llvm-project/polly/lib/Support/SCEVValidator.cpp

704 lines
21 KiB
C++

#include "polly/Support/SCEVValidator.h"
#include "polly/ScopInfo.h"
#include "llvm/Analysis/RegionInfo.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Support/Debug.h"
#include <vector>
using namespace llvm;
using namespace polly;
#define DEBUG_TYPE "polly-scev-validator"
namespace SCEVType {
/// @brief The type of a SCEV
///
/// To check for the validity of a SCEV we assign to each SCEV a type. The
/// possible types are INT, PARAM, IV and INVALID. The order of the types is
/// important. The subexpressions of SCEV with a type X can only have a type
/// that is smaller or equal than X.
enum TYPE {
// An integer value.
INT,
// An expression that is constant during the execution of the Scop,
// but that may depend on parameters unknown at compile time.
PARAM,
// An expression that may change during the execution of the SCoP.
IV,
// An invalid expression.
INVALID
};
}
/// @brief The result the validator returns for a SCEV expression.
class ValidatorResult {
/// @brief The type of the expression
SCEVType::TYPE Type;
/// @brief The set of Parameters in the expression.
std::vector<const SCEV *> Parameters;
public:
/// @brief The copy constructor
ValidatorResult(const ValidatorResult &Source) {
Type = Source.Type;
Parameters = Source.Parameters;
}
/// @brief Construct a result with a certain type and no parameters.
ValidatorResult(SCEVType::TYPE Type) : Type(Type) {
assert(Type != SCEVType::PARAM && "Did you forget to pass the parameter");
}
/// @brief Construct a result with a certain type and a single parameter.
ValidatorResult(SCEVType::TYPE Type, const SCEV *Expr) : Type(Type) {
Parameters.push_back(Expr);
}
/// @brief Get the type of the ValidatorResult.
SCEVType::TYPE getType() { return Type; }
/// @brief Is the analyzed SCEV constant during the execution of the SCoP.
bool isConstant() { return Type == SCEVType::INT || Type == SCEVType::PARAM; }
/// @brief Is the analyzed SCEV valid.
bool isValid() { return Type != SCEVType::INVALID; }
/// @brief Is the analyzed SCEV of Type IV.
bool isIV() { return Type == SCEVType::IV; }
/// @brief Is the analyzed SCEV of Type INT.
bool isINT() { return Type == SCEVType::INT; }
/// @brief Is the analyzed SCEV of Type PARAM.
bool isPARAM() { return Type == SCEVType::PARAM; }
/// @brief Get the parameters of this validator result.
std::vector<const SCEV *> getParameters() { return Parameters; }
/// @brief Add the parameters of Source to this result.
void addParamsFrom(const ValidatorResult &Source) {
Parameters.insert(Parameters.end(), Source.Parameters.begin(),
Source.Parameters.end());
}
/// @brief Merge a result.
///
/// This means to merge the parameters and to set the Type to the most
/// specific Type that matches both.
void merge(const ValidatorResult &ToMerge) {
Type = std::max(Type, ToMerge.Type);
addParamsFrom(ToMerge);
}
void print(raw_ostream &OS) {
switch (Type) {
case SCEVType::INT:
OS << "SCEVType::INT";
break;
case SCEVType::PARAM:
OS << "SCEVType::PARAM";
break;
case SCEVType::IV:
OS << "SCEVType::IV";
break;
case SCEVType::INVALID:
OS << "SCEVType::INVALID";
break;
}
}
};
raw_ostream &operator<<(raw_ostream &OS, class ValidatorResult &VR) {
VR.print(OS);
return OS;
}
/// Check if a SCEV is valid in a SCoP.
