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[NFC] Promote willNotOverflow() / getStrengthenedNoWrapFlagsFromBinOp() from IndVars into SCEV proper

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We might want to use it when creating SCEV proper in createSCEV(),
now that we don't `forgetValue()` in `SimplifyIndvar::strengthenOverflowingOperation()`,
which might have caused us to loose some optimization potential.
This commit is contained in:
Roman Lebedev 2021-06-01 11:33:52 +03:00
parent cde56bba2d
commit 46218a275e
3 changed files with 104 additions and 66 deletions
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11
include/llvm/Analysis/ScalarEvolution.h
View File

@ -505,6 +505,17 @@ public:
/// Erase Value from ValueExprMap and ExprValueMap.
void eraseValueFromMap(Value *V);
/// Is operation \p BinOp between \p LHS and \p RHS provably does not have
/// a signed/unsigned overflow (\p Signed)?
bool willNotOverflow(Instruction::BinaryOps BinOp, bool Signed,
const SCEV *LHS, const SCEV *RHS);
/// Parse NSW/NUW flags from add/sub/mul IR binary operation \p Op into
/// SCEV no-wrap flags, and deduce flag[s] that aren't known yet.
/// Does not mutate the original instruction.
std::pair<SCEV::NoWrapFlags, bool /*Deduced*/>
getStrengthenedNoWrapFlagsFromBinOp(const OverflowingBinaryOperator *OBO);
/// Return a SCEV expression for the full generality of the specified
/// expression.
const SCEV *getSCEV(Value *V);

75
lib/Analysis/ScalarEvolution.cpp
View File

@ -2244,6 +2244,81 @@ CollectAddOperandsWithScales(DenseMap<const SCEV *, APInt> &M,
return Interesting;
}
bool ScalarEvolution::willNotOverflow(Instruction::BinaryOps BinOp, bool Signed,
const SCEV *LHS, const SCEV *RHS) {
const SCEV *(ScalarEvolution::*Operation)(const SCEV *, const SCEV *,
SCEV::NoWrapFlags, unsigned);
switch (BinOp) {
default:
llvm_unreachable("Unsupported binary op");
case Instruction::Add:
Operation = &ScalarEvolution::getAddExpr;
break;
case Instruction::Sub:
Operation = &ScalarEvolution::getMinusSCEV;
break;
case Instruction::Mul:
Operation = &ScalarEvolution::getMulExpr;
break;
}
const SCEV *(ScalarEvolution::*Extension)(const SCEV *, Type *, unsigned) =
Signed ? &ScalarEvolution::getSignExtendExpr
: &ScalarEvolution::getZeroExtendExpr;
// Check ext(LHS op RHS) == ext(LHS) op ext(RHS)
auto *NarrowTy = cast<IntegerType>(LHS->getType());
auto *WideTy =
IntegerType::get(NarrowTy->getContext(), NarrowTy->getBitWidth() * 2);
const SCEV *A = (this->*Extension)(
(this->*Operation)(LHS, RHS, SCEV::FlagAnyWrap, 0), WideTy, 0);
const SCEV *B = (this->*Operation)((this->*Extension)(LHS, WideTy, 0),
(this->*Extension)(RHS, WideTy, 0),
SCEV::FlagAnyWrap, 0);
return A == B;
}
std::pair<SCEV::NoWrapFlags, bool /*Deduced*/>
ScalarEvolution::getStrengthenedNoWrapFlagsFromBinOp(
const OverflowingBinaryOperator *OBO) {
SCEV::NoWrapFlags Flags = SCEV::NoWrapFlags::FlagAnyWrap;
if (OBO->hasNoUnsignedWrap())
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
if (OBO->hasNoSignedWrap())
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
bool Deduced = false;
if (OBO->hasNoUnsignedWrap() && OBO->hasNoSignedWrap())
return {Flags, Deduced};
if (OBO->getOpcode() != Instruction::Add &&
OBO->getOpcode() != Instruction::Sub &&
OBO->getOpcode() != Instruction::Mul)
return {Flags, Deduced};
const SCEV *LHS = getSCEV(OBO->getOperand(0));
const SCEV *RHS = getSCEV(OBO->getOperand(1));
if (!OBO->hasNoUnsignedWrap() &&
willNotOverflow((Instruction::BinaryOps)OBO->getOpcode(),
/* Signed */ false, LHS, RHS)) {
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNUW);
Deduced = true;
}
if (!OBO->hasNoSignedWrap() &&
willNotOverflow((Instruction::BinaryOps)OBO->getOpcode(),
/* Signed */ true, LHS, RHS)) {
Flags = ScalarEvolution::setFlags(Flags, SCEV::FlagNSW);
Deduced = true;
}
return {Flags, Deduced};
}
// We're trying to construct a SCEV of type `Type' with `Ops' as operands and
// `OldFlags' as can't-wrap behavior. Infer a more aggressive set of
// can't-overflow flags for the operation if possible.

