Adding upstream version 4:24.2.0.upstream/4%24.2.0

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 961 insertions, 0 deletions

diff --git a/compilerplugins/clang/unusedvarsglobal.cxx b/compilerplugins/clang/unusedvarsglobal.cxx
new file mode 100644
index 0000000000..f74bfedb6c
--- /dev/null
+++ b/compilerplugins/clang/unusedvarsglobal.cxx
@@ -0,0 +1,961 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#if !defined _WIN32 //TODO, #include <sys/file.h>
+
+#include <cassert>
+#include <string>
+#include <iostream>
+#include <fstream>
+#include <unordered_set>
+#include <vector>
+#include <algorithm>
+#include <sys/file.h>
+#include <unistd.h>
+
+#include "config_clang.h"
+
+#include "plugin.hxx"
+#include "compat.hxx"
+#include "check.hxx"
+
+#include "clang/AST/ParentMapContext.h"
+
+/**
+This performs two analyses:
+ (1) look for unused global vars
+ (2) look for global vars that are write-only
+*/
+
+namespace
+{
+struct MyVarInfo
+{
+    const VarDecl* varDecl;
+    std::string fieldName;
+    std::string fieldType;
+    std::string sourceLocation;
+};
+bool operator<(const MyVarInfo& lhs, const MyVarInfo& rhs)
+{
+    return std::tie(lhs.sourceLocation, lhs.fieldName)
+           < std::tie(rhs.sourceLocation, rhs.fieldName);
+}
+
+// try to limit the voluminous output a little
+static std::set<MyVarInfo> readFromSet;
+static std::set<MyVarInfo> writeToSet;
+static std::set<MyVarInfo> definitionSet;
+
+/**
+ * Wrap the different kinds of callable and callee objects in the clang AST so I can define methods that handle everything.
+ */
+class CallerWrapper
+{
+    const CallExpr* m_callExpr;
+    const CXXConstructExpr* m_cxxConstructExpr;
+
+public:
+    CallerWrapper(const CallExpr* callExpr)
+        : m_callExpr(callExpr)
+        , m_cxxConstructExpr(nullptr)
+    {
+    }
+    CallerWrapper(const CXXConstructExpr* cxxConstructExpr)
+        : m_callExpr(nullptr)
+        , m_cxxConstructExpr(cxxConstructExpr)
+    {
+    }
+    unsigned getNumArgs() const
+    {
+        return m_callExpr ? m_callExpr->getNumArgs() : m_cxxConstructExpr->getNumArgs();
+    }
+    const Expr* getArg(unsigned i) const
+    {
+        return m_callExpr ? m_callExpr->getArg(i) : m_cxxConstructExpr->getArg(i);
+    }
+};
+class CalleeWrapper
+{
+    const FunctionDecl* m_calleeFunctionDecl = nullptr;
+    const CXXConstructorDecl* m_cxxConstructorDecl = nullptr;
+    const FunctionProtoType* m_functionPrototype = nullptr;
+
+public:
+    explicit CalleeWrapper(const FunctionDecl* calleeFunctionDecl)
+        : m_calleeFunctionDecl(calleeFunctionDecl)
+    {
+    }
+    explicit CalleeWrapper(const CXXConstructExpr* cxxConstructExpr)
+        : m_cxxConstructorDecl(cxxConstructExpr->getConstructor())
+    {
+    }
+    explicit CalleeWrapper(const FunctionProtoType* functionPrototype)
+        : m_functionPrototype(functionPrototype)
+    {
+    }
+    unsigned getNumParams() const
+    {
+        if (m_calleeFunctionDecl)
+            return m_calleeFunctionDecl->getNumParams();
+        else if (m_cxxConstructorDecl)
+            return m_cxxConstructorDecl->getNumParams();
+        else if (m_functionPrototype->param_type_begin() == m_functionPrototype->param_type_end())
+            // FunctionProtoType will assert if we call getParamTypes() and it has no params
+            return 0;
+        else
+            return m_functionPrototype->getParamTypes().size();
+    }
+    const QualType getParamType(unsigned i) const
+    {
+        if (m_calleeFunctionDecl)
+            return m_calleeFunctionDecl->getParamDecl(i)->getType();
+        else if (m_cxxConstructorDecl)
+            return m_cxxConstructorDecl->getParamDecl(i)->getType();
+        else
+            return m_functionPrototype->getParamTypes()[i];
+    }
+    std::string getNameAsString() const
+    {
+        if (m_calleeFunctionDecl)
