[DA] remove getSplitIteration #167698
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[DA] remove getSplitIteration #167698
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Remove all constraint propagation functions. Simplify depends() and getSplitIteration() to test subscripts individually.
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@llvm/pr-subscribers-llvm-analysis Author: Sebastian Pop (sebpop) ChangesSeparate PR to be committed separately based on top of #160924 Patch is 93.31 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/167698.diff 7 Files Affected:
diff --git a/llvm/include/llvm/Analysis/DependenceAnalysis.h b/llvm/include/llvm/Analysis/DependenceAnalysis.h
index f66c79d915665..ae260cd153177 100644
--- a/llvm/include/llvm/Analysis/DependenceAnalysis.h
+++ b/llvm/include/llvm/Analysis/DependenceAnalysis.h
@@ -302,48 +302,6 @@ class DependenceInfo {
depends(Instruction *Src, Instruction *Dst,
bool UnderRuntimeAssumptions = false);
- /// getSplitIteration - Give a dependence that's splittable 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.
- LLVM_ABI const SCEV *getSplitIteration(const Dependence &Dep, unsigned Level);
-
Function *getFunction() const { return F; }
/// getRuntimeAssumptions - Returns all the runtime assumptions under which
@@ -623,8 +581,7 @@ class DependenceInfo {
/// 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;
+ FullDependence &Result, Constraint &NewConstraint) const;
/// testRDIV - Tests the RDIV subscript pair (Src and Dst) for dependence.
/// Things of the form [c1 + a1*i] and [c2 + a2*j]
@@ -669,8 +626,7 @@ class DependenceInfo {
bool weakCrossingSIVtest(const SCEV *SrcCoeff, const SCEV *SrcConst,
const SCEV *DstConst, const Loop *CurrentLoop,
unsigned Level, FullDependence &Result,
- Constraint &NewConstraint,
- const SCEV *&SplitIter) const;
+ Constraint &NewConstraint) const;
/// ExactSIVtest - Tests the SIV subscript pair
/// (Src and Dst) for dependence.
@@ -838,35 +794,6 @@ class DependenceInfo {
/// 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,
- SmallVectorImpl<Constraint> &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.
diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp
index da86a8d2cc9c0..c9ecc936424c3 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -73,8 +73,6 @@ using namespace llvm;
// statistics
STATISTIC(TotalArrayPairs, "Array pairs tested");
-STATISTIC(SeparableSubscriptPairs, "Separable subscript pairs");
-STATISTIC(CoupledSubscriptPairs, "Coupled subscript pairs");
STATISTIC(NonlinearSubscriptPairs, "Nonlinear subscript pairs");
STATISTIC(ZIVapplications, "ZIV applications");
STATISTIC(ZIVindependence, "ZIV independence");
@@ -96,8 +94,6 @@ STATISTIC(SymbolicRDIVapplications, "Symbolic RDIV applications");
STATISTIC(SymbolicRDIVindependence, "Symbolic RDIV independence");
STATISTIC(DeltaApplications, "Delta applications");
STATISTIC(DeltaSuccesses, "Delta successes");
-STATISTIC(DeltaIndependence, "Delta independence");
-STATISTIC(DeltaPropagations, "Delta propagations");
STATISTIC(GCDapplications, "GCD applications");
STATISTIC(GCDsuccesses, "GCD successes");
STATISTIC(GCDindependence, "GCD independence");
@@ -208,7 +204,6 @@ static void dumpExampleDependence(raw_ostream &OS, DependenceInfo *DA,
for (unsigned Level = 1; Level <= D->getLevels(); Level++) {
if (D->isSplitable(Level)) {
OS << " da analyze - split level = " << Level;
- OS << ", iteration = " << *DA->getSplitIteration(*D, Level);
OS << "!\n";
}
}
@@ -1351,10 +1346,12 @@ bool DependenceInfo::strongSIVtest(const SCEV *Coeff, const SCEV *SrcConst,
// Can determine iteration for splitting.
//
// Return true if dependence disproved.
