cppcheck/lib/fwdanalysis.cpp

/*
 * Cppcheck - A tool for static C/C++ code analysis
 * Copyright (C) 2007-2023 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 "fwdanalysis.h"

#include "astutils.h"
#include "config.h"
#include "library.h"
#include "symboldatabase.h"
#include "token.h"
#include "vfvalue.h"

#include <list>
#include <map>
#include <string>
#include <utility>

static bool isUnchanged(const Token *startToken, const Token *endToken, const std::set<nonneg int> &exprVarIds, bool local)
{
    for (const Token *tok = startToken; tok != endToken; tok = tok->next()) {
        if (!local && Token::Match(tok, "%name% (") && !Token::simpleMatch(tok->linkAt(1), ") {"))
            // TODO: this is a quick bailout
            return false;
        if (tok->varId() == 0 || exprVarIds.find(tok->varId()) == exprVarIds.end())
            continue;
        const Token *parent = tok;
        while (parent->astParent() && !parent->astParent()->isAssignmentOp() && parent->astParent()->tokType() != Token::Type::eIncDecOp) {
            if (parent->str() == "," || parent->isUnaryOp("&"))
                // TODO: This is a quick bailout
                return false;
            parent = parent->astParent();
        }
        if (parent->astParent()) {
            if (parent->astParent()->tokType() == Token::Type::eIncDecOp)
                return false;
            if (parent->astParent()->isAssignmentOp() && parent == parent->astParent()->astOperand1())
                return false;
        }
    }
    return true;
}

static bool hasFunctionCall(const Token *tok)
{
    if (!tok)
        return false;
    if (Token::Match(tok, "%name% ("))
        // todo, const/pure function?
        return true;
    return hasFunctionCall(tok->astOperand1()) || hasFunctionCall(tok->astOperand2());
}

static bool hasGccCompoundStatement(const Token *tok)
{
    if (!tok)
        return false;
    if (tok->str() == "{" && Token::simpleMatch(tok->previous(), "( {"))
        return true;
    return hasGccCompoundStatement(tok->astOperand1()) || hasGccCompoundStatement(tok->astOperand2());
}

static bool nonLocal(const Variable* var, bool deref)
{
    return !var || (!var->isLocal() && !var->isArgument()) || (deref && var->isArgument() && var->isPointer()) || var->isStatic() || var->isReference() || var->isExtern();
}

static bool hasVolatileCastOrVar(const Token *expr)
{
    bool ret = false;
    visitAstNodes(expr,
                  [&ret](const Token *tok) {
        if (tok->variable() && tok->variable()->isVolatile())
            ret = true;
        else if (Token::simpleMatch(tok, "( volatile"))
            ret = true;
        return ret ? ChildrenToVisit::none : ChildrenToVisit::op1_and_op2;
    });
    return ret;
}

struct FwdAnalysis::Result FwdAnalysis::checkRecursive(const Token *expr, const Token *startToken, const Token *endToken, const std::set<nonneg int> &exprVarIds, bool local, bool inInnerClass, int depth)
{
    // Parse the given tokens
    if (++depth > 1000)
        return Result(Result::Type::BAILOUT);

    for (const Token* tok = startToken; precedes(tok, endToken); tok = tok->next()) {
        if (Token::simpleMatch(tok, "try {")) {
            // TODO: handle try
            return Result(Result::Type::BAILOUT);
        }

        if (Token::simpleMatch(tok, "break ;")) {
            return Result(Result::Type::BREAK, tok);
        }

        if (Token::simpleMatch(tok, "goto"))
            return Result(Result::Type::BAILOUT);

        if (!inInnerClass && tok->str() == "{" && tok->scope()->isClassOrStruct()) {
            // skip returns from local class definition
            FwdAnalysis::Result result = checkRecursive(expr, tok, tok->link(), exprVarIds, local, true, depth);
            if (result.type != Result::Type::NONE)
                return result;
            tok=tok->link();
        }