+            return m_calleeFunctionDecl->getNameAsString();
+        else if (m_cxxConstructorDecl)
+            return m_cxxConstructorDecl->getNameAsString();
+        else
+            return "";
+    }
+    CXXMethodDecl const* getAsCXXMethodDecl() const
+    {
+        if (m_calleeFunctionDecl)
+            return dyn_cast<CXXMethodDecl>(m_calleeFunctionDecl);
+        return nullptr;
+    }
+};
+
+class UnusedVarsGlobal : public loplugin::FilteringPlugin<UnusedVarsGlobal>
+{
+public:
+    explicit UnusedVarsGlobal(loplugin::InstantiationData const& data)
+        : FilteringPlugin(data)
+    {
+    }
+
+    virtual void run() override;
+
+    bool shouldVisitTemplateInstantiations() const { return true; }
+    bool shouldVisitImplicitCode() const { return true; }
+
+    bool VisitVarDecl(const VarDecl*);
+    bool VisitDeclRefExpr(const DeclRefExpr*);
+    bool TraverseCXXMethodDecl(CXXMethodDecl*);
+    bool TraverseFunctionDecl(FunctionDecl*);
+    bool TraverseIfStmt(IfStmt*);
+
+private:
+    MyVarInfo niceName(const VarDecl*);
+    void checkIfReadFrom(const VarDecl* fieldDecl, const DeclRefExpr* declRefExpr);
+    void checkIfWrittenTo(const VarDecl* fieldDecl, const DeclRefExpr* declRefExpr);
+    bool isSomeKindOfZero(const Expr* arg);
+    bool checkForWriteWhenUsingCollectionType(const CXXMethodDecl* calleeMethodDecl);
+    bool IsPassedByNonConst(const VarDecl* fieldDecl, const Stmt* child, CallerWrapper callExpr,
+                            CalleeWrapper calleeFunctionDecl);
+    compat::optional<CalleeWrapper> getCallee(CallExpr const*);
+
+    // For reasons I do not understand, parentFunctionDecl() is not reliable, so
+    // we store the parent function on the way down the AST.
+    FunctionDecl* insideFunctionDecl = nullptr;
+    std::vector<VarDecl const*> insideConditionalCheckOfVarSet;
+};
+
+void UnusedVarsGlobal::run()
+{
+    handler.enableTreeWideAnalysisMode();
+
+    TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+
+    if (!isUnitTestMode())
+    {
+        // dump all our output in one write call - this is to try and limit IO "crosstalk" between multiple processes
+        // writing to the same logfile
+        std::string output;
+        for (const MyVarInfo& s : readFromSet)
+            output += "read:\t" + s.sourceLocation + "\t" + s.fieldName + "\n";
+        for (const MyVarInfo& s : writeToSet)
+            output += "write:\t" + s.sourceLocation + "\t" + s.fieldName + "\n";
+        for (const MyVarInfo& s : definitionSet)
+            output += "definition:\t" + s.fieldName + "\t" + s.fieldType + "\t" + s.sourceLocation
+                      + "\n";
+        std::ofstream myfile;
+        myfile.open(WORKDIR "/loplugin.unusedvarsglobal.log", std::ios::app | std::ios::out);
+        myfile << output;
+        myfile.close();
+    }
+    else
+    {
+        for (const MyVarInfo& s : readFromSet)
+            report(DiagnosticsEngine::Warning, "read", s.varDecl->getBeginLoc());
+        for (const MyVarInfo& s : writeToSet)
+            report(DiagnosticsEngine::Warning, "write", s.varDecl->getBeginLoc());
+    }
+}
+
+MyVarInfo UnusedVarsGlobal::niceName(const VarDecl* varDecl)
+{
+    MyVarInfo aInfo;
+    aInfo.varDecl = varDecl;
+
+    aInfo.fieldName = varDecl->getNameAsString();
+    // sometimes the name (if it's an anonymous thing) contains the full path of the build folder, which we don't need
+    size_t idx = aInfo.fieldName.find(SRCDIR);
+    if (idx != std::string::npos)
+    {
+        aInfo.fieldName = aInfo.fieldName.replace(idx, strlen(SRCDIR), "");
+    }
+    aInfo.fieldType = varDecl->getType().getAsString();
+
+    SourceLocation expansionLoc
+        = compiler.getSourceManager().getExpansionLoc(varDecl->getLocation());
+    StringRef name = getFilenameOfLocation(expansionLoc);
+    aInfo.sourceLocation
+        = std::string(name.substr(strlen(SRCDIR) + 1)) + ":"
