariant
+    /// in LoopNest.
+    bool isLoopInvariant(const SCEV *Expression, const Loop *LoopNest) const;
+
+    /// removeMatchingExtensions - Examines a subscript pair.
+    /// If the source and destination are identically sign (or zero)
+    /// extended, it strips off the extension in an effort to
+    /// simplify the actual analysis.
+    void removeMatchingExtensions(Subscript *Pair);
+
+    /// collectCommonLoops - Finds the set of loops from the LoopNest that
+    /// have a level <= CommonLevels and are referred to by the SCEV Expression.
+    void collectCommonLoops(const SCEV *Expression,
+                            const Loop *LoopNest,
+                            SmallBitVector &Loops) const;
+
+    /// checkSrcSubscript - Examines the SCEV Src, returning true iff it's
+    /// linear. Collect the set of loops mentioned by Src.
+    bool checkSrcSubscript(const SCEV *Src,
+                           const Loop *LoopNest,
+                           SmallBitVector &Loops);
+
+    /// checkDstSubscript - Examines the SCEV Dst, returning true iff it's
+    /// linear. Collect the set of loops mentioned by Dst.
+    bool checkDstSubscript(const SCEV *Dst,
+                           const Loop *LoopNest,
+                           SmallBitVector &Loops);
+
+    /// isKnownPredicate - Compare X and Y using the predicate Pred.
+    /// Basically a wrapper for SCEV::isKnownPredicate,
+    /// but tries harder, especially in the presense of sign and zero
+    /// extensions and symbolics.
+    bool isKnownPredicate(ICmpInst::Predicate Pred,
+                          const SCEV *X,
+                          const SCEV *Y) const;
+
+    /// collectUpperBound - All subscripts are the same type (on my machine,
+    /// an i64). The loop bound may be a smaller type. collectUpperBound
+    /// find the bound, if available, and zero extends it to the Type T.
+    /// (I zero extend since the bound should always be >= 0.)
+    /// If no upper bound is available, return NULL.
+    const SCEV *collectUpperBound(const Loop *l, Type *T) const;
+
+    /// collectConstantUpperBound - Calls collectUpperBound(), then
+    /// attempts to cast it to SCEVConstant. If the cast fails,
+    /// returns NULL.
+    const SCEVConstant *collectConstantUpperBound(const Loop *l, Type *T) const;
+
+    /// classifyPair - Examines the subscript pair (the Src and Dst SCEVs)
+    /// and classifies it as either ZIV, SIV, RDIV, MIV, or Nonlinear.
+    /// Collects the associated loops in a set.
+    Subscript::ClassificationKind classifyPair(const SCEV *Src,
+                                           const Loop *SrcLoopNest,
+                                           const SCEV *Dst,
+                                           const Loop *DstLoopNest,
+                                           SmallBitVector &Loops);
+
+    /// testZIV - Tests the ZIV subscript pair (Src and Dst) for dependence.
+    /// Returns true if any possible dependence is disproved.
+    /// If there might be a dependence, returns false.
+    /// If the dependence isn't proven to exist,
+    /// marks the Result as inconsistent.
+    bool testZIV(const SCEV *Src,
+                 const SCEV *Dst,
+                 FullDependence &Result) const;
+
+    /// testSIV - Tests the SIV subscript pair (Src and Dst) for dependence.
+    /// Things of the form [c1 + a1*i] and [c2 + a2*j], where
+    /// i and j are induction variables, c1 and c2 are loop invariant,
+    /// and a1 and a2 are constant.
+    /// Returns true if any possible dependence is disproved.
+    /// If there might be a dependence, returns false.
+    /// Sets appropriate direction vector entry and, when possible,
+    /// the distance vector entry.
+    /// If the dependence isn't proven to exist,
+    /// marks the Result as inconsistent.
+    bool testSIV(const SCEV *Src,
+                 const SCEV *Dst,
+                 unsigned &Level,
+                 FullDependence &Result,
+                 Constraint &NewConstraint,
+                 const SCEV *&SplitIter) const;
+
+    /// testRDIV - Tests the RDIV subscript pair (Src and Dst) for dependence.
+    /// Things of the form [c1 + a1*i] and [c2 + a2*j]
+    /// where i and j are induction variables, c1 and c2 are loop invariant,
+    /// and a1 and a2 are constant.