struct SCEVValidator
: public SCEVVisitor<SCEVValidator, class ValidatorResult> {
private:
const Region *R;
Loop *Scope;
ScalarEvolution &SE;
const Value *BaseAddress;
InvariantLoadsSetTy *ILS;
public:
SCEVValidator(const Region *R, Loop *Scope, ScalarEvolution &SE,
const Value *BaseAddress, InvariantLoadsSetTy *ILS)
: R(R), Scope(Scope), SE(SE), BaseAddress(BaseAddress), ILS(ILS) {}
class ValidatorResult visitConstant(const SCEVConstant *Constant) {
return ValidatorResult(SCEVType::INT);
}
class ValidatorResult visitTruncateExpr(const SCEVTruncateExpr *Expr) {
ValidatorResult Op = visit(Expr->getOperand());
switch (Op.getType()) {
case SCEVType::INT:
case SCEVType::PARAM:
// We currently do not represent a truncate expression as an affine
// expression. If it is constant during Scop execution, we treat it as a
// parameter.
return ValidatorResult(SCEVType::PARAM, Expr);
case SCEVType::IV:
DEBUG(dbgs() << "INVALID: Truncation of SCEVType::IV expression");
return ValidatorResult(SCEVType::INVALID);
case SCEVType::INVALID:
return Op;
}
llvm_unreachable("Unknown SCEVType");
}
class ValidatorResult visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) {
ValidatorResult Op = visit(Expr->getOperand());
switch (Op.getType()) {
case SCEVType::INT:
case SCEVType::PARAM:
// We currently do not represent a truncate expression as an affine
// expression. If it is constant during Scop execution, we treat it as a
// parameter.
return ValidatorResult(SCEVType::PARAM, Expr);
case SCEVType::IV:
DEBUG(dbgs() << "INVALID: ZeroExtend of SCEVType::IV expression");
return ValidatorResult(SCEVType::INVALID);
case SCEVType::INVALID:
return Op;
}
llvm_unreachable("Unknown SCEVType");
}
class ValidatorResult visitSignExtendExpr(const SCEVSignExtendExpr *Expr) {
// We currently allow only signed SCEV expressions. In the case of a
// signed value, a sign extend is a noop.
//
// TODO: Reconsider this when we add support for unsigned values.
return visit(Expr->getOperand());
}
class ValidatorResult visitAddExpr(const SCEVAddExpr *Expr) {
ValidatorResult Return(SCEVType::INT);
for (int i = 0, e = Expr->getNumOperands(); i < e; ++i) {
ValidatorResult Op = visit(Expr->getOperand(i));
Return.merge(Op);
// Early exit.
if (!Return.isValid())
break;
}
// TODO: Check for NSW and NUW.
return Return;
}
class ValidatorResult visitMulExpr(const SCEVMulExpr *Expr) {
ValidatorResult Return(SCEVType::INT);
bool HasMultipleParams = false;
for (int i = 0, e = Expr->getNumOperands(); i < e; ++i) {
ValidatorResult Op = visit(Expr->getOperand(i));
if (Op.isINT())
continue;
if (Op.isPARAM() && Return.isPARAM()) {
HasMultipleParams = true;
continue;
}
if ((Op.isIV() || Op.isPARAM()) && !Return.isINT()) {
DEBUG(dbgs() << "INVALID: More than one non-int operand in MulExpr\n"
<< "\tExpr: " << *Expr << "\n"
<< "\tPrevious expression type: " << Return << "\n"
<< "\tNext operand (" << Op
<< "): " << *Expr->getOperand(i) << "\n");
return ValidatorResult(SCEVType::INVALID);
}
Return.merge(Op);
}
if (HasMultipleParams && Return.isValid())
return ValidatorResult(SCEVType::PARAM, Expr);
// TODO: Check for NSW and NUW.
return Return;
}
class ValidatorResult visitUDivExpr(const SCEVUDivExpr *Expr) {
ValidatorResult LHS = visit(Expr->getLHS());
ValidatorResult RHS = visit(Expr->getRHS());
// We currently do not represent an unsigned division as an affine
// expression. If the division is constant during Scop execution we treat it
// as a parameter, otherwise we bail out.
