cppcheck/lib/infer.cpp

/*
 * Cppcheck - A tool for static C/C++ code analysis
 * Copyright (C) 2007-2021 Cppcheck team.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "infer.h"

#include "calculate.h"
#include "errortypes.h"
#include "valueptr.h"

#include <cassert>
#include <algorithm>
#include <functional>
#include <iterator>
#include <unordered_set>
#include <utility>

class Token;

template<class Predicate, class Compare>
static const ValueFlow::Value* getCompareValue(const std::list<ValueFlow::Value>& values, Predicate pred, Compare compare)
{
    const ValueFlow::Value* result = nullptr;
    for (const ValueFlow::Value& value : values) {
        if (!pred(value))
            continue;
        if (result)
            result = &std::min(value, *result, [compare](const ValueFlow::Value& x, const ValueFlow::Value& y) {
                return compare(x.intvalue, y.intvalue);
            });
        else
            result = &value;
    }
    return result;
}

struct Interval {
    std::vector<MathLib::bigint> minvalue = {};
    std::vector<MathLib::bigint> maxvalue = {};
    std::vector<const ValueFlow::Value*> minRef = {};
    std::vector<const ValueFlow::Value*> maxRef = {};

    std::string str() const
    {
        std::string result = "[";
        if (minvalue.size() == 1)
            result += std::to_string(minvalue.front());
        else
            result += "*";
        result += ",";
        if (maxvalue.size() == 1)
            result += std::to_string(maxvalue.front());
        else
            result += "*";
        result += "]";
        return result;
    }

    void setMinValue(MathLib::bigint x, const ValueFlow::Value* ref = nullptr)
    {
        minvalue = {x};
        if (ref)
            minRef = {ref};
    }

    void setMaxValue(MathLib::bigint x, const ValueFlow::Value* ref = nullptr)
    {
        maxvalue = {x};
        if (ref)
            maxRef = {ref};
    }

    bool isLessThan(MathLib::bigint x, std::vector<const ValueFlow::Value*>* ref = nullptr) const
    {
        if (!this->maxvalue.empty() && this->maxvalue.front() < x) {
            if (ref)
                *ref = maxRef;
            return true;
        }
        return false;
    }

    bool isGreaterThan(MathLib::bigint x, std::vector<const ValueFlow::Value*>* ref = nullptr) const
    {
        if (!this->minvalue.empty() && this->minvalue.front() > x) {
            if (ref)
                *ref = minRef;
            return true;
        }
        return false;
    }

    bool isScalar() const {
        return minvalue.size() == 1 && minvalue == maxvalue;
    }

    bool empty() const {
        return minvalue.empty() && maxvalue.empty();
    }

    bool isScalarOrEmpty() const {
        return empty() || isScalar();
    }

    MathLib::bigint getScalar() const
    {
        assert(isScalar());
        return minvalue.front();
    }

    std::vector<const ValueFlow::Value*> getScalarRef() const
    {
        assert(isScalar());
        if (minRef != maxRef)
            return merge(minRef, maxRef);
        return minRef;
    }

    static Interval fromInt(MathLib::bigint x, const ValueFlow::Value* ref = nullptr)
    {
        Interval result;
        result.setMinValue(x, ref);
        result.setMaxValue(x, ref);
        return result;
    }

    template<class Predicate>
    static Interval fromValues(const std::list<ValueFlow::Value>& values, Predicate predicate)
    {
        Interval result;
        const ValueFlow::Value* minValue = getCompareValue(values, predicate, std::less<MathLib::bigint>{});
        if (minValue) {
            if (minValue->isImpossible() && minValue->bound == ValueFlow::Value::Bound::Upper)
                result.setMinValue(minValue->intvalue + 1, minValue);
            if (minValue->isPossible() && minValue->bound == ValueFlow::Value::Bound::Lower)
                result.setMinValue(minValue->intvalue, minValue);
            if (minValue->isKnown())
                return Interval::fromInt(minValue->intvalue, minValue);
        }
        const ValueFlow::Value* maxValue = getCompareValue(values, predicate, std::greater<MathLib::bigint>{});
        if (maxValue) {
            if (maxValue->isImpossible() && maxValue->bound == ValueFlow::Value::Bound::Lower)
                result.setMaxValue(maxValue->intvalue - 1, maxValue);
            if (maxValue->isPossible() && maxValue->bound == ValueFlow::Value::Bound::Upper)
                result.setMaxValue(maxValue->intvalue, maxValue);
            assert(!maxValue->isKnown());
        }
        return result;
    }