+    /// With minor algebra, this test can also be used for things like
+    /// [c1 + a1*i + a2*j][c2].
+    /// Returns true if any possible dependence is disproved.
+    /// If there might be a dependence, returns false.
+    /// Marks the Result as inconsistent.
+    bool testRDIV(const SCEV *Src,
+                  const SCEV *Dst,
+                  FullDependence &Result) const;
+
+    /// testMIV - Tests the MIV subscript pair (Src and Dst) for dependence.
+    /// Returns true if dependence disproved.
+    /// Can sometimes refine direction vectors.
+    bool testMIV(const SCEV *Src,
+                 const SCEV *Dst,
+                 const SmallBitVector &Loops,
+                 FullDependence &Result) const;
+
+    /// strongSIVtest - Tests the strong SIV subscript pair (Src and Dst)
+    /// for dependence.
+    /// Things of the form [c1 + a*i] and [c2 + a*i],
+    /// where i is an induction variable, c1 and c2 are loop invariant,
+    /// and a is a constant
+    /// Returns true if any possible dependence is disproved.
+    /// If there might be a dependence, returns false.
+    /// Sets appropriate direction and distance.
+    bool strongSIVtest(const SCEV *Coeff,
+                       const SCEV *SrcConst,
+                       const SCEV *DstConst,
+                       const Loop *CurrentLoop,
+                       unsigned Level,
+                       FullDependence &Result,
+                       Constraint &NewConstraint) const;
+
+    /// weakCrossingSIVtest - Tests the weak-crossing SIV subscript pair
+    /// (Src and Dst) for dependence.
+    /// Things of the form [c1 + a*i] and [c2 - a*i],
+    /// where i is an induction variable, c1 and c2 are loop invariant,
+    /// and a is a constant.
+    /// Returns true if any possible dependence is disproved.
+    /// If there might be a dependence, returns false.
+    /// Sets appropriate direction entry.
+    /// Set consistent to false.
+    /// Marks the dependence as splitable.
+    bool weakCrossingSIVtest(const SCEV *SrcCoeff,
+                             const SCEV *SrcConst,
+                             const SCEV *DstConst,
+                             const Loop *CurrentLoop,
+                             unsigned Level,
+                             FullDependence &Result,
+                             Constraint &NewConstraint,
+                             const SCEV *&SplitIter) const;
+
+    /// ExactSIVtest - Tests the SIV subscript pair
+    /// (Src and Dst) for dependence.
+    /// Things of the form [c1 + a1*i] and [c2 + a2*i],
+    /// where i is an induction variable, c1 and c2 are loop invariant,
+    /// and a1 and a2 are constant.
+    /// Returns true if any possible dependence is disproved.
+    /// If there might be a dependence, returns false.
+    /// Sets appropriate direction entry.
+    /// Set consistent to false.
+    bool exactSIVtest(const SCEV *SrcCoeff,
+                      const SCEV *DstCoeff,
+                      const SCEV *SrcConst,
+                      const SCEV *DstConst,
+                      const Loop *CurrentLoop,
+                      unsigned Level,
+                      FullDependence &Result,
+                      Constraint &NewConstraint) const;
+
+    /// weakZeroSrcSIVtest - Tests the weak-zero SIV subscript pair
+    /// (Src and Dst) for dependence.
+    /// Things of the form [c1] and [c2 + a*i],
+    /// where i is an induction variable, c1 and c2 are loop invariant,
+    /// and a is a constant. See also weakZeroDstSIVtest.
+    /// Returns true if any possible dependence is disproved.
+    /// If there might be a dependence, returns false.
+    /// Sets appropriate direction entry.
+    /// Set consistent to false.
+    /// If loop peeling will break the dependence, mark appropriately.
+    bool weakZeroSrcSIVtest(const SCEV *DstCoeff,
+                            const SCEV *SrcConst,
+                            const SCEV *DstConst,
+                            const Loop *CurrentLoop,
+                            unsigned Level,
+                            FullDependence &Result,
+                            Constraint &NewConstraint) const;
+
+    /// weakZeroDstSIVtest - Tests the weak-zero SIV subscript pair
+    /// (Src and Dst) for dependence.
