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[DependenceAnalysis] Extending SIV to handle separate loops #128782

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ede8ec2
[DependenceAnalysis] Extending SIV to handle separate loops
1997alireza Feb 24, 2025
21ef00f
[NFC] Applying clang-format
1997alireza May 29, 2025
7466249
[LoopFusion] Detecting loop-carried dependencies using DA info
1997alireza May 30, 2025
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205 changes: 136 additions & 69 deletions llvm/include/llvm/Analysis/DependenceAnalysis.h
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Original file line number Diff line number Diff line change
Expand Up @@ -82,6 +82,17 @@ namespace llvm {
/// Dependence::DVEntry - Each level in the distance/direction vector
/// has a direction (or perhaps a union of several directions), and
/// perhaps a distance.
/// The dependency information could be across a single loop level or across
/// two separate levels that are similar. Two levels are considered similar
/// if they can be interpreted as a single fused loop, i.e., have the same
/// trip count and the same nesting depth.
/// For example, loops b and c are similar and considered as separate loops:
/// for (a = ...) {
/// for (b = 0; b < 10; b++) {
/// }
/// for (c = 0; c < 10; c++) {
/// }
/// }
struct DVEntry {
enum : unsigned char {
NONE = 0,
Expand Down Expand Up @@ -153,13 +164,26 @@ namespace llvm {
/// source and destination of the dependence.
virtual unsigned getLevels() const { return 0; }

/// getSeparateLevels - Returns the number of separate loops surrounding
/// the source and destination of the dependence.
virtual unsigned getSeparateLevels() const { return 0; }

/// getDVEntry - Returns the DV entry associated with a regular or a
/// separate level
DVEntry getDVEntry(unsigned Level, bool Separate) const;

/// getDirection - Returns the direction associated with a particular
/// level.
virtual unsigned getDirection(unsigned Level) const { return DVEntry::ALL; }
/// common or separate level.
virtual unsigned getDirection(unsigned Level, bool Separate = false) const {
return DVEntry::ALL;
}

/// getDistance - Returns the distance (or NULL) associated with a
/// particular level.
virtual const SCEV *getDistance(unsigned Level) const { return nullptr; }
/// particular common or separate level.
virtual const SCEV *getDistance(unsigned Level,
bool Separate = false) const {
return nullptr;
}

/// Check if the direction vector is negative. A negative direction
/// vector means Src and Dst are reversed in the actual program.
Expand All @@ -172,21 +196,31 @@ namespace llvm {
virtual bool normalize(ScalarEvolution *SE) { return false; }

/// isPeelFirst - Returns true if peeling the first iteration from
/// this loop will break this dependence.
virtual bool isPeelFirst(unsigned Level) const { return false; }
/// this regular or separate loop level will break this dependence.
virtual bool isPeelFirst(unsigned Level, bool Separate = false) 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; }
/// this regular or separate loop level will break this dependence.
virtual bool isPeelLast(unsigned Level, bool Separate = false) const {
return false;
}

/// isSplitable - Returns true if splitting this loop will break
/// isSplitable - Returns true if splitting the loop will break
/// the dependence.
virtual bool isSplitable(unsigned Level) const { return false; }
virtual bool isSplitable(unsigned Level, bool Separate = false) const {
return false;
}

/// inSeparateLoops - Returns true if this level is a separate level, i.e.,
/// performed across two separate loop nests.
virtual bool inSeparateLoops(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;
/// isScalar - Returns true if a particular regular or separate 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, bool Separate = false) const;

/// getNextPredecessor - Returns the value of the NextPredecessor
/// field.
Expand All @@ -212,6 +246,10 @@ namespace llvm {
///
void dump(raw_ostream &OS) const;

/// dumpImp - For debugging purposes. Dumps a dependence to OS with or
/// without considering the separate levels.
void dumpImp(raw_ostream &OS, bool Separate = false) const;

protected:
Instruction *Src, *Dst;

Expand Down Expand Up @@ -252,13 +290,31 @@ namespace llvm {
/// source and destination of the dependence.
unsigned getLevels() const override { return Levels; }

/// getSeparateLevels - Returns the number of separate loops surrounding
/// the source and destination of the dependence.
unsigned getSeparateLevels() const override { return SeparateLevels; }