        if (tok->str() == "continue")
            // TODO
            return Result(Result::Type::BAILOUT);

        if (const Token *lambdaEndToken = findLambdaEndToken(tok)) {
            tok = lambdaEndToken;
            const Result lambdaResult = checkRecursive(expr, lambdaEndToken->link()->next(), lambdaEndToken, exprVarIds, local, inInnerClass, depth);
            if (lambdaResult.type == Result::Type::READ || lambdaResult.type == Result::Type::BAILOUT)
                return lambdaResult;
        }

        if (Token::Match(tok, "return|throw")) {
            // TODO: Handle these better
            // Is expr variable used in expression?

            const Token* opTok = tok->astOperand1();
            if (!opTok)
                opTok = tok->next();
            std::pair<const Token*, const Token*> startEndTokens = opTok->findExpressionStartEndTokens();
            FwdAnalysis::Result result =
                checkRecursive(expr, startEndTokens.first, startEndTokens.second->next(), exprVarIds, local, true, depth);
            if (result.type != Result::Type::NONE)
                return result;

            // #9167: if the return is inside an inner class, it does not tell us anything
            if (!inInnerClass) {
                if (!local && mWhat == What::Reassign)
                    return Result(Result::Type::BAILOUT);

                return Result(Result::Type::RETURN);
            }
        }

        if (tok->str() == "}") {
            // Known value => possible value
            if (tok->scope() == expr->scope())
                mValueFlowKnown = false;

            if (tok->scope()->isLoopScope()) {
                // check condition
                const Token *conditionStart = nullptr;
                const Token *conditionEnd = nullptr;
                if (Token::simpleMatch(tok->link()->previous(), ") {")) {
                    conditionEnd = tok->link()->previous();
                    conditionStart = conditionEnd->link();
                } else if (Token::simpleMatch(tok->link()->previous(), "do {") && Token::simpleMatch(tok, "} while (")) {
                    conditionStart = tok->tokAt(2);
                    conditionEnd = conditionStart->link();
                }
                if (conditionStart && conditionEnd) {
                    bool used = false;
                    for (const Token *condTok = conditionStart; condTok != conditionEnd; condTok = condTok->next()) {
                        if (exprVarIds.find(condTok->varId()) != exprVarIds.end()) {
                            used = true;
                            break;
                        }
                    }
                    if (used)
                        return Result(Result::Type::BAILOUT);
                }

                // check loop body again..
                const struct FwdAnalysis::Result &result = checkRecursive(expr, tok->link(), tok, exprVarIds, local, inInnerClass, depth);
                if (result.type == Result::Type::BAILOUT || result.type == Result::Type::READ)
                    return result;
            }
        }

        if (Token::simpleMatch(tok, "else {"))
            tok = tok->linkAt(1);

        if (Token::simpleMatch(tok, "asm ("))
            return Result(Result::Type::BAILOUT);

        if (mWhat == What::ValueFlow && (Token::Match(tok, "while|for (") || Token::simpleMatch(tok, "do {"))) {
            const Token *bodyStart = nullptr;
            const Token *conditionStart = nullptr;
            if (Token::simpleMatch(tok, "do {")) {
                bodyStart = tok->next();
                if (Token::simpleMatch(bodyStart->link(), "} while ("))
                    conditionStart = bodyStart->link()->tokAt(2);
            } else {
                conditionStart = tok->next();
                if (Token::simpleMatch(conditionStart->link(), ") {"))
                    bodyStart = conditionStart->link()->next();
            }

            if (!bodyStart || !conditionStart)
                return Result(Result::Type::BAILOUT);

            // Is expr changed in condition?
            if (!isUnchanged(conditionStart, conditionStart->link(), exprVarIds, local))
                return Result(Result::Type::BAILOUT);

