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Add support for reverse pointer induction variables. These are loops that contain pointers that count backwards.

Browse Source 
For example, this is the hot loop in BZIP:

  do {
    m = *--p;
    *p = ( ... );
  } while (--n);



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173219 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nadav Rotem
2013-01-23 01:35:00 +00:00
parent 8246df61f6
commit f148c66ce4
4 changed files with 277 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

89
lib/Transforms/Vectorize/LoopVectorize.cpp
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@ -327,7 +327,8 @@ public:
IK_NoInduction, ///< Not an induction variable.
IK_IntInduction, ///< Integer induction variable. Step = 1.
IK_ReverseIntInduction, ///< Reverse int induction variable. Step = -1.
IK_PtrInduction ///< Pointer induction variable. Step = sizeof(elem).
IK_PtrInduction, ///< Pointer induction var. Step = sizeof(elem).
IK_ReversePtrInduction ///< Reverse ptr indvar. Step = - sizeof(elem).
};
/// This POD struct holds information about reduction variables.
@ -734,6 +735,9 @@ Value *InnerLoopVectorizer::getConsecutiveVector(Value* Val, unsigned StartIdx,
int LoopVectorizationLegality::isConsecutivePtr(Value *Ptr) {
assert(Ptr->getType()->isPointerTy() && "Unexpected non ptr");
// Make sure that the pointer does not point to structs.
if (cast<PointerType>(Ptr->getType())->getElementType()->isAggregateType())
return 0;
// If this value is a pointer induction variable we know it is consecutive.
PHINode *Phi = dyn_cast_or_null<PHINode>(Ptr);
@ -741,6 +745,8 @@ int LoopVectorizationLegality::isConsecutivePtr(Value *Ptr) {
InductionInfo II = Inductions[Phi];
if (IK_PtrInduction == II.IK)
return 1;
else if (IK_ReversePtrInduction == II.IK)
return -1;
}
GetElementPtrInst *Gep = dyn_cast_or_null<GetElementPtrInst>(Ptr);
@ -750,6 +756,29 @@ int LoopVectorizationLegality::isConsecutivePtr(Value *Ptr) {
unsigned NumOperands = Gep->getNumOperands();
Value *LastIndex = Gep->getOperand(NumOperands - 1);
Value *GpPtr = Gep->getPointerOperand();
// If this GEP value is a consecutive pointer induction variable and all of
// the indices are constant then we know it is consecutive. We can
Phi = dyn_cast<PHINode>(GpPtr);
if (Phi && Inductions.count(Phi)) {
// Make sure that the pointer does not point to structs.
PointerType *GepPtrType = cast<PointerType>(GpPtr->getType());
if (GepPtrType->getElementType()->isAggregateType())
return 0;
// Make sure that all of the index operands are loop invariant.
for (unsigned i = 1; i < NumOperands; ++i)
if (!SE->isLoopInvariant(SE->getSCEV(Gep->getOperand(i)), TheLoop))
return 0;
InductionInfo II = Inductions[Phi];
if (IK_PtrInduction == II.IK)
return 1;
else if (IK_ReversePtrInduction == II.IK)
return -1;
}
// Check that all of the gep indices are uniform except for the last.
for (unsigned i = 0; i < NumOperands - 1; ++i)
if (!SE->isLoopInvariant(SE->getSCEV(Gep->getOperand(i)), TheLoop))
@ -1148,6 +1177,18 @@ InnerLoopVectorizer::createEmptyLoop(LoopVectorizationLegality *Legal) {
LoopBypassBlocks.back()->getTerminator());
break;
}
case LoopVectorizationLegality::IK_ReversePtrInduction: {
// The value at the end of the loop for the reverse pointer is calculated
// by creating a GEP with a negative index starting from the start value.
Value *Zero = ConstantInt::get(CountRoundDown->getType(), 0);
Value *NegIdx = BinaryOperator::CreateSub(Zero, CountRoundDown,
"rev.ind.end",
LoopBypassBlocks.back()->getTerminator());
EndValue = GetElementPtrInst::Create(II.StartValue, NegIdx,
"rev.ptr.ind.end",
LoopBypassBlocks.back()->getTerminator());
break;
}
}// end of case