+          + std::to_string(compiler.getSourceManager().getSpellingLineNumber(expansionLoc));
+    loplugin::normalizeDotDotInFilePath(aInfo.sourceLocation);
+
+    return aInfo;
+}
+
+bool UnusedVarsGlobal::VisitVarDecl(const VarDecl* varDecl)
+{
+    varDecl = varDecl->getCanonicalDecl();
+    if (isa<ParmVarDecl>(varDecl))
+        return true;
+    if (!varDecl->hasGlobalStorage())
+        return true;
+    if (!varDecl->getLocation().isValid() || ignoreLocation(varDecl))
+        return true;
+    // ignore stuff that forms part of the stable URE interface
+    if (isInUnoIncludeFile(compiler.getSourceManager().getSpellingLoc(varDecl->getLocation())))
+        return true;
+
+    /**
+     If we have
+        const size_t NB_PRODUCTS = 3;
+        int DefaultProductDir[NB_PRODUCTS] = { 3, 3, 3 };
+     clang will inline the constant "3" and never tell us that we are reading from NB_PRODUCTS,
+     so just ignore integer constants.
+    */
+    auto varType = varDecl->getType();
+    if (varType.isConstQualified() && varType->isIntegerType())
+        return true;
+
+    auto initExpr = varDecl->getAnyInitializer();
+    if (initExpr && !isSomeKindOfZero(initExpr))
+        writeToSet.insert(niceName(varDecl));
+
+    definitionSet.insert(niceName(varDecl));
+    return true;
+}
+
+bool UnusedVarsGlobal::VisitDeclRefExpr(const DeclRefExpr* declRefExpr)
+{
+    const Decl* decl = declRefExpr->getDecl();
+    const VarDecl* varDecl = dyn_cast<VarDecl>(decl);
+    if (!varDecl)
+        return true;
+    if (isa<ParmVarDecl>(varDecl))
+        return true;
+    if (!varDecl->hasGlobalStorage())
+        return true;
+    varDecl = varDecl->getCanonicalDecl();
+    if (!varDecl->getLocation().isValid() || ignoreLocation(varDecl))
+        return true;
+    // ignore stuff that forms part of the stable URE interface
+    if (isInUnoIncludeFile(compiler.getSourceManager().getSpellingLoc(varDecl->getLocation())))
+        return true;
+    checkIfReadFrom(varDecl, declRefExpr);
+    checkIfWrittenTo(varDecl, declRefExpr);
+    return true;
+}
+
+/**
+ Does the expression being used to initialise a field value evaluate to
+ the same as a default value?
+ */
+bool UnusedVarsGlobal::isSomeKindOfZero(const Expr* arg)
+{
+    assert(arg);
+    if (arg->isValueDependent())
+        return false;
+    if (arg->getType().isNull())
+        return false;
+    if (isa<CXXDefaultArgExpr>(arg))
+        arg = dyn_cast<CXXDefaultArgExpr>(arg)->getExpr();
+    arg = arg->IgnoreParenCasts();
+    // ignore this, it seems to trigger an infinite recursion
+    if (isa<UnaryExprOrTypeTraitExpr>(arg))
+        return false;
+    if (auto cxxConstructExpr = dyn_cast<CXXConstructExpr>(arg))
+        return cxxConstructExpr->getConstructor()->isDefaultConstructor();
+    APSInt x1;
+    if (compat::EvaluateAsInt(arg, x1, compiler.getASTContext()))
+        return x1 == 0;
+    if (isa<CXXNullPtrLiteralExpr>(arg))
+        return true;
+    if (isa<MaterializeTemporaryExpr>(arg))
+    {
+        const CXXBindTemporaryExpr* strippedArg
+            = dyn_cast_or_null<CXXBindTemporaryExpr>(arg->IgnoreParenCasts());
+        if (strippedArg)
+        {
+            auto temp = dyn_cast<CXXTemporaryObjectExpr>(strippedArg->getSubExpr());
+            if (temp->getNumArgs() == 0)
+            {
+                if (loplugin::TypeCheck(temp->getType())
+                        .Class("OUString")
+                        .Namespace("rtl")
+                        .GlobalNamespace())
+                    return true;
+                if (loplugin::TypeCheck(temp->getType())
+                        .Class("OString")
+                        .Namespace("rtl")
+                        .GlobalNamespace())
+                    return true;
+                return false;
+            }
+        }
+    }
+
+    // Get the expression contents.