+    /// Things of the form [c1 + a*i] and [c2],
+    /// where i is an induction variable, c1 and c2 are loop invariant,
+    /// and a is a constant. See also weakZeroSrcSIVtest.
+    /// Returns true if any possible dependence is disproved.
+    /// If there might be a dependence, returns false.
+    /// Sets appropriate direction entry.
+    /// Set consistent to false.
+    /// If loop peeling will break the dependence, mark appropriately.
+    bool weakZeroDstSIVtest(const SCEV *SrcCoeff,
+                            const SCEV *SrcConst,
+                            const SCEV *DstConst,
+                            const Loop *CurrentLoop,
+                            unsigned Level,
+                            FullDependence &Result,
+                            Constraint &NewConstraint) const;
+
+    /// exactRDIVtest - Tests the RDIV subscript pair for dependence.
+    /// Things of the form [c1 + a*i] and [c2 + b*j],
+    /// where i and j are induction variable, c1 and c2 are loop invariant,
+    /// and a and b are constants.
+    /// Returns true if any possible dependence is disproved.
+    /// Marks the result as inconsistant.
+    /// Works in some cases that symbolicRDIVtest doesn't,
+    /// and vice versa.
+    bool exactRDIVtest(const SCEV *SrcCoeff,
+                       const SCEV *DstCoeff,
+                       const SCEV *SrcConst,
+                       const SCEV *DstConst,
+                       const Loop *SrcLoop,
+                       const Loop *DstLoop,
+                       FullDependence &Result) const;
+
+    /// symbolicRDIVtest - Tests the RDIV subscript pair for dependence.
+    /// Things of the form [c1 + a*i] and [c2 + b*j],
+    /// where i and j are induction variable, c1 and c2 are loop invariant,
+    /// and a and b are constants.
+    /// Returns true if any possible dependence is disproved.
+    /// Marks the result as inconsistant.
+    /// Works in some cases that exactRDIVtest doesn't,
+    /// and vice versa. Can also be used as a backup for
+    /// ordinary SIV tests.
+    bool symbolicRDIVtest(const SCEV *SrcCoeff,
+                          const SCEV *DstCoeff,
+                          const SCEV *SrcConst,
+                          const SCEV *DstConst,
+                          const Loop *SrcLoop,
+                          const Loop *DstLoop) const;
+
+    /// gcdMIVtest - Tests an MIV subscript pair for dependence.
+    /// Returns true if any possible dependence is disproved.
+    /// Marks the result as inconsistant.
+    /// Can sometimes disprove the equal direction for 1 or more loops.
+    //  Can handle some symbolics that even the SIV tests don't get,
+    /// so we use it as a backup for everything.
+    bool gcdMIVtest(const SCEV *Src,
+                    const SCEV *Dst,
+                    FullDependence &Result) const;
+
+    /// banerjeeMIVtest - Tests an MIV subscript pair for dependence.
+    /// Returns true if any possible dependence is disproved.
+    /// Marks the result as inconsistant.
+    /// Computes directions.
+    bool banerjeeMIVtest(const SCEV *Src,
+                         const SCEV *Dst,
+                         const SmallBitVector &Loops,
+                         FullDependence &Result) const;
+
+    /// collectCoefficientInfo - Walks through the subscript,
+    /// collecting each coefficient, the associated loop bounds,
+    /// and recording its positive and negative parts for later use.
+    CoefficientInfo *collectCoeffInfo(const SCEV *Subscript,
+                                      bool SrcFlag,
+                                      const SCEV *&Constant) const;
+
+    /// getPositivePart - X^+ = max(X, 0).
+    ///
+    const SCEV *getPositivePart(const SCEV *X) const;
+
+    /// getNegativePart - X^- = min(X, 0).
+    ///
+    const SCEV *getNegativePart(const SCEV *X) const;
+
+    /// getLowerBound - Looks through all the bounds info and
+    /// computes the lower bound given the current direction settings
+    /// at each level.
+    const SCEV *getLowerBound(BoundInfo *Bound) const;
+
+    /// getUpperBound - Looks through all the bounds info and
+    /// computes the upper bound given the current direction settings
+    /// at each level.