// The new PHI merges the original incoming value, in case of a bypass,
@ -1625,6 +1666,7 @@ InnerLoopVectorizer::vectorizeBlockInLoop(LoopVectorizationLegality *Legal,
}
case LoopVectorizationLegality::IK_ReverseIntInduction:
case LoopVectorizationLegality::IK_PtrInduction:
case LoopVectorizationLegality::IK_ReversePtrInduction:
// Handle reverse integer and pointer inductions.
Value *StartIdx = 0;
// If we have a single integer induction variable then use it.
@ -1660,15 +1702,23 @@ InnerLoopVectorizer::vectorizeBlockInLoop(LoopVectorizationLegality *Legal,
// Handle the pointer induction variable case.
assert(P->getType()->isPointerTy() && "Unexpected type.");
// Is this a reverse induction ptr or a consecutive induction ptr.
bool Reverse = (LoopVectorizationLegality::IK_ReversePtrInduction ==
II.IK);
// This is the vector of results. Notice that we don't generate
// vector geps because scalar geps result in better code.
for (unsigned part = 0; part < UF; ++part) {
Value *VecVal = UndefValue::get(VectorType::get(P->getType(), VF));
for (unsigned int i = 0; i < VF; ++i) {
Constant *Idx = ConstantInt::get(Induction->getType(),
i + part * VF);
Value *GlobalIdx = Builder.CreateAdd(NormalizedIdx, Idx,
"gep.idx");
int EltIndex = (i + part * VF) * (Reverse ? -1 : 1);
Constant *Idx = ConstantInt::get(Induction->getType(), EltIndex);
Value *GlobalIdx;
if (!Reverse)
GlobalIdx = Builder.CreateAdd(NormalizedIdx, Idx, "gep.idx");
else
GlobalIdx = Builder.CreateSub(Idx, NormalizedIdx, "gep.ridx");
Value *SclrGep = Builder.CreateGEP(II.StartValue, GlobalIdx,
"next.gep");
VecVal = Builder.CreateInsertElement(VecVal, SclrGep,
@ -1786,7 +1836,19 @@ InnerLoopVectorizer::vectorizeBlockInLoop(LoopVectorizationLegality *Legal,
// Handle consecutive stores.
GetElementPtrInst *Gep = dyn_cast<GetElementPtrInst>(Ptr);
if (Gep) {
if (Gep && Legal->isInductionVariable(Gep->getPointerOperand())) {
Value *PtrOperand = Gep->getPointerOperand();
Value *FirstBasePtr = getVectorValue(PtrOperand)[0];
FirstBasePtr = Builder.CreateExtractElement(FirstBasePtr, Zero);
// Create the new GEP with the new induction variable.
GetElementPtrInst *Gep2 = cast<GetElementPtrInst>(Gep->clone());
Gep2->setOperand(0, FirstBasePtr);
Ptr = Builder.Insert(Gep2);
} else if (Gep) {
assert(SE->isLoopInvariant(SE->getSCEV(Gep->getPointerOperand()),
OrigLoop) && "Base ptr must be invariant");
// The last index does not have to be the induction. It can be
// consecutive and be a function of the index. For example A[I+1];
unsigned NumOperands = Gep->getNumOperands();
@ -1844,7 +1906,18 @@ InnerLoopVectorizer::vectorizeBlockInLoop(LoopVectorizationLegality *Legal,
}
GetElementPtrInst *Gep = dyn_cast<GetElementPtrInst>(Ptr);
if (Gep) {
if (Gep && Legal->isInductionVariable(Gep->getPointerOperand())) {
Value *PtrOperand = Gep->getPointerOperand();
Value *FirstBasePtr = getVectorValue(PtrOperand)[0];
FirstBasePtr = Builder.CreateExtractElement(FirstBasePtr, Zero);
// Create the new GEP with the new induction variable.
GetElementPtrInst *Gep2 = cast<GetElementPtrInst>(Gep->clone());
Gep2->setOperand(0, FirstBasePtr);
Ptr = Builder.Insert(Gep2);
} else if (Gep) {
assert(SE->isLoopInvariant(SE->getSCEV(Gep->getPointerOperand()),
OrigLoop) && "Base ptr must be invariant");
// The last index does not have to be the induction. It can be
// consecutive and be a function of the index. For example A[I+1];
unsigned NumOperands = Gep->getNumOperands();
@ -2589,6 +2662,8 @@ LoopVectorizationLegality::isInductionVariable(PHINode *Phi) {
uint64_t Size = DL->getTypeAllocSize(PhiTy->getPointerElementType());
if (C->getValue()->equalsInt(Size))
return IK_PtrInduction;
else if (C->getValue()->equalsInt(0 - Size))
return IK_ReversePtrInduction;
return IK_NoInduction;
}