+    // This helps us find params which are always initialised with something like "OUString()".
+    SourceManager& SM = compiler.getSourceManager();
+    SourceLocation startLoc = arg->getBeginLoc();
+    SourceLocation endLoc = arg->getEndLoc();
+    const char* p1 = SM.getCharacterData(startLoc);
+    const char* p2 = SM.getCharacterData(endLoc);
+    if (!p1 || !p2 || (p2 - p1) < 0 || (p2 - p1) > 40)
+        return false;
+    unsigned n = Lexer::MeasureTokenLength(endLoc, SM, compiler.getLangOpts());
+    std::string s(p1, p2 - p1 + n);
+    // strip linefeed and tab characters so they don't interfere with the parsing of the log file
+    std::replace(s.begin(), s.end(), '\r', ' ');
+    std::replace(s.begin(), s.end(), '\n', ' ');
+    std::replace(s.begin(), s.end(), '\t', ' ');
+
+    // now normalize the value. For some params, like OUString, we can pass it as OUString() or "" and they are the same thing
+    if (s == "OUString()")
+        return true;
+    else if (s == "OString()")
+        return true;
+    return false;
+}
+
+static char easytolower(char in)
+{
+    if (in <= 'Z' && in >= 'A')
+        return in - ('Z' - 'z');
+    return in;
+}
+
+bool startswith(const std::string& rStr, const char* pSubStr)
+{
+    return rStr.compare(0, strlen(pSubStr), pSubStr) == 0;
+}
+
+bool UnusedVarsGlobal::TraverseCXXMethodDecl(CXXMethodDecl* cxxMethodDecl)
+{
+    auto copy2 = insideFunctionDecl;
+    insideFunctionDecl = cxxMethodDecl;
+    bool ret = RecursiveASTVisitor::TraverseCXXMethodDecl(cxxMethodDecl);
+    insideFunctionDecl = copy2;
+    return ret;
+}
+
+bool UnusedVarsGlobal::TraverseFunctionDecl(FunctionDecl* functionDecl)
+{
+    auto copy2 = insideFunctionDecl;
+    insideFunctionDecl = functionDecl;
+    bool ret = RecursiveASTVisitor::TraverseFunctionDecl(functionDecl);
+    insideFunctionDecl = copy2;
+    return ret;
+}
+
+bool UnusedVarsGlobal::TraverseIfStmt(IfStmt* ifStmt)
+{
+    VarDecl const* varDecl = nullptr;
+    Expr const* cond = ifStmt->getCond()->IgnoreParenImpCasts();
+
+    if (auto memberCallExpr = dyn_cast<CXXMemberCallExpr>(cond))
+    {
+        if (auto cxxConvert = dyn_cast_or_null<CXXConversionDecl>(memberCallExpr->getMethodDecl()))
+        {
+            if (cxxConvert->getConversionType()->isBooleanType())
+                if (auto declRefExpr = dyn_cast<DeclRefExpr>(
+                        memberCallExpr->getImplicitObjectArgument()->IgnoreParenImpCasts()))
+                    if ((varDecl = dyn_cast<VarDecl>(declRefExpr->getDecl())))
+                        insideConditionalCheckOfVarSet.push_back(varDecl);
+        }
+    }
+    else if (auto declRefExpr = dyn_cast<DeclRefExpr>(cond))
+    {
+        if ((varDecl = dyn_cast<VarDecl>(declRefExpr->getDecl())))
+            insideConditionalCheckOfVarSet.push_back(varDecl);
+    }
+
+    bool ret = RecursiveASTVisitor::TraverseIfStmt(ifStmt);
