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remove BasePointer before delinearizing
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No functional change is intended: instead of relying on the delinearization to
come up with the base pointer as a remainder of the divisions in the
delinearization, we just compute it from the array access and use that value.
We substract the base pointer from the SCEV to be delinearized and that
simplifies the work of the delinearizer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209692 91177308-0d34-0410-b5e6-96231b3b80d8
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Sebastian Pop committed May 27, 2014
1 parent 421b2c5 commit 79facc9
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Showing 4 changed files with 49 additions and 39 deletions.
18 changes: 8 additions & 10 deletions include/llvm/Analysis/ScalarEvolutionExpressions.h
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Original file line number Diff line number Diff line change
Expand Up @@ -362,14 +362,12 @@ namespace llvm {
SmallVectorImpl<const SCEV *> &Terms) const;

/// Return in Subscripts the access functions for each dimension in Sizes.
const SCEV *
computeAccessFunctions(ScalarEvolution &SE,
SmallVectorImpl<const SCEV *> &Subscripts,
SmallVectorImpl<const SCEV *> &Sizes) const;
void computeAccessFunctions(ScalarEvolution &SE,
SmallVectorImpl<const SCEV *> &Subscripts,
SmallVectorImpl<const SCEV *> &Sizes) const;

/// Split this SCEVAddRecExpr into two vectors of SCEVs representing the
/// subscripts and sizes of an array access. Returns the remainder of the
/// delinearization that is the offset start of the array.
/// subscripts and sizes of an array access.
///
/// The delinearization is a 3 step process: the first two steps compute the
/// sizes of each subscript and the third step computes the access functions
Expand Down Expand Up @@ -432,10 +430,10 @@ namespace llvm {
/// The subscript of the outermost dimension is the Quotient: [j+k].
///
/// Overall, we have: A[][n][m], and the access function: A[j+k][2i][5i].
const SCEV *delinearize(ScalarEvolution &SE,
SmallVectorImpl<const SCEV *> &Subscripts,
SmallVectorImpl<const SCEV *> &Sizes,
const SCEV *ElementSize) const;
void delinearize(ScalarEvolution &SE,
SmallVectorImpl<const SCEV *> &Subscripts,
SmallVectorImpl<const SCEV *> &Sizes,
const SCEV *ElementSize) const;
};

//===--------------------------------------------------------------------===//
Expand Down
14 changes: 11 additions & 3 deletions lib/Analysis/Delinearization.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -95,26 +95,34 @@ void Delinearization::print(raw_ostream &O, const Module *) const {
// Do not analyze memory accesses outside loops.
for (Loop *L = LI->getLoopFor(BB); L != nullptr; L = L->getParentLoop()) {
const SCEV *AccessFn = SE->getSCEVAtScope(getPointerOperand(*Inst), L);

const SCEVUnknown *BasePointer =
dyn_cast<SCEVUnknown>(SE->getPointerBase(AccessFn));
// Do not delinearize if we cannot find the base pointer.
if (!BasePointer)
break;
AccessFn = SE->getMinusSCEV(AccessFn, BasePointer);
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(AccessFn);

// Do not try to delinearize memory accesses that are not AddRecs.
if (!AR)
break;


O << "\n";
O << "Inst:" << *Inst << "\n";
O << "In Loop with Header: " << L->getHeader()->getName() << "\n";

O << "AddRec: " << *AR << "\n";

SmallVector<const SCEV *, 3> Subscripts, Sizes;
const SCEV *Res = AR->delinearize(*SE, Subscripts, Sizes, SE->getElementSize(Inst));
AR->delinearize(*SE, Subscripts, Sizes, SE->getElementSize(Inst));
if (Subscripts.size() == 0 || Sizes.size() == 0 ||
Subscripts.size() != Sizes.size()) {
O << "failed to delinearize\n";
continue;
}
O << "Base offset: " << *Res << "\n";

O << "Base offset: " << *BasePointer << "\n";
O << "ArrayDecl[UnknownSize]";
int Size = Subscripts.size();
for (int i = 0; i < Size - 1; i++)
Expand Down
21 changes: 13 additions & 8 deletions lib/Analysis/DependenceAnalysis.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3184,6 +3184,17 @@ bool DependenceAnalysis::tryDelinearize(const SCEV *SrcSCEV,
const SCEV *DstSCEV,
SmallVectorImpl<Subscript> &Pair,
const SCEV *ElementSize) const {
const SCEVUnknown *SrcBase =
dyn_cast<SCEVUnknown>(SE->getPointerBase(SrcSCEV));
const SCEVUnknown *DstBase =
dyn_cast<SCEVUnknown>(SE->getPointerBase(DstSCEV));

if (!SrcBase || !DstBase || SrcBase != DstBase)
return false;

