AddNullariesToAtomlessAggregates.cpp

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/*
 * Souffle - A Datalog Compiler
 * Copyright (c) 2020, The Souffle Developers. All rights reserved
 * Licensed under the Universal Permissive License v 1.0 as shown at:
 * - https://opensource.org/licenses/UPL
 * - <souffle root>/licenses/SOUFFLE-UPL.txt
 */
 
/************************************************************************
 *
 * @file AddNullariesToAtomlessAggregates.cpp
 *
 ***********************************************************************/
 
#include "ast/transform/AddNullariesToAtomlessAggregates.h"
#include "ast/Aggregator.h"
#include "ast/Atom.h"
#include "ast/Clause.h"
#include "ast/Literal.h"
#include "ast/Program.h"
#include "ast/QualifiedName.h"
#include "ast/Relation.h"
#include "ast/TranslationUnit.h"
#include "ast/utility/Utils.h"
#include "ast/utility/Visitor.h"
#include "souffle/utility/MiscUtil.h"
#include <algorithm>
#include <memory>
#include <utility>
#include <vector>
 
namespace souffle::ast::transform {
 
bool AddNullariesToAtomlessAggregatesTransformer::transform(TranslationUnit& translationUnit) {
    bool changed{false};
    Program& program = translationUnit.getProgram();
    visitDepthFirst(program, [&](const Aggregator& agg) {
        bool seenAtom{false};
        for (const auto& literal : agg.getBodyLiterals()) {
            if (isA<Atom>(literal)) {
                seenAtom = true;
            }
        }
        if (seenAtom) {
            return;
        }
        // We will add in the Tautology atom to the body of this aggregate now
        changed = true;
        // +Tautology()
        auto nullaryAtom = mk<Atom>();
        std::string relName = "+Tautology";
        nullaryAtom->setQualifiedName(relName);
 
        if (getRelation(program, relName) == nullptr) {
            // +Tautology().
            auto fact = mk<Clause>();
            fact->setHead(souffle::clone(nullaryAtom));
            // .decl +Tautology()
            auto tautologyRel = mk<Relation>();
            tautologyRel->setQualifiedName(relName);
            program.addRelation(std::move(tautologyRel));
            program.addClause(std::move(fact));
        }
        VecOwn<Literal> newBody;
        for (const auto& lit : agg.getBodyLiterals()) {
            newBody.push_back(souffle::clone(lit));
        }
        newBody.push_back(souffle::clone(nullaryAtom));
        const_cast<Aggregator&>(agg).setBody(std::move(newBody));
    });
    return changed;
}
}  // namespace souffle::ast::transform