+    const SCEV *getUpperBound(BoundInfo *Bound) const;
+
+    /// exploreDirections - Hierarchically expands the direction vector
+    /// search space, combining the directions of discovered dependences
+    /// in the DirSet field of Bound. Returns the number of distinct
+    /// dependences discovered. If the dependence is disproved,
+    /// it will return 0.
+    unsigned exploreDirections(unsigned Level,
+                               CoefficientInfo *A,
+                               CoefficientInfo *B,
+                               BoundInfo *Bound,
+                               const SmallBitVector &Loops,
+                               unsigned &DepthExpanded,
+                               const SCEV *Delta) const;
+
+    /// testBounds - Returns true iff the current bounds are plausible.
+    ///
+    bool testBounds(unsigned char DirKind,
+                    unsigned Level,
+                    BoundInfo *Bound,
+                    const SCEV *Delta) const;
+
+    /// findBoundsALL - Computes the upper and lower bounds for level K
+    /// using the * direction. Records them in Bound.
+    void findBoundsALL(CoefficientInfo *A,
+                       CoefficientInfo *B,
+                       BoundInfo *Bound,
+                       unsigned K) const;
+
+    /// findBoundsLT - Computes the upper and lower bounds for level K
+    /// using the < direction. Records them in Bound.
+    void findBoundsLT(CoefficientInfo *A,
+                      CoefficientInfo *B,
+                      BoundInfo *Bound,
+                      unsigned K) const;
+
+    /// findBoundsGT - Computes the upper and lower bounds for level K
+    /// using the > direction. Records them in Bound.
+    void findBoundsGT(CoefficientInfo *A,
+                      CoefficientInfo *B,
+                      BoundInfo *Bound,
+                      unsigned K) const;
+
+    /// findBoundsEQ - Computes the upper and lower bounds for level K
+    /// using the = direction. Records them in Bound.
+    void findBoundsEQ(CoefficientInfo *A,
+                      CoefficientInfo *B,
+                      BoundInfo *Bound,
+                      unsigned K) const;
+
+    /// intersectConstraints - Updates X with the intersection
+    /// of the Constraints X and Y. Returns true if X has changed.
+    bool intersectConstraints(Constraint *X,
+                              const Constraint *Y);
+
+    /// propagate - Review the constraints, looking for opportunities
+    /// to simplify a subscript pair (Src and Dst).
+    /// Return true if some simplification occurs.
+    /// If the simplification isn't exact (that is, if it is conservative
+    /// in terms of dependence), set consistent to false.
+    bool propagate(const SCEV *&Src,
+                   const SCEV *&Dst,
+                   SmallBitVector &Loops,
+                   SmallVector<Constraint, 4> &Constraints,
+                   bool &Consistent);
+
+    /// propagateDistance - Attempt to propagate a distance
+    /// constraint into a subscript pair (Src and Dst).
+    /// Return true if some simplification occurs.
+    /// If the simplification isn't exact (that is, if it is conservative
+    /// in terms of dependence), set consistent to false.
+    bool propagateDistance(const SCEV *&Src,
+                           const SCEV *&Dst,
+                           Constraint &CurConstraint,
+                           bool &Consistent);
+
+    /// propagatePoint - Attempt to propagate a point
+    /// constraint into a subscript pair (Src and Dst).
+    /// Return true if some simplification occurs.
+    bool propagatePoint(const SCEV *&Src,
+                        const SCEV *&Dst,
+                        Constraint &CurConstraint);
+
+    /// propagateLine - Attempt to propagate a line
+    /// constraint into a subscript pair (Src and Dst).
+    /// Return true if some simplification occurs.
+    /// If the simplification isn't exact (that is, if it is conservative
+    /// in terms of dependence), set consistent to false.
+    bool propagateLine(const SCEV *&Src,
+                       const SCEV *&Dst,
+                       Constraint &CurConstraint,
+                       bool &Consistent);
+
+    /// findCoefficient - Given a linear SCEV,
+    /// return the coefficient corresponding to specified loop.
+    /// If there isn't one, return the SCEV constant 0.
+    /// For example, given a*i + b*j + c*k, returning the coefficient
+    /// corresponding to the j loop would yield b.