    static Interval fromValues(const std::list<ValueFlow::Value>& values)
    {
        return Interval::fromValues(values, [](const ValueFlow::Value&) {
            return true;
        });
    }

    template<class F>
    static std::vector<MathLib::bigint> apply(const std::vector<MathLib::bigint>& x,
                                              const std::vector<MathLib::bigint>& y,
                                              F f)
    {
        if (x.empty())
            return {};
        if (y.empty())
            return {};
        return {f(x.front(), y.front())};
    }

    static std::vector<const ValueFlow::Value*> merge(std::vector<const ValueFlow::Value*> x,
                                                      const std::vector<const ValueFlow::Value*>& y)
    {
        x.insert(x.end(), y.begin(), y.end());
        return x;
    }

    friend Interval operator-(const Interval& lhs, const Interval& rhs)
    {
        Interval result;
        result.minvalue = Interval::apply(lhs.minvalue, rhs.maxvalue, std::minus<MathLib::bigint>{});
        result.maxvalue = Interval::apply(lhs.maxvalue, rhs.minvalue, std::minus<MathLib::bigint>{});
        if (!result.minvalue.empty())
            result.minRef = merge(lhs.minRef, rhs.maxRef);
        if (!result.maxvalue.empty())
            result.maxRef = merge(lhs.maxRef, rhs.minRef);
        return result;
    }

    static std::vector<int> equal(const Interval& lhs,
                                  const Interval& rhs,
                                  std::vector<const ValueFlow::Value*>* ref = nullptr)
    {
        if (!lhs.isScalar())
            return {};
        if (!rhs.isScalar())
            return {};
        if (ref)
            *ref = merge(lhs.getScalarRef(), rhs.getScalarRef());
        return {lhs.minvalue == rhs.minvalue};
    }

    static std::vector<int> compare(const Interval& lhs,
                                    const Interval& rhs,
                                    std::vector<const ValueFlow::Value*>* ref = nullptr)
    {
        Interval diff = lhs - rhs;
        if (diff.isGreaterThan(0, ref))
            return {1};
        if (diff.isLessThan(0, ref))
            return {-1};
        std::vector<int> eq = Interval::equal(lhs, rhs, ref);
        if (!eq.empty()) {
            if (eq.front() == 0)
                return {1, -1};
            else
                return {0};
        }
        if (diff.isGreaterThan(-1, ref))
            return {0, 1};
        if (diff.isLessThan(1, ref))
            return {0, -1};
        return {};
    }

    static std::vector<bool> compare(const std::string& op,
                                     const Interval& lhs,
                                     const Interval& rhs,
                                     std::vector<const ValueFlow::Value*>* ref = nullptr)
    {
        std::vector<int> r = compare(lhs, rhs, ref);
        if (r.empty())
            return {};
        bool b = calculate(op, r.front(), 0);
        if (std::all_of(r.begin() + 1, r.end(), [&](int i) {
            return b == calculate(op, i, 0);
        }))
            return {b};
        return {};
    }
};

std::string toString(const Interval& i) {
    return i.str();
}

static void addToErrorPath(ValueFlow::Value& value, const std::vector<const ValueFlow::Value*>& refs)
{
    std::unordered_set<const Token*> locations;
    for (const ValueFlow::Value* ref : refs) {
        if (ref->condition && !value.condition)
            value.condition = ref->condition;
        std::copy_if(ref->errorPath.begin(),
                     ref->errorPath.end(),
                     std::back_inserter(value.errorPath),
                     [&](const ErrorPathItem& e) {
            return locations.insert(e.first).second;
        });
    }
}

static void setValueKind(ValueFlow::Value& value, const std::vector<const ValueFlow::Value*>& refs)
{
    bool isPossible = false;
    bool isInconclusive = false;
    for (const ValueFlow::Value* ref : refs) {
        if (ref->isPossible())
            isPossible = true;
        if (ref->isInconclusive())
            isInconclusive = true;
    }
    if (isInconclusive)
        value.setInconclusive();
    else if (isPossible)
        value.setPossible();
    else
        value.setKnown();
}