SrcSCEV = SE->getMinusSCEV(SrcSCEV, SrcBase);
DstSCEV = SE->getMinusSCEV(DstSCEV, DstBase);

const SCEVAddRecExpr *SrcAR = dyn_cast<SCEVAddRecExpr>(SrcSCEV);
const SCEVAddRecExpr *DstAR = dyn_cast<SCEVAddRecExpr>(DstSCEV);
if (!SrcAR || !DstAR || !SrcAR->isAffine() || !DstAR->isAffine())
Expand All @@ -3200,20 +3211,14 @@ bool DependenceAnalysis::tryDelinearize(const SCEV *SrcSCEV,

// Third step: compute the access functions for each subscript.
SmallVector<const SCEV *, 4> SrcSubscripts, DstSubscripts;
const SCEV *RemainderS = SrcAR->computeAccessFunctions(*SE, SrcSubscripts, Sizes);
const SCEV *RemainderD = DstAR->computeAccessFunctions(*SE, DstSubscripts, Sizes);
SrcAR->computeAccessFunctions(*SE, SrcSubscripts, Sizes);
DstAR->computeAccessFunctions(*SE, DstSubscripts, Sizes);

// Fail when there is only a subscript: that's a linearized access function.
if (SrcSubscripts.size() < 2 || DstSubscripts.size() < 2 ||
SrcSubscripts.size() != DstSubscripts.size())
return false;

// When the difference in remainders is different than a constant it might be
// that the base address of the arrays is not the same.
const SCEV *DiffRemainders = SE->getMinusSCEV(RemainderS, RemainderD);
if (!isa<SCEVConstant>(DiffRemainders))
return false;

int size = SrcSubscripts.size();

DEBUG({
Expand Down
35 changes: 17 additions & 18 deletions lib/Analysis/ScalarEvolution.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7458,16 +7458,15 @@ void ScalarEvolution::findArrayDimensions(SmallVectorImpl<const SCEV *> &Terms,

/// Third step of delinearization: compute the access functions for the
/// Subscripts based on the dimensions in Sizes.
const SCEV *SCEVAddRecExpr::computeAccessFunctions(
void SCEVAddRecExpr::computeAccessFunctions(
ScalarEvolution &SE, SmallVectorImpl<const SCEV *> &Subscripts,
SmallVectorImpl<const SCEV *> &Sizes) const {

// Early exit in case this SCEV is not an affine multivariate function.
if (Sizes.empty() || !this->isAffine())
return nullptr;
return;

const SCEV *Zero = SE.getConstant(this->getType(), 0);
const SCEV *Res = this, *Remainder = Zero;
const SCEV *Res = this;
int Last = Sizes.size() - 1;
for (int i = Last; i >= 0; i--) {
const SCEV *Q, *R;
Expand All @@ -7488,10 +7487,12 @@ const SCEV *SCEVAddRecExpr::computeAccessFunctions(
if (i == Last) {

// Bail out if the remainder is too complex.
if (isa<SCEVAddRecExpr>(R))
return nullptr;
if (isa<SCEVAddRecExpr>(R)) {
Subscripts.clear();
Sizes.clear();
return;
}

Remainder = R;
continue;
}

Expand All @@ -7510,7 +7511,6 @@ const SCEV *SCEVAddRecExpr::computeAccessFunctions(
for (const SCEV *S : Subscripts)
dbgs() << *S << "\n";
});
return Remainder;
}

/// Splits the SCEV into two vectors of SCEVs representing the subscripts and
Expand Down Expand Up @@ -7562,27 +7562,28 @@ const SCEV *SCEVAddRecExpr::computeAccessFunctions(
/// asking for the SCEV of the memory access with respect to all enclosing
/// loops, calling SCEV->delinearize on that and printing the results.

const SCEV *SCEVAddRecExpr::delinearize(
ScalarEvolution &SE, SmallVectorImpl<const SCEV *> &Subscripts,
SmallVectorImpl<const SCEV *> &Sizes, const SCEV *ElementSize) const {
void SCEVAddRecExpr::delinearize(ScalarEvolution &SE,
SmallVectorImpl<const SCEV *> &Subscripts,
SmallVectorImpl<const SCEV *> &Sizes,
const SCEV *ElementSize) const {
// First step: collect parametric terms.
SmallVector<const SCEV *, 4> Terms;
collectParametricTerms(SE, Terms);

if (Terms.empty())
return nullptr;
return;

// Second step: find subscript sizes.
SE.findArrayDimensions(Terms, Sizes, ElementSize);

if (Sizes.empty())
return nullptr;
return;

// Third step: compute the access functions for each subscript.
const SCEV *Remainder = computeAccessFunctions(SE, Subscripts, Sizes);
computeAccessFunctions(SE, Subscripts, Sizes);

if (!Remainder || Subscripts.empty())
return nullptr;
if (Subscripts.empty())
return;

DEBUG({
dbgs() << "succeeded to delinearize " << *this << "\n";
Expand All @@ -7595,8 +7596,6 @@ const SCEV *SCEVAddRecExpr::delinearize(
dbgs() << "[" << *S << "]";
dbgs() << "\n";
});

return Remainder;
}

//===----------------------------------------------------------------------===//
Expand Down

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