if (LHS.isConstant() && RHS.isConstant())
return ValidatorResult(SCEVType::PARAM, Expr);
DEBUG(dbgs() << "INVALID: unsigned division of non-constant expressions");
return ValidatorResult(SCEVType::INVALID);
}
class ValidatorResult visitAddRecExpr(const SCEVAddRecExpr *Expr) {
if (!Expr->isAffine()) {
DEBUG(dbgs() << "INVALID: AddRec is not affine");
return ValidatorResult(SCEVType::INVALID);
}
ValidatorResult Start = visit(Expr->getStart());
ValidatorResult Recurrence = visit(Expr->getStepRecurrence(SE));
if (!Start.isValid())
return Start;
if (!Recurrence.isValid())
return Recurrence;
auto *L = Expr->getLoop();
if (R->contains(L) && (!Scope || !L->contains(Scope))) {
DEBUG(dbgs() << "INVALID: AddRec out of a loop whose exit value is not "
"synthesizable");
return ValidatorResult(SCEVType::INVALID);
}
if (R->contains(L)) {
if (Recurrence.isINT()) {
ValidatorResult Result(SCEVType::IV);
Result.addParamsFrom(Start);
return Result;
}
DEBUG(dbgs() << "INVALID: AddRec within scop has non-int"
"recurrence part");
return ValidatorResult(SCEVType::INVALID);
}
assert(Start.isConstant() && Recurrence.isConstant() &&
"Expected 'Start' and 'Recurrence' to be constant");
// Directly generate ValidatorResult for Expr if 'start' is zero.
if (Expr->getStart()->isZero())
return ValidatorResult(SCEVType::PARAM, Expr);
// Translate AddRecExpr from '{start, +, inc}' into 'start + {0, +, inc}'
// if 'start' is not zero.
const SCEV *ZeroStartExpr = SE.getAddRecExpr(
SE.getConstant(Expr->getStart()->getType(), 0),
Expr->getStepRecurrence(SE), Expr->getLoop(), Expr->getNoWrapFlags());
ValidatorResult ZeroStartResult =
ValidatorResult(SCEVType::PARAM, ZeroStartExpr);
ZeroStartResult.addParamsFrom(Start);
return ZeroStartResult;
}
class ValidatorResult visitSMaxExpr(const SCEVSMaxExpr *Expr) {
ValidatorResult Return(SCEVType::INT);
for (int i = 0, e = Expr->getNumOperands(); i < e; ++i) {
ValidatorResult Op = visit(Expr->getOperand(i));
if (!Op.isValid())
return Op;
Return.merge(Op);
}
return Return;
}
class ValidatorResult visitUMaxExpr(const SCEVUMaxExpr *Expr) {
// We do not support unsigned operations. If 'Expr' is constant during Scop
// execution we treat this as a parameter, otherwise we bail out.