+    if (varDecl)
+        insideConditionalCheckOfVarSet.pop_back();
+    return ret;
+}
+
+void UnusedVarsGlobal::checkIfReadFrom(const VarDecl* varDecl, const DeclRefExpr* declRefExpr)
+{
+    auto parentsRange = compiler.getASTContext().getParents(*declRefExpr);
+    const Stmt* child = declRefExpr;
+    const Stmt* parent
+        = parentsRange.begin() == parentsRange.end() ? nullptr : parentsRange.begin()->get<Stmt>();
+    // walk up the tree until we find something interesting
+    bool bPotentiallyReadFrom = false;
+    bool bDump = false;
+    auto walkUp = [&]() {
+        child = parent;
+        auto parentsRange = compiler.getASTContext().getParents(*parent);
+        parent = parentsRange.begin() == parentsRange.end() ? nullptr
+                                                            : parentsRange.begin()->get<Stmt>();
+    };
+    do
+    {
+        if (!parent)
+        {
+            // check if we're inside a CXXCtorInitializer or a VarDecl
+            auto parentsRange = compiler.getASTContext().getParents(*child);
+            if (parentsRange.begin() != parentsRange.end())
+            {
+                const Decl* decl = parentsRange.begin()->get<Decl>();
+                if (decl && (isa<CXXConstructorDecl>(decl) || isa<VarDecl>(decl)))
+                    bPotentiallyReadFrom = true;
+            }
+            if (!bPotentiallyReadFrom)
+                return;
+            break;
+        }
+        if (isa<CXXReinterpretCastExpr>(parent))
+        {
+            // once we see one of these, there is not much useful we can know
+            bPotentiallyReadFrom = true;
+            break;
+        }
+        else if (isa<CastExpr>(parent) || isa<MemberExpr>(parent) || isa<ParenExpr>(parent)
+                 || isa<ParenListExpr>(parent) || isa<ArrayInitLoopExpr>(parent)
+                 || isa<ExprWithCleanups>(parent))
+        {
+            walkUp();
+        }
+        else if (auto unaryOperator = dyn_cast<UnaryOperator>(parent))
+        {
+            UnaryOperator::Opcode op = unaryOperator->getOpcode();
+            if (declRefExpr->getType()->isArrayType() && op == UO_Deref)
+            {
+                // ignore, deref'ing an array does not count as a read
+            }
+            else if (op == UO_AddrOf || op == UO_Deref || op == UO_Plus || op == UO_Minus
+                     || op == UO_Not || op == UO_LNot)
+            {
+                bPotentiallyReadFrom = true;
+                break;
+            }
+            /* The following are technically reads, but from a code-sense they're more of a write/modify, so
+                ignore them to find interesting fields that only modified, not usefully read:
+                UO_PreInc / UO_PostInc / UO_PreDec / UO_PostDec
+                But we still walk up in case the result of the expression is used in a read sense.