            // Is expr changed in loop body?
            if (!isUnchanged(bodyStart, bodyStart->link(), exprVarIds, local))
                return Result(Result::Type::BAILOUT);
        }

        if (mWhat == What::ValueFlow && Token::simpleMatch(tok, "if (") && Token::simpleMatch(tok->linkAt(1), ") {")) {
            const Token *bodyStart = tok->linkAt(1)->next();
            const Token *conditionStart = tok->next();
            const Token *condTok = conditionStart->astOperand2();
            if (condTok->hasKnownIntValue()) {
                const bool cond = condTok->values().front().intvalue;
                if (cond) {
                    FwdAnalysis::Result result = checkRecursive(expr, bodyStart, bodyStart->link(), exprVarIds, local, true, depth);
                    if (result.type != Result::Type::NONE)
                        return result;
                } else if (Token::simpleMatch(bodyStart->link(), "} else {")) {
                    bodyStart = bodyStart->link()->tokAt(2);
                    FwdAnalysis::Result result = checkRecursive(expr, bodyStart, bodyStart->link(), exprVarIds, local, true, depth);
                    if (result.type != Result::Type::NONE)
                        return result;
                }
            }
            tok = bodyStart->link();
            if (isReturnScope(tok, &mLibrary))
                return Result(Result::Type::BAILOUT);
            if (Token::simpleMatch(tok, "} else {"))
                tok = tok->linkAt(2);
            if (!tok)
                return Result(Result::Type::BAILOUT);

            // Is expr changed in condition?
            if (!isUnchanged(conditionStart, conditionStart->link(), exprVarIds, local))
                return Result(Result::Type::BAILOUT);

            // Is expr changed in condition body?
            if (!isUnchanged(bodyStart, bodyStart->link(), exprVarIds, local))
                return Result(Result::Type::BAILOUT);
        }

        if (!local && Token::Match(tok, "%name% (") && !Token::simpleMatch(tok->linkAt(1), ") {")) {
            // TODO: this is a quick bailout
            return Result(Result::Type::BAILOUT);
        }

        if (mWhat == What::Reassign &&
            Token::simpleMatch(tok, ";") &&
            Token::simpleMatch(tok->astParent(), ";") &&
            Token::simpleMatch(tok->astParent()->astParent(), "(") &&
            Token::simpleMatch(tok->astParent()->astParent()->previous(), "for (") &&
            !isUnchanged(tok, tok->astParent()->astParent()->link(), exprVarIds, local))
            // TODO: This is a quick bailout to avoid FP #9420, there are false negatives (TODO_ASSERT_EQUALS)
            return Result(Result::Type::BAILOUT);

        if (expr->isName() && Token::Match(tok, "%name% (") && tok->str().find('<') != std::string::npos && tok->str().find(expr->str()) != std::string::npos)
            return Result(Result::Type::BAILOUT);