for (int i = 0, e = Expr->getNumOperands(); i < e; ++i) {
ValidatorResult Op = visit(Expr->getOperand(i));
if (!Op.isConstant()) {
DEBUG(dbgs() << "INVALID: UMaxExpr has a non-constant operand");
return ValidatorResult(SCEVType::INVALID);
}
}
return ValidatorResult(SCEVType::PARAM, Expr);
}
ValidatorResult visitGenericInst(Instruction *I, const SCEV *S) {
if (R->contains(I)) {
DEBUG(dbgs() << "INVALID: UnknownExpr references an instruction "
"within the region\n");
return ValidatorResult(SCEVType::INVALID);
}
return ValidatorResult(SCEVType::PARAM, S);
}
ValidatorResult visitLoadInstruction(Instruction *I, const SCEV *S) {
if (R->contains(I) && ILS) {
ILS->insert(cast<LoadInst>(I));
return ValidatorResult(SCEVType::PARAM, S);
}
return visitGenericInst(I, S);
}
ValidatorResult visitSDivInstruction(Instruction *SDiv, const SCEV *S) {
assert(SDiv->getOpcode() == Instruction::SDiv &&
"Assumed SDiv instruction!");
auto *Divisor = SDiv->getOperand(1);
auto *CI = dyn_cast<ConstantInt>(Divisor);
if (!CI)
return visitGenericInst(SDiv, S);
auto *Dividend = SDiv->getOperand(0);
auto *DividendSCEV = SE.getSCEV(Dividend);
return visit(DividendSCEV);
}
ValidatorResult visitSRemInstruction(Instruction *SRem, const SCEV *S) {
assert(SRem->getOpcode() == Instruction::SRem &&
"Assumed SRem instruction!");
auto *Divisor = SRem->getOperand(1);
auto *CI = dyn_cast<ConstantInt>(Divisor);
if (!CI)
return visitGenericInst(SRem, S);
auto *Dividend = SRem->getOperand(0);
auto *DividendSCEV = SE.getSCEV(Dividend);
return visit(DividendSCEV);
}
ValidatorResult visitUnknown(const SCEVUnknown *Expr) {
Value *V = Expr->getValue();
// TODO: FIXME: IslExprBuilder is not capable of producing valid code
// for arbitrary pointer expressions at the moment. Until
// this is fixed we disallow pointer expressions completely.
if (Expr->getType()->isPointerTy()) {
DEBUG(dbgs() << "INVALID: UnknownExpr is a pointer type [FIXME]");
return ValidatorResult(SCEVType::INVALID);
}
if (!Expr->getType()->isIntegerTy()) {
DEBUG(dbgs() << "INVALID: UnknownExpr is not an integer");
return ValidatorResult(SCEVType::INVALID);
}
if (isa<UndefValue>(V)) {
DEBUG(dbgs() << "INVALID: UnknownExpr references an undef value");
return ValidatorResult(SCEVType::INVALID);
}
if (BaseAddress == V) {
DEBUG(dbgs() << "INVALID: UnknownExpr references BaseAddress\n");
return ValidatorResult(SCEVType::INVALID);
}
if (Instruction *I = dyn_cast<Instruction>(Expr->getValue())) {
switch (I->getOpcode()) {
case Instruction::Load:
return visitLoadInstruction(I, Expr);
case Instruction::SDiv:
return visitSDivInstruction(I, Expr);
case Instruction::SRem:
return visitSRemInstruction(I, Expr);
default:
return visitGenericInst(I, Expr);
}
}
return ValidatorResult(SCEVType::PARAM, Expr);
}
};
/// @brief Check whether a SCEV refers to an SSA name defined inside a region.
///
struct SCEVInRegionDependences
: public SCEVVisitor<SCEVInRegionDependences, bool> {
public:
/// Returns true when the SCEV has SSA names defined in region R. It @p
/// AllowLoops is false, loop dependences are checked as well. AddRec SCEVs
/// are only allowed within its loop (current loop determined by @p Scope),
/// not outside of it unless AddRec's loop is not even in the region.