+            */
+            walkUp();
+        }
+        else if (auto caseStmt = dyn_cast<CaseStmt>(parent))
+        {
+            bPotentiallyReadFrom = caseStmt->getLHS() == child || caseStmt->getRHS() == child;
+            break;
+        }
+        else if (auto ifStmt = dyn_cast<IfStmt>(parent))
+        {
+            bPotentiallyReadFrom = ifStmt->getCond() == child;
+            break;
+        }
+        else if (auto doStmt = dyn_cast<DoStmt>(parent))
+        {
+            bPotentiallyReadFrom = doStmt->getCond() == child;
+            break;
+        }
+        else if (auto arraySubscriptExpr = dyn_cast<ArraySubscriptExpr>(parent))
+        {
+            if (arraySubscriptExpr->getIdx() == child)
+            {
+                bPotentiallyReadFrom = true;
+                break;
+            }
+            walkUp();
+        }
+        else if (auto binaryOp = dyn_cast<BinaryOperator>(parent))
+        {
+            BinaryOperator::Opcode op = binaryOp->getOpcode();
+            const bool assignmentOp = op == BO_Assign || op == BO_MulAssign || op == BO_DivAssign
+                                      || op == BO_RemAssign || op == BO_AddAssign
+                                      || op == BO_SubAssign || op == BO_ShlAssign
+                                      || op == BO_ShrAssign || op == BO_AndAssign
+                                      || op == BO_XorAssign || op == BO_OrAssign;
+            if (binaryOp->getLHS() == child && assignmentOp)
+                break;
+            else
+            {
+                bPotentiallyReadFrom = true;
+                break;
+            }
+        }
+        else if (auto operatorCallExpr = dyn_cast<CXXOperatorCallExpr>(parent))
+        {
+            auto op = operatorCallExpr->getOperator();
+            const bool assignmentOp = op == OO_Equal || op == OO_StarEqual || op == OO_SlashEqual
+                                      || op == OO_PercentEqual || op == OO_PlusEqual
+                                      || op == OO_MinusEqual || op == OO_LessLessEqual
+                                      || op == OO_AmpEqual || op == OO_CaretEqual
+                                      || op == OO_PipeEqual;
+            if (operatorCallExpr->getArg(0) == child && assignmentOp)
+                break;
+            else if (op == OO_GreaterGreaterEqual && operatorCallExpr->getArg(1) == child)
+                break; // this is a write-only call
+            else
+            {
+                bPotentiallyReadFrom = true;
+                break;
+            }
+        }
+        else if (auto cxxMemberCallExpr = dyn_cast<CXXMemberCallExpr>(parent))
+        {
+            bool bWriteOnlyCall = false;
+            const CXXMethodDecl* callee = cxxMemberCallExpr->getMethodDecl();
+            if (callee)
+            {
+                const Expr* tmp = dyn_cast<Expr>(child);
+                if (tmp->isBoundMemberFunction(compiler.getASTContext()))
+                {
+                    tmp = dyn_cast<MemberExpr>(tmp)->getBase();
+                }
+                if (cxxMemberCallExpr->getImplicitObjectArgument() == tmp)
+                {
+                    // FIXME perhaps a better solution here would be some kind of SAL_PARAM_WRITEONLY attribute
+                    // which we could scatter around.
+                    std::string name = callee->getNameAsString();
+                    std::transform(name.begin(), name.end(), name.begin(), easytolower);
+                    if (startswith(name, "emplace") || name == "insert" || name == "erase"
+                        || name == "remove" || name == "remove_if" || name == "sort"
+                        || name == "push_back" || name == "pop_back" || name == "push_front"
+                        || name == "pop_front" || name == "reserve" || name == "resize"
+                        || name == "reset" || name == "clear" || name == "fill")
+                        // write-only modifications to collections
+                        bWriteOnlyCall = true;
+                    else if (name == "dispose" || name == "disposeAndClear" || name == "swap")
+                        // we're abusing the write-only analysis here to look for fields which don't have anything useful
+                        // being done to them, so we're ignoring things like std::vector::clear, std::vector::swap,
+                        // and VclPtr::disposeAndClear
+                        bWriteOnlyCall = true;
+                }
+            }
+            if (!bWriteOnlyCall)
+                bPotentiallyReadFrom = true;
+            break;
+        }
+        else if (auto callExpr = dyn_cast<CallExpr>(parent))
+        {
+            bool bWriteOnlyCall = false;
+            // check for calls to ReadXXX(foo) type methods, where foo is write-only
+            auto callee = getCallee(callExpr);
+            if (callee)
+            {
+                // FIXME perhaps a better solution here would be some kind of SAL_PARAM_WRITEONLY attribute
+                // which we could scatter around.
