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[VectorCombine] refactor cost calcs to reduce duplication; NFC 

More cleanup is possible now, but we probably need to
resolve the TODO about the existing difference between
compares and binops.
This commit is contained in:
Sanjay Patel 2020-02-21 14:25:39 -05:00
parent e2ed1d14d6
commit 34e3485560
1 changed files with 85 additions and 76 deletions
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137
llvm/lib/Transforms/Vectorize/VectorCombine.cpp
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@ -33,6 +33,68 @@ using namespace llvm::PatternMatch;
STATISTIC(NumVecCmp, "Number of vector compares formed");
STATISTIC(NumVecBO, "Number of vector binops formed");
/// Compare the relative costs of extracts followed by scalar operation vs.
/// vector operation followed by extract:
/// opcode (extelt V0, C), (extelt V1, C) --> extelt (opcode V0, V1), C
/// Unless the vector op is much more expensive than the scalar op, this
/// eliminates an extract.
static bool isExtractExtractCheap(Instruction *Ext0, Instruction *Ext1,
unsigned Opcode,
const TargetTransformInfo &TTI) {
assert(Ext0->getOperand(1) == Ext1->getOperand(1) &&
isa<ConstantInt>(Ext0->getOperand(1)) &&
"Expected same constant extract index");
Type *ScalarTy = Ext0->getType();
Type *VecTy = Ext0->getOperand(0)->getType();
int ScalarOpCost, VectorOpCost;
// Get cost estimates for scalar and vector versions of the operation.
bool IsBinOp = Instruction::isBinaryOp(Opcode);
if (IsBinOp) {
ScalarOpCost = TTI.getArithmeticInstrCost(Opcode, ScalarTy);
VectorOpCost = TTI.getArithmeticInstrCost(Opcode, VecTy);
} else {
assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) &&
"Expected a compare");
ScalarOpCost = TTI.getCmpSelInstrCost(Opcode, ScalarTy,
CmpInst::makeCmpResultType(ScalarTy));
VectorOpCost = TTI.getCmpSelInstrCost(Opcode, VecTy,
CmpInst::makeCmpResultType(VecTy));
}
// Get cost estimate for the extract element. This cost will factor into
// both sequences.
unsigned ExtIndex = cast<ConstantInt>(Ext0->getOperand(1))->getZExtValue();
int ExtractCost = TTI.getVectorInstrCost(Instruction::ExtractElement,
VecTy, ExtIndex);
// Extra uses of the extracts mean that we include those costs in the
// vector total because those instructions will not be eliminated.
int ScalarCost, VectorCost;
if (Ext0->getOperand(0) == Ext1->getOperand(0)) {
// Handle a special case. If the 2 operands are identical, adjust the
// formulas to account for that. The extra use charge allows for either the
// CSE'd pattern or an unoptimized form with identical values:
// opcode (extelt V, C), (extelt V, C) --> extelt (opcode V, V), C
bool HasUseTax = Ext0 == Ext1 ? !Ext0->hasNUses(2)
: !Ext0->hasOneUse() || !Ext1->hasOneUse();
ScalarCost = ExtractCost + ScalarOpCost;
VectorCost = VectorOpCost + ExtractCost + HasUseTax * ExtractCost;
} else {
// Handle the general case. Each extract is actually a different value:
// opcode (extelt V0, C), (extelt V1, C) --> extelt (opcode V0, V1), C
ScalarCost = 2 * ExtractCost + ScalarOpCost;
VectorCost = VectorOpCost + ExtractCost +
!Ext0->hasOneUse() * ExtractCost +
!Ext1->hasOneUse() * ExtractCost;
}
// TODO: The cost comparison should not differ based on opcode. Either we
// want to be uniformly more or less aggressive in deciding if a vector
// operation should replace the scalar operation.
return IsBinOp ? ScalarCost <= VectorCost : ScalarCost < VectorCost;
}
/// Try to reduce extract element costs by converting scalar compares to vector
/// compares followed by extract.
/// cmp (ext0 V0, C0), (ext1 V1, C1)
@ -40,37 +102,20 @@ static bool foldExtExtCmp(Instruction *Ext0, Value *V0, uint64_t C0,
Instruction *Ext1, Value *V1, uint64_t C1,
Instruction &I, const TargetTransformInfo &TTI) {
assert(isa<CmpInst>(&I) && "Expected a compare");
Type *ScalarTy = Ext0->getType();
Type *VecTy = V0->getType();
bool IsFP = ScalarTy->isFloatingPointTy();
unsigned CmpOpcode = IsFP ? Instruction::FCmp : Instruction::ICmp;
// TODO: Handle C0 != C1 by shuffling 1 of the operands.
if (C0 != C1)
return false;
// Check if the existing scalar code or the vector alternative is cheaper.
// Extra uses of the extracts mean that we include those costs in the
// vector total because those instructions will not be eliminated.