static bool hasDependences(const SCEV *S, const Region *R, Loop *Scope,
bool AllowLoops) {
SCEVInRegionDependences Ignore(R, Scope, AllowLoops);
return Ignore.visit(S);
}
SCEVInRegionDependences(const Region *R, Loop *Scope, bool AllowLoops)
: R(R), Scope(Scope), AllowLoops(AllowLoops) {}
bool visit(const SCEV *Expr) {
return SCEVVisitor<SCEVInRegionDependences, bool>::visit(Expr);
}
bool visitConstant(const SCEVConstant *Constant) { return false; }
bool visitTruncateExpr(const SCEVTruncateExpr *Expr) {
return visit(Expr->getOperand());
}
bool visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) {
return visit(Expr->getOperand());
}
bool visitSignExtendExpr(const SCEVSignExtendExpr *Expr) {
return visit(Expr->getOperand());
}
bool visitAddExpr(const SCEVAddExpr *Expr) {
for (int i = 0, e = Expr->getNumOperands(); i < e; ++i)
if (visit(Expr->getOperand(i)))
return true;
return false;
}
bool visitMulExpr(const SCEVMulExpr *Expr) {
for (int i = 0, e = Expr->getNumOperands(); i < e; ++i)
if (visit(Expr->getOperand(i)))
return true;
return false;
}
bool visitUDivExpr(const SCEVUDivExpr *Expr) {
if (visit(Expr->getLHS()))
return true;
if (visit(Expr->getRHS()))
return true;
return false;
}
bool visitAddRecExpr(const SCEVAddRecExpr *Expr) {
if (!AllowLoops) {
if (!Scope)
return true;
auto *L = Expr->getLoop();
if (R->contains(L) && !L->contains(Scope))
return true;
}
for (size_t i = 0; i < Expr->getNumOperands(); ++i)
if (visit(Expr->getOperand(i)))
return true;
return false;
}
bool visitSMaxExpr(const SCEVSMaxExpr *Expr) {
for (size_t i = 0; i < Expr->getNumOperands(); ++i)
if (visit(Expr->getOperand(i)))
return true;
return false;
}
bool visitUMaxExpr(const SCEVUMaxExpr *Expr) {
for (size_t i = 0; i < Expr->getNumOperands(); ++i)
if (visit(Expr->getOperand(i)))
return true;
return false;
}
bool visitUnknown(const SCEVUnknown *Expr) {
Instruction *Inst = dyn_cast<Instruction>(Expr->getValue());
// Return true when Inst is defined inside the region R.
if (Inst && R->contains(Inst))
return true;
return false;
}
private:
const Region *R;
Loop *Scope;
bool AllowLoops;
};
namespace polly {
/// Find all loops referenced in SCEVAddRecExprs.
class SCEVFindLoops {
SetVector<const Loop *> &Loops;
public:
SCEVFindLoops(SetVector<const Loop *> &Loops) : Loops(Loops) {}
bool follow(const SCEV *S) {
if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(S))
Loops.insert(AddRec->getLoop());
return true;
}
bool isDone() { return false; }
};
void findLoops(const SCEV *Expr, SetVector<const Loop *> &Loops) {
SCEVFindLoops FindLoops(Loops);
SCEVTraversal<SCEVFindLoops> ST(FindLoops);
ST.visitAll(Expr);
}
/// Find all values referenced in SCEVUnknowns.
class SCEVFindValues {
SetVector<Value *> &Values;
public:
SCEVFindValues(SetVector<Value *> &Values) : Values(Values) {}
bool follow(const SCEV *S) {
if (const SCEVUnknown *Unknown = dyn_cast<SCEVUnknown>(S))
Values.insert(Unknown->getValue());
return true;
}
bool isDone() { return false; }
};
void findValues(const SCEV *Expr, SetVector<Value *> &Values) {
SCEVFindValues FindValues(Values);
SCEVTraversal<SCEVFindValues> ST(FindValues);
ST.visitAll(Expr);
}
bool hasScalarDepsInsideRegion(const SCEV *Expr, const Region *R,
llvm::Loop *Scope, bool AllowLoops) {