        if (exprVarIds.find(tok->varId()) != exprVarIds.end()) {
            const Token *parent = tok;
            bool other = false;
            bool same = tok->astParent() && isSameExpression(mCpp, false, expr, tok, mLibrary, true, false, nullptr);
            while (!same && Token::Match(parent->astParent(), "*|.|::|[|(|%cop%")) {
                parent = parent->astParent();
                if (parent->str() == "(" && !parent->isCast())
                    break;
                if (isSameExpression(mCpp, false, expr, parent, mLibrary, true, false, nullptr)) {
                    same = true;
                    if (mWhat == What::ValueFlow) {
                        KnownAndToken v;
                        v.known = mValueFlowKnown;
                        v.token = parent;
                        mValueFlow.push_back(v);
                    }
                }
                if (Token::Match(parent, ". %var%") && parent->next()->varId() && exprVarIds.find(parent->next()->varId()) == exprVarIds.end() &&
                    isSameExpression(mCpp, false, expr->astOperand1(), parent->astOperand1(), mLibrary, true, false, nullptr)) {
                    other = true;
                    break;
                }
            }
            if (mWhat != What::ValueFlow && same && Token::simpleMatch(parent->astParent(), "[") && parent == parent->astParent()->astOperand2()) {
                return Result(Result::Type::READ);
            }
            if (other)
                continue;
            if (Token::simpleMatch(parent->astParent(), "=") && parent == parent->astParent()->astOperand1()) {
                if (!local && hasFunctionCall(parent->astParent()->astOperand2())) {
                    // TODO: this is a quick bailout
                    return Result(Result::Type::BAILOUT);
                }
                if (hasOperand(parent->astParent()->astOperand2(), expr)) {
                    if (mWhat == What::Reassign)
                        return Result(Result::Type::READ);
                    continue;
                }
                const auto startEnd = parent->astParent()->astOperand2()->findExpressionStartEndTokens();
                for (const Token* tok2 = startEnd.first; tok2 != startEnd.second; tok2 = tok2->next()) {
                    if (tok2->tokType() == Token::eLambda)
                        return Result(Result::Type::BAILOUT);
                    // TODO: analyze usage in lambda
                }
                // ({ .. })
                if (hasGccCompoundStatement(parent->astParent()->astOperand2()))
                    return Result(Result::Type::BAILOUT);
                const bool reassign = isSameExpression(mCpp, false, expr, parent, mLibrary, false, false, nullptr);
                if (reassign)
                    return Result(Result::Type::WRITE, parent->astParent());
                return Result(Result::Type::READ);
            }
            if (mWhat == What::Reassign && parent->valueType() && parent->valueType()->pointer && Token::Match(parent->astParent(), "%assign%") && parent == parent->astParent()->astOperand1())
                return Result(Result::Type::READ);

            if (Token::Match(parent->astParent(), "%assign%") && !parent->astParent()->astParent() && parent == parent->astParent()->astOperand1()) {
                if (mWhat == What::Reassign)
                    return Result(Result::Type::BAILOUT, parent->astParent());
                if (mWhat == What::UnusedValue && (!parent->valueType() || parent->valueType()->reference != Reference::None))
                    return Result(Result::Type::BAILOUT, parent->astParent());
                continue;
            }
            if (mWhat == What::UnusedValue && parent->isUnaryOp("&") && Token::Match(parent->astParent(), "[,(]")) {
                // Pass variable to function the writes it
                const Token *ftok = parent->astParent();
                while (Token::simpleMatch(ftok, ","))
                    ftok = ftok->astParent();
                if (ftok && Token::Match(ftok->previous(), "%name% (")) {
                    const std::vector<const Token *> args = getArguments(ftok);
                    int argnr = 0;
                    while (argnr < args.size() && args[argnr] != parent)
                        argnr++;
                    if (argnr < args.size()) {
                        const Library::Function* functionInfo = mLibrary.getFunction(ftok->astOperand1());
                        if (functionInfo) {
                            const auto it = functionInfo->argumentChecks.find(argnr + 1);
                            if (it != functionInfo->argumentChecks.end() && it->second.direction == Library::ArgumentChecks::Direction::DIR_OUT)
                                continue;
                        }
                    }
                }
                return Result(Result::Type::BAILOUT, parent->astParent());
            }
            // TODO: this is a quick bailout
            return Result(Result::Type::BAILOUT, parent->astParent());
        }