-bool DependenceInfo::weakCrossingSIVtest(
- const SCEV *Coeff, const SCEV *SrcConst, const SCEV *DstConst,
- const Loop *CurLoop, unsigned Level, FullDependence &Result,
- Constraint &NewConstraint, const SCEV *&SplitIter) const {
+bool DependenceInfo::weakCrossingSIVtest(const SCEV *Coeff,
+ const SCEV *SrcConst,
+ const SCEV *DstConst,
+ const Loop *CurLoop, unsigned Level,
+ FullDependence &Result,
+ Constraint &NewConstraint) const {
LLVM_DEBUG(dbgs() << "\tWeak-Crossing SIV test\n");
LLVM_DEBUG(dbgs() << "\t Coeff = " << *Coeff << "\n");
LLVM_DEBUG(dbgs() << "\t SrcConst = " << *SrcConst << "\n");
@@ -1390,12 +1387,6 @@ bool DependenceInfo::weakCrossingSIVtest(
}
assert(SE->isKnownPositive(ConstCoeff) && "ConstCoeff should be positive");
- // compute SplitIter for use by DependenceInfo::getSplitIteration()
- SplitIter = SE->getUDivExpr(
- SE->getSMaxExpr(SE->getZero(Delta->getType()), Delta),
- SE->getMulExpr(SE->getConstant(Delta->getType(), 2), ConstCoeff));
- LLVM_DEBUG(dbgs() << "\t Split iter = " << *SplitIter << "\n");
-
const SCEVConstant *ConstDelta = dyn_cast<SCEVConstant>(Delta);
if (!ConstDelta)
return false;
@@ -2232,8 +2223,8 @@ bool DependenceInfo::symbolicRDIVtest(const SCEV *A1, const SCEV *A2,
//
// Return true if dependence disproved.
bool DependenceInfo::testSIV(const SCEV *Src, const SCEV *Dst, unsigned &Level,
- FullDependence &Result, Constraint &NewConstraint,
- const SCEV *&SplitIter) const {
+ FullDependence &Result,
+ Constraint &NewConstraint) const {
LLVM_DEBUG(dbgs() << " src = " << *Src << "\n");
LLVM_DEBUG(dbgs() << " dst = " << *Dst << "\n");
const SCEVAddRecExpr *SrcAddRec = dyn_cast<SCEVAddRecExpr>(Src);
@@ -2253,7 +2244,7 @@ bool DependenceInfo::testSIV(const SCEV *Src, const SCEV *Dst, unsigned &Level,
Result, NewConstraint);
else if (SrcCoeff == SE->getNegativeSCEV(DstCoeff))
disproven = weakCrossingSIVtest(SrcCoeff, SrcConst, DstConst, CurLoop,
- Level, Result, NewConstraint, SplitIter);
+ Level, Result, NewConstraint);
else
disproven = exactSIVtest(SrcCoeff, DstCoeff, SrcConst, DstConst, CurLoop,
Level, Result, NewConstraint);
@@ -3116,153 +3107,8 @@ const SCEV *DependenceInfo::addToCoefficient(const SCEV *Expr,
AddRec->getNoWrapFlags());
}
-// 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.
-// Corresponds to Figure 5 from the paper
-//
-// Practical Dependence Testing
-// Goff, Kennedy, Tseng
-// PLDI 1991
-bool DependenceInfo::propagate(const SCEV *&Src, const SCEV *&Dst,
- SmallBitVector &Loops,
- SmallVectorImpl<Constraint> &Constraints,
- bool &Consistent) {
- bool Result = false;
- for (unsigned LI : Loops.set_bits()) {
- LLVM_DEBUG(dbgs() << "\t Constraint[" << LI << "] is");
- LLVM_DEBUG(Constraints[LI].dump(dbgs()));
- if (Constraints[LI].isDistance())
- Result |= propagateDistance(Src, Dst, Constraints[LI], Consistent);
- else if (Constraints[LI].isLine())
- Result |= propagateLine(Src, Dst, Constraints[LI], Consistent);
- else if (Constraints[LI].isPoint())
- Result |= propagatePoint(Src, Dst, Constraints[LI]);
- }
- return Result;
-}
-// 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 DependenceInfo::propagateDistance(const SCEV *&Src, const SCEV *&Dst,
- Constraint &CurConstraint,
- bool &Consistent) {
- const Loop *CurLoop = CurConstraint.getAssociatedLoop();
- LLVM_DEBUG(dbgs() << "\t\tSrc is " << *Src << "\n");
- const SCEV *A_K = findCoefficient(Src, CurLoop);
- if (A_K->isZero())
- return false;
- const SCEV *DA_K = SE->getMulExpr(A_K, CurConstraint.getD());