+                std::string name = callee->getNameAsString();
+                std::transform(name.begin(), name.end(), name.begin(), easytolower);
+                if (startswith(name, "read"))
+                    // this is a write-only call
+                    bWriteOnlyCall = true;
+            }
+            if (!bWriteOnlyCall)
+                bPotentiallyReadFrom = true;
+            break;
+        }
+        else if (isa<ReturnStmt>(parent) || isa<CXXConstructExpr>(parent)
+                 || isa<ConditionalOperator>(parent) || isa<SwitchStmt>(parent)
+                 || isa<DeclStmt>(parent) || isa<WhileStmt>(parent) || isa<CXXNewExpr>(parent)
+                 || isa<ForStmt>(parent) || isa<InitListExpr>(parent)
+                 || isa<CXXDependentScopeMemberExpr>(parent) || isa<UnresolvedMemberExpr>(parent)
+                 || isa<MaterializeTemporaryExpr>(parent))
+        {
+            bPotentiallyReadFrom = true;
+            break;
+        }
+        else if (isa<CXXDeleteExpr>(parent) || isa<UnaryExprOrTypeTraitExpr>(parent)
+                 || isa<CXXUnresolvedConstructExpr>(parent) || isa<CompoundStmt>(parent)
+                 || isa<LabelStmt>(parent) || isa<CXXForRangeStmt>(parent)
+                 || isa<CXXTypeidExpr>(parent) || isa<DefaultStmt>(parent)
+                 || isa<GCCAsmStmt>(parent) || isa<LambdaExpr>(parent) // TODO
+                 || isa<CXXDefaultArgExpr>(parent) || isa<AtomicExpr>(parent)
+                 || isa<VAArgExpr>(parent) || isa<DeclRefExpr>(parent) || isa<ConstantExpr>(parent)
+                 || isa<SubstNonTypeTemplateParmExpr>(parent))
+        {
+            break;
+        }
+        else
+        {
+            bPotentiallyReadFrom = true;
+            bDump = true;
+            break;
+        }
+    } while (true);
+
+    if (bDump)
+    {
+        report(DiagnosticsEngine::Warning, "oh dear, what can the matter be?",
+               declRefExpr->getBeginLoc())
+            << declRefExpr->getSourceRange();
+        report(DiagnosticsEngine::Note, "parent over here", parent->getBeginLoc())
+            << parent->getSourceRange();
+        parent->dump();
+        declRefExpr->dump();
+    }
+
+    if (bPotentiallyReadFrom)
+        readFromSet.insert(niceName(varDecl));
+}
+
+void UnusedVarsGlobal::checkIfWrittenTo(const VarDecl* varDecl, const DeclRefExpr* declRefExpr)
+{
+    // if we're inside a block that looks like
+    //   if (varDecl)
+    //       ...
+    // then writes to this field don't matter, because unless we find another write to this field, this field is dead
+    if (std::find(insideConditionalCheckOfVarSet.begin(), insideConditionalCheckOfVarSet.end(),
+                  varDecl)
+        != insideConditionalCheckOfVarSet.end())
+        return;
+
+    auto parentsRange = compiler.getASTContext().getParents(*declRefExpr);
+    const Stmt* child = declRefExpr;
+    const Stmt* parent
+        = parentsRange.begin() == parentsRange.end() ? nullptr : parentsRange.begin()->get<Stmt>();
+    // walk up the tree until we find something interesting
+    bool bPotentiallyWrittenTo = false;
+    bool bDump = false;
+    auto walkUp = [&]() {
+        child = parent;
+        auto parentsRange = compiler.getASTContext().getParents(*parent);
+        parent = parentsRange.begin() == parentsRange.end() ? nullptr
+                                                            : parentsRange.begin()->get<Stmt>();
+    };
+    do
+    {
+        if (!parent)
+        {
+            // check if we have an expression like
+            //    int& r = m_field;
+            auto parentsRange = compiler.getASTContext().getParents(*child);
+            if (parentsRange.begin() != parentsRange.end())
+            {
+                auto varDecl = dyn_cast_or_null<VarDecl>(parentsRange.begin()->get<Decl>());
+                // The isImplicit() call is to avoid triggering when we see the vardecl which is part of a for-range statement,
+                // which is of type 'T&&' and also an l-value-ref ?