+    const SCEV *findCoefficient(const SCEV *Expr,
+                                const Loop *TargetLoop) const;
+
+    /// zeroCoefficient - Given a linear SCEV,
+    /// return the SCEV given by zeroing out the coefficient
+    /// corresponding to the specified loop.
+    /// For example, given a*i + b*j + c*k, zeroing the coefficient
+    /// corresponding to the j loop would yield a*i + c*k.
+    const SCEV *zeroCoefficient(const SCEV *Expr,
+                                const Loop *TargetLoop) const;
+
+    /// addToCoefficient - Given a linear SCEV Expr,
+    /// return the SCEV given by adding some Value to the
+    /// coefficient corresponding to the specified TargetLoop.
+    /// For example, given a*i + b*j + c*k, adding 1 to the coefficient
+    /// corresponding to the j loop would yield a*i + (b+1)*j + c*k.
+    const SCEV *addToCoefficient(const SCEV *Expr,
+                                 const Loop *TargetLoop,
+                                 const SCEV *Value)  const;
+
+    /// updateDirection - Update direction vector entry
+    /// based on the current constraint.
+    void updateDirection(Dependence::DVEntry &Level,
+                         const Constraint &CurConstraint) const;
+  public:
+    static char ID; // Class identification, replacement for typeinfo
+    DependenceAnalysis() : FunctionPass(ID) {
+      initializeDependenceAnalysisPass(*PassRegistry::getPassRegistry());
+    };
+
+    bool runOnFunction(Function &F);
+    void releaseMemory();
+    void getAnalysisUsage(AnalysisUsage &) const;
+    void print(raw_ostream &, const Module * = 0) const;
+  }; // class DependenceAnalysis
+
+  /// createDependenceAnalysisPass - This creates an instance of the
+  /// DependenceAnalysis pass.
+  FunctionPass *createDependenceAnalysisPass();
+
+} // namespace llvm
+
+#endif
diff --git a/include/llvm/Analysis/Passes.h b/include/llvm/Analysis/Passes.h
index c52f846..eddc7c4 100644
--- a/include/llvm/Analysis/Passes.h
+++ b/include/llvm/Analysis/Passes.h
@@ -183,8 +183,17 @@ namespace llvm {
   // createLoopDependenceAnalysisPass - This creates an instance of the
   // LoopDependenceAnalysis pass.
   //
+  LoopPass *createDependenceAnalysisPass();
+
+  //===--------------------------------------------------------------------===//
+  //
+  // createLoopDependenceAnalysisPass - This creates an instance of the
+  // LoopDependenceAnalysis pass.
+  //
   LoopPass *createLoopDependenceAnalysisPass();
 
+  //===--------------------------------------------------------------------===//
+  //
   // Minor pass prototypes, allowing us to expose them through bugpoint and
   // analyze.
   FunctionPass *createInstCountPass();
diff --git a/include/llvm/InitializePasses.h b/include/llvm/InitializePasses.h
index 067d8da..ee9b1c5 100644
--- a/include/llvm/InitializePasses.h
+++ b/include/llvm/InitializePasses.h
@@ -94,6 +94,7 @@ void initializeDCEPass(PassRegistry&);
 void initializeDSEPass(PassRegistry&);
 void initializeDeadInstEliminationPass(PassRegistry&);
 void initializeDeadMachineInstructionElimPass(PassRegistry&);
+void initializeDependenceAnalysisPass(PassRegistry&);
 void initializeDomOnlyPrinterPass(PassRegistry&);
 void initializeDomOnlyViewerPass(PassRegistry&);
 void initializeDomPrinterPass(PassRegistry&);
diff --git a/include/llvm/LinkAllPasses.h b/include/llvm/LinkAllPasses.h
index c01e471..4b10d0e 100644
--- a/include/llvm/LinkAllPasses.h
+++ b/include/llvm/LinkAllPasses.h
@@ -64,6 +64,7 @@ namespace {
       (void) llvm::createDeadCodeEliminationPass();
       (void) llvm::createDeadInstEliminationPass();
       (void) llvm::createDeadStoreEliminationPass();
+      (void) llvm::createDependenceAnalysisPass();
       (void) llvm::createDomOnlyPrinterPass();
       (void) llvm::createDomPrinterPass();
       (void) llvm::createDomOnlyViewerPass();