- Src = SE->getMinusSCEV(Src, DA_K);
- Src = zeroCoefficient(Src, CurLoop);
- LLVM_DEBUG(dbgs() << "\t\tnew Src is " << *Src << "\n");
- LLVM_DEBUG(dbgs() << "\t\tDst is " << *Dst << "\n");
- Dst = addToCoefficient(Dst, CurLoop, SE->getNegativeSCEV(A_K));
- LLVM_DEBUG(dbgs() << "\t\tnew Dst is " << *Dst << "\n");
- if (!findCoefficient(Dst, CurLoop)->isZero())
- Consistent = false;
- return true;
-}
-// 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 DependenceInfo::propagateLine(const SCEV *&Src, const SCEV *&Dst,
- Constraint &CurConstraint,
- bool &Consistent) {
- const Loop *CurLoop = CurConstraint.getAssociatedLoop();
- const SCEV *A = CurConstraint.getA();
- const SCEV *B = CurConstraint.getB();
- const SCEV *C = CurConstraint.getC();
- LLVM_DEBUG(dbgs() << "\t\tA = " << *A << ", B = " << *B << ", C = " << *C
- << "\n");
- LLVM_DEBUG(dbgs() << "\t\tSrc = " << *Src << "\n");
- LLVM_DEBUG(dbgs() << "\t\tDst = " << *Dst << "\n");
- if (A->isZero()) {
- const SCEVConstant *Bconst = dyn_cast<SCEVConstant>(B);
- const SCEVConstant *Cconst = dyn_cast<SCEVConstant>(C);
- if (!Bconst || !Cconst)
- return false;
- APInt Beta = Bconst->getAPInt();
- APInt Charlie = Cconst->getAPInt();
- APInt CdivB = Charlie.sdiv(Beta);
- assert(Charlie.srem(Beta) == 0 && "C should be evenly divisible by B");
- const SCEV *AP_K = findCoefficient(Dst, CurLoop);
- Src = SE->getMinusSCEV(Src, SE->getMulExpr(AP_K, SE->getConstant(CdivB)));
- Dst = zeroCoefficient(Dst, CurLoop);
- if (!findCoefficient(Src, CurLoop)->isZero())
- Consistent = false;
- } else if (B->isZero()) {
- const SCEVConstant *Aconst = dyn_cast<SCEVConstant>(A);
- const SCEVConstant *Cconst = dyn_cast<SCEVConstant>(C);
- if (!Aconst || !Cconst)
- return false;
- APInt Alpha = Aconst->getAPInt();
- APInt Charlie = Cconst->getAPInt();
- APInt CdivA = Charlie.sdiv(Alpha);
- assert(Charlie.srem(Alpha) == 0 && "C should be evenly divisible by A");
- const SCEV *A_K = findCoefficient(Src, CurLoop);
- Src = SE->getAddExpr(Src, SE->getMulExpr(A_K, SE->getConstant(CdivA)));
- Src = zeroCoefficient(Src, CurLoop);
- if (!findCoefficient(Dst, CurLoop)->isZero())
- Consistent = false;
- } else if (isKnownPredicate(CmpInst::ICMP_EQ, A, B)) {
- const SCEVConstant *Aconst = dyn_cast<SCEVConstant>(A);
- const SCEVConstant *Cconst = dyn_cast<SCEVConstant>(C);
- if (!Aconst || !Cconst)
- return false;
- APInt Alpha = Aconst->getAPInt();
- APInt Charlie = Cconst->getAPInt();
- APInt CdivA = Charlie.sdiv(Alpha);
- assert(Charlie.srem(Alpha) == 0 && "C should be evenly divisible by A");
- const SCEV *A_K = findCoefficient(Src, CurLoop);
- Src = SE->getAddExpr(Src, SE->getMulExpr(A_K, SE->getConstant(CdivA)));
- Src = zeroCoefficient(Src, CurLoop);
- Dst = addToCoefficient(Dst, CurLoop, A_K);
- if (!findCoefficient(Dst, CurLoop)->isZero())
- Consistent = false;
- } else {
- // paper is incorrect here, or perhaps just misleading
- const SCEV *A_K = findCoefficient(Src, CurLoop);
- Src = SE->getMulExpr(Src, A);
- Dst = SE->getMulExpr(Dst, A);
- Src = SE->getAddExpr(Src, SE->getMulExpr(A_K, C));
- Src = zeroCoefficient(Src, CurLoop);
- Dst = addToCoefficient(Dst, CurLoop, SE->getMulExpr(A_K, B));
- if (!findCoefficient(Dst, CurLoop)->isZero())
- Consistent = false;
- }
- LLVM_DEBUG(dbgs() << "\t\tnew Src = " << *Src << "\n");
- LLVM_DEBUG(dbgs() << "\t\tnew Dst = " << *Dst << "\n");
- return true;
-}
-
-// Attempt to propagate a point
-// constraint into a subscript pair (Src and Dst).
-// Return true if some simplification occurs.