/// getDVEntry - Returns the DV entry associated with a regular or a
/// separate level
DVEntry getDVEntry(unsigned Level, bool Separate) const {
if (!Separate) {
assert(0 < Level && Level <= Levels && "Level out of range");
return DV[Level - 1];
} else {
assert(Levels < Level && Level <= Levels + SeparateLevels &&
"Separate level out of range");
return DVSeparate[Level - Levels - 1];
}
}

/// getDirection - Returns the direction associated with a particular
/// level.
unsigned getDirection(unsigned Level) const override;
/// common or separate level.
unsigned getDirection(unsigned Level, bool Separate = false) const override;

/// getDistance - Returns the distance (or NULL) associated with a
/// particular level.
const SCEV *getDistance(unsigned Level) const override;
/// particular common or separate level.
const SCEV *getDistance(unsigned Level,
bool Separate = false) const override;

/// Check if the direction vector is negative. A negative direction
/// vector means Src and Dst are reversed in the actual program.
Expand All @@ -271,27 +327,33 @@ namespace llvm {
bool normalize(ScalarEvolution *SE) override;

/// isPeelFirst - Returns true if peeling the first iteration from
/// this loop will break this dependence.
bool isPeelFirst(unsigned Level) const override;
/// this regular or separate loop level will break this dependence.
bool isPeelFirst(unsigned Level, bool Separate = false) const override;

/// isPeelLast - Returns true if peeling the last iteration from
/// this loop will break this dependence.
bool isPeelLast(unsigned Level) const override;
/// this regular or separate loop level will break this dependence.
bool isPeelLast(unsigned Level, bool Separate = false) const override;

/// isSplitable - Returns true if splitting the loop will break
/// the dependence.
bool isSplitable(unsigned Level) const override;
bool isSplitable(unsigned Level, bool Separate = false) const override;

/// 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 override;
/// inSeparateLoops - Returns true if this level is a separate level, i.e.,
/// performed across two separate loop nests.
bool inSeparateLoops(unsigned Level) const override;

/// isScalar - Returns true if a particular regular or separate 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, bool Separate = false) const override;

private:
unsigned short Levels;
unsigned short SeparateLevels;
bool LoopIndependent;
bool Consistent; // Init to true, then refine.
std::unique_ptr<DVEntry[]> DV;
std::unique_ptr<DVEntry[]> DVSeparate;
friend class DependenceInfo;
};

Expand Down Expand Up @@ -423,7 +485,8 @@ namespace llvm {
const SCEV *A;
const SCEV *B;
const SCEV *C;
const Loop *AssociatedLoop;
const Loop *AssociatedSrcLoop;
const Loop *AssociatedDstLoop;

public:
/// isEmpty - Return true if the constraint is of kind Empty.
Expand Down Expand Up @@ -467,19 +530,27 @@ namespace llvm {
/// Otherwise assert.
LLVM_ABI const SCEV *getD() const;

/// getAssociatedLoop - Returns the loop associated with this constraint.
LLVM_ABI const Loop *getAssociatedLoop() const;
/// getAssociatedSrcLoop - Returns the source loop associated with this
/// constraint.
LLVM_ABI const Loop *getAssociatedSrcLoop() const;

/// getAssociatedDstLoop - Returns the destination loop associated with
/// this constraint.
LLVM_ABI const Loop *getAssociatedDstLoop() const;

/// setPoint - Change a constraint to Point.
LLVM_ABI void setPoint(const SCEV *X, const SCEV *Y,
const Loop *CurrentLoop);
const Loop *CurrentSrcLoop,
const Loop *CurrentDstLoop);

/// setLine - Change a constraint to Line.
LLVM_ABI void setLine(const SCEV *A, const SCEV *B, const SCEV *C,
const Loop *CurrentLoop);
const Loop *CurrentSrcLoop,
const Loop *CurrentDstLoop);

/// setDistance - Change a constraint to Distance.
LLVM_ABI void setDistance(const SCEV *D, const Loop *CurrentLoop);
LLVM_ABI void setDistance(const SCEV *D, const Loop *CurrentSrcLoop,
const Loop *CurrentDstLoop);

