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//===-- SimplifyConstraints.cpp ---------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "clang/Analysis/FlowSensitive/SimplifyConstraints.h"
#include "llvm/ADT/EquivalenceClasses.h"
namespace clang {
namespace dataflow {
// Substitutes all occurrences of a given atom in `F` by a given formula and
// returns the resulting formula.
static const Formula &
substitute(const Formula &F,
const llvm::DenseMap<Atom, const Formula *> &Substitutions,
Arena &arena) {
switch (F.kind()) {
case Formula::AtomRef:
if (auto iter = Substitutions.find(F.getAtom());
iter != Substitutions.end())
return *iter->second;
return F;
case Formula::Literal:
return F;
case Formula::Not:
return arena.makeNot(substitute(*F.operands()[0], Substitutions, arena));
case Formula::And:
return arena.makeAnd(substitute(*F.operands()[0], Substitutions, arena),
substitute(*F.operands()[1], Substitutions, arena));
case Formula::Or:
return arena.makeOr(substitute(*F.operands()[0], Substitutions, arena),
substitute(*F.operands()[1], Substitutions, arena));
case Formula::Implies:
return arena.makeImplies(
substitute(*F.operands()[0], Substitutions, arena),
substitute(*F.operands()[1], Substitutions, arena));
case Formula::Equal:
return arena.makeEquals(substitute(*F.operands()[0], Substitutions, arena),
substitute(*F.operands()[1], Substitutions, arena));
}
llvm_unreachable("Unknown formula kind");
}
// Returns the result of replacing atoms in `Atoms` with the leader of their
// equivalence class in `EquivalentAtoms`.
// Atoms that don't have an equivalence class in `EquivalentAtoms` are inserted
// into it as single-member equivalence classes.
static llvm::DenseSet<Atom>
projectToLeaders(const llvm::DenseSet<Atom> &Atoms,
llvm::EquivalenceClasses<Atom> &EquivalentAtoms) {
llvm::DenseSet<Atom> Result;
for (Atom Atom : Atoms)
Result.insert(EquivalentAtoms.getOrInsertLeaderValue(Atom));
return Result;
}
// Returns the atoms in the equivalence class for the leader identified by
// `LeaderIt`.
static llvm::SmallVector<Atom>
atomsInEquivalenceClass(const llvm::EquivalenceClasses<Atom> &EquivalentAtoms,
const Atom &At) {
llvm::SmallVector<Atom> Result;
for (auto MemberIt = EquivalentAtoms.findLeader(At);
MemberIt != EquivalentAtoms.member_end(); ++MemberIt)
Result.push_back(*MemberIt);
return Result;
}
void simplifyConstraints(llvm::SetVector<const Formula *> &Constraints,
Arena &arena, SimplifyConstraintsInfo *Info) {
auto contradiction = [&]() {
Constraints.clear();
Constraints.insert(&arena.makeLiteral(false));
};
llvm::EquivalenceClasses<Atom> EquivalentAtoms;
llvm::DenseSet<Atom> TrueAtoms;
llvm::DenseSet<Atom> FalseAtoms;
while (true) {
for (const auto *Constraint : Constraints) {
switch (Constraint->kind()) {
case Formula::AtomRef:
TrueAtoms.insert(Constraint->getAtom());
break;
case Formula::Not:
if (Constraint->operands()[0]->kind() == Formula::AtomRef)
FalseAtoms.insert(Constraint->operands()[0]->getAtom());
break;
case Formula::Equal: {
ArrayRef<const Formula *> operands = Constraint->operands();
if (operands[0]->kind() == Formula::AtomRef &&
operands[1]->kind() == Formula::AtomRef) {
EquivalentAtoms.unionSets(operands[0]->getAtom(),
operands[1]->getAtom());
}
break;
}
default:
break;
}
}
TrueAtoms = projectToLeaders(TrueAtoms, EquivalentAtoms);
FalseAtoms = projectToLeaders(FalseAtoms, EquivalentAtoms);
llvm::DenseMap<Atom, const Formula *> Substitutions;
for (const auto &E : EquivalentAtoms) {
Atom TheAtom = E->getData();
Atom Leader = EquivalentAtoms.getLeaderValue(TheAtom);
if (TrueAtoms.contains(Leader)) {
if (FalseAtoms.contains(Leader)) {
contradiction();
return;
}
Substitutions.insert({TheAtom, &arena.makeLiteral(true)});
} else if (FalseAtoms.contains(Leader)) {
Substitutions.insert({TheAtom, &arena.makeLiteral(false)});
} else if (TheAtom != Leader) {
Substitutions.insert({TheAtom, &arena.makeAtomRef(Leader)});
}
}
llvm::SetVector<const Formula *> NewConstraints;
for (const auto *Constraint : Constraints) {
const Formula &NewConstraint =
substitute(*Constraint, Substitutions, arena);
if (NewConstraint.isLiteral(true))
continue;
if (NewConstraint.isLiteral(false)) {
contradiction();
return;
}
if (NewConstraint.kind() == Formula::And) {
NewConstraints.insert(NewConstraint.operands()[0]);
NewConstraints.insert(NewConstraint.operands()[1]);
continue;
}
NewConstraints.insert(&NewConstraint);
}
if (NewConstraints == Constraints)
break;
Constraints = std::move(NewConstraints);
}
if (Info) {
for (const auto &E : EquivalentAtoms) {
if (!E->isLeader())
continue;
Atom At = *EquivalentAtoms.findLeader(*E);
if (TrueAtoms.contains(At) || FalseAtoms.contains(At))
continue;
llvm::SmallVector<Atom> Atoms =
atomsInEquivalenceClass(EquivalentAtoms, At);
if (Atoms.size() == 1)
continue;
std::sort(Atoms.begin(), Atoms.end());
Info->EquivalentAtoms.push_back(std::move(Atoms));
}
for (Atom At : TrueAtoms)
Info->TrueAtoms.append(atomsInEquivalenceClass(EquivalentAtoms, At));
std::sort(Info->TrueAtoms.begin(), Info->TrueAtoms.end());
for (Atom At : FalseAtoms)
Info->FalseAtoms.append(atomsInEquivalenceClass(EquivalentAtoms, At));
std::sort(Info->FalseAtoms.begin(), Info->FalseAtoms.end());
}
}
} // namespace dataflow
} // namespace clang
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