static bool inferNotEqual(const std::list<ValueFlow::Value>& values, MathLib::bigint x)
{
    return std::any_of(values.begin(), values.end(), [&](const ValueFlow::Value& value) {
        return value.isImpossible() && value.intvalue == x;
    });
}

std::vector<ValueFlow::Value> infer(const ValuePtr<InferModel>& model,
                                    const std::string& op,
                                    std::list<ValueFlow::Value> lhsValues,
                                    std::list<ValueFlow::Value> rhsValues)
{
    std::vector<ValueFlow::Value> result;
    auto notMatch = [&](const ValueFlow::Value& value) {
        return !model->match(value);
    };
    lhsValues.remove_if(notMatch);
    rhsValues.remove_if(notMatch);
    if (lhsValues.empty() || rhsValues.empty())
        return result;

    Interval lhs = Interval::fromValues(lhsValues);
    Interval rhs = Interval::fromValues(rhsValues);

    if (op == "-") {
        Interval diff = lhs - rhs;
        if (diff.isScalar()) {
            std::vector<const ValueFlow::Value*> refs = diff.getScalarRef();
            ValueFlow::Value value(diff.getScalar());
            addToErrorPath(value, refs);
            setValueKind(value, refs);
            result.push_back(value);
        } else {
            if (!diff.minvalue.empty()) {
                ValueFlow::Value value(diff.minvalue.front() - 1);
                value.setImpossible();
                value.bound = ValueFlow::Value::Bound::Upper;
                addToErrorPath(value, diff.minRef);
                result.push_back(value);
            }
            if (!diff.maxvalue.empty()) {
                ValueFlow::Value value(diff.maxvalue.front() + 1);
                value.setImpossible();
                value.bound = ValueFlow::Value::Bound::Lower;
                addToErrorPath(value, diff.maxRef);
                result.push_back(value);
            }
        }
    } else if ((op == "!=" || op == "==") && lhs.isScalarOrEmpty() && rhs.isScalarOrEmpty()) {
        if (lhs.isScalar() && rhs.isScalar()) {
            std::vector<const ValueFlow::Value*> refs = Interval::merge(lhs.getScalarRef(), rhs.getScalarRef());
            ValueFlow::Value value(calculate(op, lhs.getScalar(), rhs.getScalar()));
            addToErrorPath(value, refs);
            setValueKind(value, refs);
            result.push_back(value);
        } else {
            std::vector<const ValueFlow::Value*> refs;
            if (lhs.isScalar() && inferNotEqual(rhsValues, lhs.getScalar()))
                refs = lhs.getScalarRef();
            else if (rhs.isScalar() && inferNotEqual(lhsValues, rhs.getScalar()))
                refs = rhs.getScalarRef();
            if (!refs.empty()) {
                ValueFlow::Value value(op == "!=");
                addToErrorPath(value, refs);
                setValueKind(value, refs);
                result.push_back(value);
            }
        }
    } else {
        std::vector<const ValueFlow::Value*> refs;
        std::vector<bool> r = Interval::compare(op, lhs, rhs, &refs);
        if (!r.empty()) {
            ValueFlow::Value value(r.front());
            addToErrorPath(value, refs);
            setValueKind(value, refs);
            result.push_back(value);
        }
    }

    return result;
}

std::vector<ValueFlow::Value> infer(const ValuePtr<InferModel>& model,
                                    const std::string& op,
                                    MathLib::bigint lhs,
                                    std::list<ValueFlow::Value> rhsValues)
{
    return infer(model, op, {model->yield(lhs)}, std::move(rhsValues));
}

std::vector<ValueFlow::Value> infer(const ValuePtr<InferModel>& model,
                                    const std::string& op,
                                    std::list<ValueFlow::Value> lhsValues,
                                    MathLib::bigint rhs)
{
    return infer(model, op, std::move(lhsValues), {model->yield(rhs)});
}

std::vector<MathLib::bigint> getMinValue(const ValuePtr<InferModel>& model, const std::list<ValueFlow::Value>& values)
{
    return Interval::fromValues(values, [&](const ValueFlow::Value& v) {
        return model->match(v);
    }).minvalue;
}
std::vector<MathLib::bigint> getMaxValue(const ValuePtr<InferModel>& model, const std::list<ValueFlow::Value>& values)
{
    return Interval::fromValues(values, [&](const ValueFlow::Value& v) {
        return model->match(v);
    }).maxvalue;
}