-bool DependenceInfo::propagatePoint(const SCEV *&Src, const SCEV *&Dst,
- Constraint &CurConstraint) {
- const Loop *CurLoop = CurConstraint.getAssociatedLoop();
- const SCEV *A_K = findCoefficient(Src, CurLoop);
- const SCEV *AP_K = findCoefficient(Dst, CurLoop);
- const SCEV *XA_K = SE->getMulExpr(A_K, CurConstraint.getX());
- const SCEV *YAP_K = SE->getMulExpr(AP_K, CurConstraint.getY());
- LLVM_DEBUG(dbgs() << "\t\tSrc is " << *Src << "\n");
- Src = SE->getAddExpr(Src, SE->getMinusSCEV(XA_K, YAP_K));
- Src = zeroCoefficient(Src, CurLoop);
- LLVM_DEBUG(dbgs() << "\t\tnew Src is " << *Src << "\n");
- LLVM_DEBUG(dbgs() << "\t\tDst is " << *Dst << "\n");
- Dst = zeroCoefficient(Dst, CurLoop);
- LLVM_DEBUG(dbgs() << "\t\tnew Dst is " << *Dst << "\n");
- return true;
-}
// Update direction vector entry based on the current constraint.
void DependenceInfo::updateDirection(Dependence::DVEntry &Level,
@@ -3579,8 +3425,6 @@ SCEVUnionPredicate DependenceInfo::getRuntimeAssumptions() const {
// Goff, Kennedy, Tseng
// PLDI 1991
//
-// Care is required to keep the routine below, getSplitIteration(),
-// up to date with respect to this routine.
std::unique_ptr<Dependence>
DependenceInfo::depends(Instruction *Src, Instruction *Dst,
bool UnderRuntimeAssumptions) {
@@ -3726,68 +3570,11 @@ DependenceInfo::depends(Instruction *Src, Instruction *Dst,
LLVM_DEBUG(dumpSmallBitVector(Pair[P].Loops));
}
- SmallBitVector Separable(Pairs);
- SmallBitVector Coupled(Pairs);
-
- // Partition subscripts into separable and minimally-coupled groups
- // Algorithm in paper is algorithmically better;
- // this may be faster in practice. Check someday.
- //
- // Here's an example of how it works. Consider this code:
- //
- // for (i = ...) {
- // for (j = ...) {
- // for (k = ...) {
- // for (l = ...) {
- // for (m = ...) {
- // A[i][j][k][m] = ...;
- // ... = A[0][j][l][i + j];
- // }
- // }
- // }
- // }
- // }
- //
- // There are 4 subscripts here:
- // 0 [i] and [0]
- // 1 [j] and [j]
- // 2 [k] and [l]
- // 3 [m] and [i + j]
- //
- // We've already classified each subscript pair as ZIV, SIV, etc.,
- // and collected all the loops mentioned by pair P in Pair[P].Loops.
- // In addition, we've initialized Pair[P].GroupLoops to Pair[P].Loops
- // and set Pair[P].Group = {P}.
- //
- // Src Dst Classification Loops GroupLoops Group
- // 0 [i] [0] SIV {1} {1} {0}
- // 1 [j] [j] SIV {2} {2} {1}
- // 2 [k] [l] RDIV {3,4} {3,4} {2}
- // 3 [m] [i + j] MIV {1,2,5} {1,2,5} {3}
- //
- // For each subscript SI 0 .. 3, we consider each remaining subscript, SJ.
- // So, 0 is compared against 1, 2, and 3; 1 is compared against 2 and 3, etc.
- //
- // We begin by comparing 0 and 1. The intersection of the GroupLoops is empty.
- // Next, 0 and 2. Again, the intersection of their GroupLoops is empty.
- // Next 0 and 3. The intersection of their GroupLoop = {1}, not empty,
- // so Pair[3].Group = {0,3} and Done = false (that is, 0 will not be added
- // to either Separable or Coupled).
- //
- // Next, we consider 1 and 2. The intersection of the GroupLoops is empty.
- // Next, 1 and 3. The intersection of their GroupLoops = {2}, not empty,
- // so Pair[3].Group = {0, 1, 3} and Done = false.
- //
- // Next, we compare 2 against 3. The intersection of the GroupLoops is empty.
- // Since Done remains true, we add 2 to the set of Separable pairs.
- //
- // Finally, we consider 3. There's nothing to compare it with,
- // so Done remains true and we add it to the Coupled set.
- // Pair[3].Group = {0, 1, 3} and GroupLoops = {1, 2, 5}.
- //
- // In the end, we've got 1 separable subscript and 1 coupled group.
+ // Test each subscript individually
for (unsigned SI = 0; SI < Pairs; ++SI) {
- if (Pair[SI].Classification == Subscript::NonLinear) {
+ LLVM_DEBUG(dbgs() << "testing subscript " << SI);
+ switch (Pair[SI].Classification) {
+ case Subscript::NonLinear:
// ignore these, but collect loops for later
++NonlinearSubscriptPairs;
collectCommonLoops(Pair[SI].Src, LI->getLoopFor(Src->getParent()),
@@ -3795,47 +3582,7 @@ DependenceInfo::depends(Instruction *Src, Instruction *Dst,
collectCommonLoops(Pair[SI].Dst, LI->getLoopFor(Dst->getParent()),
Pair[SI].Loops);
Result.Consistent = false;
- } ...
[truncated]
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Separate PR to be committed separately based on top of #160924