        if (Token::Match(tok, ")|do {")) {
            if (tok->str() == ")" && Token::simpleMatch(tok->link()->previous(), "switch ("))
                // TODO: parse switch
                return Result(Result::Type::BAILOUT);
            const Result &result1 = checkRecursive(expr, tok->tokAt(2), tok->linkAt(1), exprVarIds, local, inInnerClass, depth);
            if (result1.type == Result::Type::READ || result1.type == Result::Type::BAILOUT)
                return result1;
            if (mWhat == What::UnusedValue && result1.type == Result::Type::WRITE && expr->variable() && expr->variable()->isReference())
                return result1;
            if (mWhat == What::ValueFlow && result1.type == Result::Type::WRITE)
                mValueFlowKnown = false;
            if (mWhat == What::Reassign && result1.type == Result::Type::BREAK) {
                const Token *scopeEndToken = findNextTokenFromBreak(result1.token);
                if (scopeEndToken) {
                    const Result &result2 = checkRecursive(expr, scopeEndToken->next(), endToken, exprVarIds, local, inInnerClass, depth);
                    if (result2.type == Result::Type::BAILOUT)
                        return result2;
                }
            }
            if (Token::simpleMatch(tok->linkAt(1), "} else {")) {
                const Token *elseStart = tok->linkAt(1)->tokAt(2);
                const Result &result2 = checkRecursive(expr, elseStart, elseStart->link(), exprVarIds, local, inInnerClass, depth);
                if (mWhat == What::ValueFlow && result2.type == Result::Type::WRITE)
                    mValueFlowKnown = false;
                if (result2.type == Result::Type::READ || result2.type == Result::Type::BAILOUT)
                    return result2;
                if (result1.type == Result::Type::WRITE && result2.type == Result::Type::WRITE)
                    return result1;
                tok = elseStart->link();
            } else {
                tok = tok->linkAt(1);
            }
        }
    }

    return Result(Result::Type::NONE);
}

bool FwdAnalysis::isGlobalData(const Token *expr) const
{
    return ::isGlobalData(expr, mCpp);
}

std::set<nonneg int> FwdAnalysis::getExprVarIds(const Token* expr, bool* localOut, bool* unknownVarIdOut) const
{
    // all variable ids in expr.
    std::set<nonneg int> exprVarIds;
    bool local = true;
    bool unknownVarId = false;
    visitAstNodes(expr,
                  [&](const Token *tok) {
        if (tok->str() == "[" && mWhat == What::UnusedValue)
            return ChildrenToVisit::op1;
        if (tok->varId() == 0 && tok->isName() && tok->previous()->str() != ".") {
            // unknown variable
            unknownVarId = true;
            return ChildrenToVisit::none;
        }
        if (tok->varId() > 0) {
            exprVarIds.insert(tok->varId());
            if (!Token::simpleMatch(tok->previous(), ".")) {
                const Variable *var = tok->variable();
                if (var && var->isReference() && var->isLocal() && Token::Match(var->nameToken(), "%var% [=(]") && !isGlobalData(var->nameToken()->next()->astOperand2()))
                    return ChildrenToVisit::none;
                const bool deref = tok->astParent() && (tok->astParent()->isUnaryOp("*") || (tok->astParent()->str() == "[" && tok == tok->astParent()->astOperand1()));
                local &= !nonLocal(tok->variable(), deref);
            }
        }
        return ChildrenToVisit::op1_and_op2;
    });
    if (localOut)
        *localOut = local;
    if (unknownVarIdOut)
        *unknownVarIdOut = unknownVarId;
    return exprVarIds;
}

FwdAnalysis::Result FwdAnalysis::check(const Token* expr, const Token* startToken, const Token* endToken)
{
    // all variable ids in expr.
    bool local = true;
    bool unknownVarId = false;
    std::set<nonneg int> exprVarIds = getExprVarIds(expr, &local, &unknownVarId);

    if (unknownVarId)
        return Result(FwdAnalysis::Result::Type::BAILOUT);

    if (mWhat == What::Reassign && isGlobalData(expr))
        local = false;

    // In unused values checking we do not want to check assignments to
    // global data.
    if (mWhat == What::UnusedValue && isGlobalData(expr))
        return Result(FwdAnalysis::Result::Type::BAILOUT);

    Result result = checkRecursive(expr, startToken, endToken, exprVarIds, local, false);