return SCEVInRegionDependences::hasDependences(Expr, R, Scope, AllowLoops);
}
bool isAffineExpr(const Region *R, llvm::Loop *Scope, const SCEV *Expr,
ScalarEvolution &SE, const Value *BaseAddress,
InvariantLoadsSetTy *ILS) {
if (isa<SCEVCouldNotCompute>(Expr))
return false;
SCEVValidator Validator(R, Scope, SE, BaseAddress, ILS);
DEBUG({
dbgs() << "\n";
dbgs() << "Expr: " << *Expr << "\n";
dbgs() << "Region: " << R->getNameStr() << "\n";
dbgs() << " -> ";
});
ValidatorResult Result = Validator.visit(Expr);
DEBUG({
if (Result.isValid())
dbgs() << "VALID\n";
dbgs() << "\n";
});
return Result.isValid();
}
static bool isAffineParamExpr(Value *V, const Region *R, Loop *Scope,
ScalarEvolution &SE,
std::vector<const SCEV *> &Params) {
auto *E = SE.getSCEV(V);
if (isa<SCEVCouldNotCompute>(E))
return false;
SCEVValidator Validator(R, Scope, SE, nullptr, nullptr);
ValidatorResult Result = Validator.visit(E);
if (!Result.isConstant())
return false;
auto ResultParams = Result.getParameters();
Params.insert(Params.end(), ResultParams.begin(), ResultParams.end());
return true;
}
bool isAffineParamConstraint(Value *V, const Region *R, llvm::Loop *Scope,
ScalarEvolution &SE,
std::vector<const SCEV *> &Params, bool OrExpr) {
if (auto *ICmp = dyn_cast<ICmpInst>(V)) {
return isAffineParamConstraint(ICmp->getOperand(0), R, Scope, SE, Params,
true) &&
isAffineParamConstraint(ICmp->getOperand(1), R, Scope, SE, Params,
true);
} else if (auto *BinOp = dyn_cast<BinaryOperator>(V)) {
auto Opcode = BinOp->getOpcode();
if (Opcode == Instruction::And || Opcode == Instruction::Or)
return isAffineParamConstraint(BinOp->getOperand(0), R, Scope, SE, Params,
false) &&
isAffineParamConstraint(BinOp->getOperand(1), R, Scope, SE, Params,
false);
/* Fall through */
}
if (!OrExpr)
return false;
return isAffineParamExpr(V, R, Scope, SE, Params);
}
std::vector<const SCEV *> getParamsInAffineExpr(const Region *R, Loop *Scope,
const SCEV *Expr,
ScalarEvolution &SE,
const Value *BaseAddress) {
if (isa<SCEVCouldNotCompute>(Expr))
return std::vector<const SCEV *>();
InvariantLoadsSetTy ILS;
SCEVValidator Validator(R, Scope, SE, BaseAddress, &ILS);
ValidatorResult Result = Validator.visit(Expr);
assert(Result.isValid() && "Requested parameters for an invalid SCEV!");
return Result.getParameters();
}
std::pair<const SCEVConstant *, const SCEV *>
extractConstantFactor(const SCEV *S, ScalarEvolution &SE) {
auto *LeftOver = SE.getConstant(S->getType(), 1);
auto *ConstPart = cast<SCEVConstant>(SE.getConstant(S->getType(), 1));
if (auto *Constant = dyn_cast<SCEVConstant>(S))
return std::make_pair(Constant, LeftOver);
auto *AddRec = dyn_cast<SCEVAddRecExpr>(S);
if (AddRec) {
auto *StartExpr = AddRec->getStart();
if (StartExpr->isZero()) {
auto StepPair = extractConstantFactor(AddRec->getStepRecurrence(SE), SE);
auto *LeftOverAddRec =
SE.getAddRecExpr(StartExpr, StepPair.second, AddRec->getLoop(),
AddRec->getNoWrapFlags());
return std::make_pair(StepPair.first, LeftOverAddRec);
}
return std::make_pair(ConstPart, S);
}
auto *Mul = dyn_cast<SCEVMulExpr>(S);
if (!Mul)
return std::make_pair(ConstPart, S);
for (auto *Op : Mul->operands())
if (isa<SCEVConstant>(Op))
ConstPart = cast<SCEVConstant>(SE.getMulExpr(ConstPart, Op));
else
LeftOver = SE.getMulExpr(LeftOver, Op);
return std::make_pair(ConstPart, LeftOver);
}
}