84
lib/Transforms/Utils/SimplifyIndVar.cpp
View File

@ -422,46 +422,10 @@ void SimplifyIndvar::simplifyIVRemainder(BinaryOperator *Rem, Value *IVOperand,
replaceSRemWithURem(Rem);
}
static bool willNotOverflow(ScalarEvolution *SE, Instruction::BinaryOps BinOp,
bool Signed, const SCEV *LHS, const SCEV *RHS) {
const SCEV *(ScalarEvolution::*Operation)(const SCEV *, const SCEV *,
SCEV::NoWrapFlags, unsigned);
switch (BinOp) {
default:
llvm_unreachable("Unsupported binary op");
case Instruction::Add:
Operation = &ScalarEvolution::getAddExpr;
break;
case Instruction::Sub:
Operation = &ScalarEvolution::getMinusSCEV;
break;
case Instruction::Mul:
Operation = &ScalarEvolution::getMulExpr;
break;
}
const SCEV *(ScalarEvolution::*Extension)(const SCEV *, Type *, unsigned) =
Signed ? &ScalarEvolution::getSignExtendExpr
: &ScalarEvolution::getZeroExtendExpr;
// Check ext(LHS op RHS) == ext(LHS) op ext(RHS)
auto *NarrowTy = cast<IntegerType>(LHS->getType());
auto *WideTy =
IntegerType::get(NarrowTy->getContext(), NarrowTy->getBitWidth() * 2);
const SCEV *A =
(SE->*Extension)((SE->*Operation)(LHS, RHS, SCEV::FlagAnyWrap, 0),
WideTy, 0);
const SCEV *B =
(SE->*Operation)((SE->*Extension)(LHS, WideTy, 0),
(SE->*Extension)(RHS, WideTy, 0), SCEV::FlagAnyWrap, 0);
return A == B;
}
bool SimplifyIndvar::eliminateOverflowIntrinsic(WithOverflowInst *WO) {
const SCEV *LHS = SE->getSCEV(WO->getLHS());
const SCEV *RHS = SE->getSCEV(WO->getRHS());
if (!willNotOverflow(SE, WO->getBinaryOp(), WO->isSigned(), LHS, RHS))
if (!SE->willNotOverflow(WO->getBinaryOp(), WO->isSigned(), LHS, RHS))
return false;
// Proved no overflow, nuke the overflow check and, if possible, the overflow
@ -502,7 +466,7 @@ bool SimplifyIndvar::eliminateOverflowIntrinsic(WithOverflowInst *WO) {
bool SimplifyIndvar::eliminateSaturatingIntrinsic(SaturatingInst *SI) {
const SCEV *LHS = SE->getSCEV(SI->getLHS());
const SCEV *RHS = SE->getSCEV(SI->getRHS());
if (!willNotOverflow(SE, SI->getBinaryOp(), SI->isSigned(), LHS, RHS))
if (!SE->willNotOverflow(SI->getBinaryOp(), SI->isSigned(), LHS, RHS))
return false;
BinaryOperator *BO = BinaryOperator::Create(
@ -756,37 +720,25 @@ bool SimplifyIndvar::eliminateIdentitySCEV(Instruction *UseInst,
/// unsigned-overflow. Returns true if anything changed, false otherwise.
bool SimplifyIndvar::strengthenOverflowingOperation(BinaryOperator *BO,
Value *IVOperand) {
// Fastpath: we don't have any work to do if `BO` is `nuw` and `nsw`.
if (BO->hasNoUnsignedWrap() && BO->hasNoSignedWrap())
return false;
SCEV::NoWrapFlags Flags;
bool Deduced;
std::tie(Flags, Deduced) = SE->getStrengthenedNoWrapFlagsFromBinOp(
cast<OverflowingBinaryOperator>(BO));
if (BO->getOpcode() != Instruction::Add &&
BO->getOpcode() != Instruction::Sub &&
BO->getOpcode() != Instruction::Mul)
return false;
if (!Deduced)
return Deduced;
const SCEV *LHS = SE->getSCEV(BO->getOperand(0));
const SCEV *RHS = SE->getSCEV(BO->getOperand(1));
bool Changed = false;
BO->setHasNoUnsignedWrap(ScalarEvolution::maskFlags(Flags, SCEV::FlagNUW) ==
SCEV::FlagNUW);
BO->setHasNoSignedWrap(ScalarEvolution::maskFlags(Flags, SCEV::FlagNSW) ==
SCEV::FlagNSW);
if (!BO->hasNoUnsignedWrap() &&
willNotOverflow(SE, BO->getOpcode(), /* Signed */ false, LHS, RHS)) {
BO->setHasNoUnsignedWrap();
Changed = true;
}
if (!BO->hasNoSignedWrap() &&
willNotOverflow(SE, BO->getOpcode(), /* Signed */ true, LHS, RHS)) {
BO->setHasNoSignedWrap();
Changed = true;
}
// The willNotOverflow() check might infer additional nowrap flags on addrecs
// while performing zero/sign extensions. We could call forgetValue() here
// to make sure those flags also propagate to any other SCEV expressions
// based on the addrec. However, this can have pathological compile-time
// impact, see https://bugs.llvm.org/show_bug.cgi?id=50384.
return Changed;
// The getStrengthenedNoWrapFlagsFromBinOp() check inferred additional nowrap
// flags on addrecs while performing zero/sign extensions. We could call
// forgetValue() here to make sure those flags also propagate to any other
// SCEV expressions based on the addrec. However, this can have pathological
// compile-time impact, see https://bugs.llvm.org/show_bug.cgi?id=50384.
return Deduced;
}
/// Annotate the Shr in (X << IVOperand) >> C as exact using the