// ((2 * extract) + scalar cmp) < (vector cmp + extract) ?
int ExtractCost =
TTI.getVectorInstrCost(Instruction::ExtractElement, VecTy, C0);
int ScalarCmpCost = TTI.getCmpSelInstrCost(CmpOpcode, ScalarTy, I.getType());
int VecCmpCost = TTI.getCmpSelInstrCost(CmpOpcode, VecTy,
CmpInst::makeCmpResultType(VecTy));
int ScalarCost = 2 * ExtractCost + ScalarCmpCost;
int VecCost = VecCmpCost + ExtractCost +
!Ext0->hasOneUse() * ExtractCost +
!Ext1->hasOneUse() * ExtractCost;
if (ScalarCost < VecCost)
if (isExtractExtractCheap(Ext0, Ext1, I.getOpcode(), TTI))
return false;
// cmp Pred (extelt V0, C), (extelt V1, C) --> extelt (cmp Pred V0, V1), C
++NumVecCmp;
IRBuilder<> Builder(&I);
CmpInst::Predicate Pred = cast<CmpInst>(&I)->getPredicate();
Value *VecCmp = IsFP ? Builder.CreateFCmp(Pred, V0, V1)
Value *VecCmp =
Ext0->getType()->isFloatingPointTy() ? Builder.CreateFCmp(Pred, V0, V1)
: Builder.CreateICmp(Pred, V0, V1);
Value *Extract = Builder.CreateExtractElement(VecCmp, Ext0->getOperand(1));
I.replaceAllUsesWith(Extract);
@ -84,51 +129,19 @@ static bool foldExtExtBinop(Instruction *Ext0, Value *V0, uint64_t C0,
Instruction *Ext1, Value *V1, uint64_t C1,
Instruction &I, const TargetTransformInfo &TTI) {
assert(isa<BinaryOperator>(&I) && "Expected a binary operator");
Type *ScalarTy = Ext0->getType();
Type *VecTy = V0->getType();
Instruction::BinaryOps BOpcode = cast<BinaryOperator>(I).getOpcode();
// Check if using a vector binop would be cheaper.
int ScalarBOCost = TTI.getArithmeticInstrCost(BOpcode, ScalarTy);
int VecBOCost = TTI.getArithmeticInstrCost(BOpcode, VecTy);
int Extract0Cost = TTI.getVectorInstrCost(Instruction::ExtractElement,
VecTy, C0);
// Handle a special case - if the extract indexes are the same, the
// replacement sequence does not require a shuffle. Unless the vector binop is
// much more expensive than the scalar binop, this eliminates an extract.
// Extra uses of the extracts mean that we include those costs in the
// vector total because those instructions will not be eliminated.
if (C0 == C1) {
assert(Extract0Cost ==
TTI.getVectorInstrCost(Instruction::ExtractElement, VecTy, C1) &&
"Different costs for same extract?");
int ExtractCost = Extract0Cost;
if (V0 != V1) {
int ScalarCost = ExtractCost + ExtractCost + ScalarBOCost;
int VecCost = VecBOCost + ExtractCost +
!Ext0->hasOneUse() * ExtractCost +
!Ext1->hasOneUse() * ExtractCost;
if (ScalarCost <= VecCost)
// TODO: Handle C0 != C1 by shuffling 1 of the operands.
if (C0 != C1)
return false;
} else {
// Handle an extra-special case. If the 2 binop operands are identical,
// adjust the formulas to account for that:
// bo (extelt V, C), (extelt V, C) --> extelt (bo V, V), C
// The extra use charge allows for either the CSE'd pattern or an
// unoptimized form with identical values.
bool HasUseTax = Ext0 == Ext1 ? !Ext0->hasNUses(2)
: !Ext0->hasOneUse() || !Ext1->hasOneUse();
int ScalarCost = ExtractCost + ScalarBOCost;
int VecCost = VecBOCost + ExtractCost + HasUseTax * ExtractCost;
if (ScalarCost <= VecCost)
return false;
}
// bo (extelt X, C), (extelt Y, C) --> extelt (bo X, Y), C
if (isExtractExtractCheap(Ext0, Ext1, I.getOpcode(), TTI))
return false;
// bo (extelt V0, C), (extelt V1, C) --> extelt (bo V0, V1), C
++NumVecBO;
IRBuilder<> Builder(&I);
Value *NewBO = Builder.CreateBinOp(BOpcode, V0, V1);
Value *NewBO =
Builder.CreateBinOp(cast<BinaryOperator>(&I)->getOpcode(), V0, V1);
if (auto *VecBOInst = dyn_cast<Instruction>(NewBO)) {
// All IR flags are safe to back-propagate because any potential poison
// created in unused vector elements is discarded by the extract.
@ -137,10 +150,6 @@ static bool foldExtExtBinop(Instruction *Ext0, Value *V0, uint64_t C0,
Value *Extract = Builder.CreateExtractElement(NewBO, Ext0->getOperand(1));
I.replaceAllUsesWith(Extract);
return true;
}
// TODO: Handle C0 != C1 by shuffling 1 of the operands.
return false;
}
/// Match an instruction with extracted vector operands.