    // Break => continue checking in outer scope
    while (mWhat!=What::ValueFlow && result.type == FwdAnalysis::Result::Type::BREAK) {
        const Token *scopeEndToken = findNextTokenFromBreak(result.token);
        if (!scopeEndToken)
            break;
        result = checkRecursive(expr, scopeEndToken->next(), endToken, exprVarIds, local, false);
    }

    return result;
}

bool FwdAnalysis::hasOperand(const Token *tok, const Token *lhs) const
{
    if (!tok)
        return false;
    if (isSameExpression(mCpp, false, tok, lhs, mLibrary, false, false, nullptr))
        return true;
    return hasOperand(tok->astOperand1(), lhs) || hasOperand(tok->astOperand2(), lhs);
}

const Token *FwdAnalysis::reassign(const Token *expr, const Token *startToken, const Token *endToken)
{
    if (hasVolatileCastOrVar(expr))
        return nullptr;
    mWhat = What::Reassign;
    Result result = check(expr, startToken, endToken);
    return result.type == FwdAnalysis::Result::Type::WRITE ? result.token : nullptr;
}

bool FwdAnalysis::unusedValue(const Token *expr, const Token *startToken, const Token *endToken)
{
    if (isEscapedAlias(expr))
        return false;
    if (hasVolatileCastOrVar(expr))
        return false;
    if (Token::simpleMatch(expr, "[") && astIsContainerView(expr->astOperand1()))
        return false;
    mWhat = What::UnusedValue;
    Result result = check(expr, startToken, endToken);
    return (result.type == FwdAnalysis::Result::Type::NONE || result.type == FwdAnalysis::Result::Type::RETURN) && !possiblyAliased(expr, startToken);
}

bool FwdAnalysis::possiblyAliased(const Token *expr, const Token *startToken) const
{
    if (expr->isUnaryOp("*") && !expr->astOperand1()->isUnaryOp("&"))
        return true;

    const bool macro = false;
    const bool pure = false;
    const bool followVar = false;
    for (const Token *tok = startToken; tok; tok = tok->previous()) {

        if (Token::Match(tok, "%name% (") && !Token::Match(tok, "if|while|for")) {
            // Is argument passed by reference?
            const std::vector<const Token*> args = getArguments(tok);
            for (int argnr = 0; argnr < args.size(); ++argnr) {
                if (!Token::Match(args[argnr], "%name%|.|::"))
                    continue;
                if (tok->function() && tok->function()->getArgumentVar(argnr) && !tok->function()->getArgumentVar(argnr)->isReference() && !tok->function()->isConst())
                    continue;
                for (const Token *subexpr = expr; subexpr; subexpr = subexpr->astOperand1()) {
                    if (isSameExpression(mCpp, macro, subexpr, args[argnr], mLibrary, pure, followVar)) {
                        const Scope* scope = expr->scope(); // if there is no other variable, assume no aliasing
                        if (scope->varlist.size() > 1)
                            return true;
                    }
                }
            }
            continue;
        }

        const Token *addrOf = nullptr;
        if (Token::Match(tok, "& %name% ="))
            addrOf = tok->tokAt(2)->astOperand2();
        else if (tok->isUnaryOp("&"))
            addrOf = tok->astOperand1();
        else if (Token::simpleMatch(tok, "std :: ref ("))
            addrOf = tok->tokAt(3)->astOperand2();
        else if (tok->valueType() && tok->valueType()->pointer &&
                 (Token::Match(tok, "%var% = %var% ;") || Token::Match(tok, "%var% {|( %var% }|)")) &&
                 Token::Match(expr->previous(), "%varid% [", tok->tokAt(2)->varId()))
            addrOf = tok->tokAt(2);
        else
            continue;

        for (const Token *subexpr = expr; subexpr; subexpr = subexpr->astOperand1()) {
            if (subexpr != addrOf && isSameExpression(mCpp, macro, subexpr, addrOf, mLibrary, pure, followVar))
                return true;
        }
    }
    return false;
}

bool FwdAnalysis::isEscapedAlias(const Token* expr)
{
    for (const Token *subexpr = expr; subexpr; subexpr = subexpr->astOperand1()) {
        for (const ValueFlow::Value &val : subexpr->values()) {
            if (!val.isLocalLifetimeValue())
                continue;
            const Variable* var = val.tokvalue->variable();
            if (!var)
                continue;
            if (!var->isLocal())
                return true;
            if (var->isArgument())
                return true;

        }
    }
    return false;
}