/// setEmpty - Change a constraint to Empty.
LLVM_ABI void setEmpty();
Expand All @@ -492,6 +563,10 @@ namespace llvm {
LLVM_ABI void dump(raw_ostream &OS) const;
};

/// Returns true if two loops are the same or they have the same tripcount
/// and depth
bool areLoopsSimilar(const Loop *SrcLoop, const Loop *DstLoop) const;

/// establishNestingLevels - Examines the loop nesting of the Src and Dst
/// instructions and establishes their shared loops. Sets the variables
/// CommonLevels, SrcLevels, and MaxLevels.
Expand All @@ -503,8 +578,8 @@ namespace llvm {
/// 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:
/// It's used to help calculate distinct loops referenced by the
/// destination. Here's the map from loops to levels:
Comment on lines +581 to +582
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[nit] Please avoid unelated changes

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Fixed.

/// 0 - unused
/// 1 - outermost common loop
/// ... - other common loops
Expand Down Expand Up @@ -542,10 +617,15 @@ namespace llvm {
/// e - 5
/// f - 6
/// g - 7 = MaxLevels
void establishNestingLevels(const Instruction *Src,
const Instruction *Dst);
/// SeparateLevels counts the number of loop levels after the common levels
/// that are not identical but are considered similar. Two levels are
/// considered similar if they have the same trip count and the same
/// nesting depth.
/// For example, if loops `c` and `e` are similar, then they contribute to
/// the SeparateLevels count and SeparateLevels is set to 1.
Comment on lines +620 to +625
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Not messing up with the level count is a good thing.

void establishNestingLevels(const Instruction *Src, const Instruction *Dst);

unsigned CommonLevels, SrcLevels, MaxLevels;
unsigned CommonLevels, SrcLevels, MaxLevels, SeparateLevels;

/// mapSrcLoop - Given one of the loops containing the source, return
/// its level index in our numbering scheme.
Expand Down Expand Up @@ -684,13 +764,10 @@ namespace llvm {
/// 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;
bool strongSIVtest(const SCEV *Coeff, const SCEV *SrcConst,
const SCEV *DstConst, const Loop *CurrentSrcLoop,
const Loop *CurrentDstLoop, unsigned Level,
FullDependence &Result, Constraint &NewConstraint) const;

/// weakCrossingSIVtest - Tests the weak-crossing SIV subscript pair
/// (Src and Dst) for dependence.
Expand All @@ -702,13 +779,10 @@ namespace llvm {
/// 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,
bool weakCrossingSIVtest(const SCEV *SrcCoeff, const SCEV *SrcConst,
const SCEV *DstConst, const Loop *CurrentSrcLoop,
const Loop *CurrentDstLoop, unsigned Level,
FullDependence &Result, Constraint &NewConstraint,
const SCEV *&SplitIter) const;

/// ExactSIVtest - Tests the SIV subscript pair
Expand All @@ -720,13 +794,10 @@ namespace llvm {
/// 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,
bool exactSIVtest(const SCEV *SrcCoeff, const SCEV *DstCoeff,
const SCEV *SrcConst, const SCEV *DstConst,
const Loop *CurrentSrcLoop, const Loop *CurrentDstLoop,
unsigned Level, FullDependence &Result,
Constraint &NewConstraint) const;

/// weakZeroSrcSIVtest - Tests the weak-zero SIV subscript pair
Expand All @@ -739,11 +810,9 @@ namespace llvm {
/// 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,
bool weakZeroSrcSIVtest(const SCEV *DstCoeff, const SCEV *SrcConst,
const SCEV *DstConst, const Loop *CurrentSrcLoop,
const Loop *CurrentDstLoop, unsigned Level,
FullDependence &Result,
Constraint &NewConstraint) const;

Expand All @@ -757,11 +826,9 @@ namespace llvm {
/// 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,
bool weakZeroDstSIVtest(const SCEV *SrcCoeff, const SCEV *SrcConst,
const SCEV *DstConst, const Loop *CurrentSrcLoop,
const Loop *CurrentDstLoop, unsigned Level,
FullDependence &Result,
Constraint &NewConstraint) const;

Expand Down
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