+                if (varDecl && !varDecl->isImplicit()
+                    && loplugin::TypeCheck(varDecl->getType()).LvalueReference().NonConst())
+                {
+                    bPotentiallyWrittenTo = true;
+                }
+            }
+            break;
+        }
+        if (isa<CXXReinterpretCastExpr>(parent))
+        {
+            // once we see one of these, there is not much useful we can know
+            bPotentiallyWrittenTo = true;
+            break;
+        }
+        else if (isa<CastExpr>(parent) || isa<MemberExpr>(parent) || isa<ParenExpr>(parent)
+                 || isa<ParenListExpr>(parent) || isa<ArrayInitLoopExpr>(parent)
+                 || isa<ExprWithCleanups>(parent))
+        {
+            walkUp();
+        }
+        else if (auto unaryOperator = dyn_cast<UnaryOperator>(parent))
+        {
+            UnaryOperator::Opcode op = unaryOperator->getOpcode();
+            if (op == UO_AddrOf || op == UO_PostInc || op == UO_PostDec || op == UO_PreInc
+                || op == UO_PreDec)
+            {
+                bPotentiallyWrittenTo = true;
+            }
+            break;
+        }
+        else if (auto arraySubscriptExpr = dyn_cast<ArraySubscriptExpr>(parent))
+        {
+            if (arraySubscriptExpr->getIdx() == child)
+                break;
+            walkUp();
+        }
+        else if (auto operatorCallExpr = dyn_cast<CXXOperatorCallExpr>(parent))
+        {
+            auto callee = getCallee(operatorCallExpr);
+            if (callee)
+            {
+                // if calling a non-const operator on the field
+                auto calleeMethodDecl = callee->getAsCXXMethodDecl();
+                if (calleeMethodDecl && operatorCallExpr->getArg(0) == child)
+                {
+                    if (!calleeMethodDecl->isConst())
+                        bPotentiallyWrittenTo
+                            = checkForWriteWhenUsingCollectionType(calleeMethodDecl);
+                }
+                else if (IsPassedByNonConst(varDecl, child, operatorCallExpr, *callee))
+                {
+                    bPotentiallyWrittenTo = true;
+                }
+            }
+            else
+                bPotentiallyWrittenTo = true; // conservative, could improve
+            break;
+        }
+        else if (auto cxxMemberCallExpr = dyn_cast<CXXMemberCallExpr>(parent))
+        {
+            const CXXMethodDecl* calleeMethodDecl = cxxMemberCallExpr->getMethodDecl();
+            if (calleeMethodDecl)
+            {
+                // if calling a non-const method on the field
+                const Expr* tmp = dyn_cast<Expr>(child);
+                if (tmp->isBoundMemberFunction(compiler.getASTContext()))
+                {
+                    tmp = dyn_cast<MemberExpr>(tmp)->getBase();
+                }
+                if (cxxMemberCallExpr->getImplicitObjectArgument() == tmp)
+                {
+                    if (!calleeMethodDecl->isConst())
+                        bPotentiallyWrittenTo
+                            = checkForWriteWhenUsingCollectionType(calleeMethodDecl);
+                    break;
+                }
+                else if (IsPassedByNonConst(varDecl, child, cxxMemberCallExpr,
+                                            CalleeWrapper(calleeMethodDecl)))
+                    bPotentiallyWrittenTo = true;
+            }
+            else
+                bPotentiallyWrittenTo = true; // can happen in templates
+            break;
+        }
+        else if (auto cxxConstructExpr = dyn_cast<CXXConstructExpr>(parent))
+        {
+            if (IsPassedByNonConst(varDecl, child, cxxConstructExpr,
+                                   CalleeWrapper(cxxConstructExpr)))
+                bPotentiallyWrittenTo = true;
+            break;
+        }
+        else if (auto callExpr = dyn_cast<CallExpr>(parent))
+        {
+            auto callee = getCallee(callExpr);
+            if (callee)
+            {
+                if (IsPassedByNonConst(varDecl, child, callExpr, *callee))
+                    bPotentiallyWrittenTo = true;
+            }
+            else
+                bPotentiallyWrittenTo = true; // conservative, could improve
+            break;
+        }
+        else if (auto binaryOp = dyn_cast<BinaryOperator>(parent))
+        {
+            BinaryOperator::Opcode op = binaryOp->getOpcode();
+            const bool assignmentOp = op == BO_Assign || op == BO_MulAssign || op == BO_DivAssign
+                                      || op == BO_RemAssign || op == BO_AddAssign
+                                      || op == BO_SubAssign || op == BO_ShlAssign
+                                      || op == BO_ShrAssign || op == BO_AndAssign
+                                      || op == BO_XorAssign || op == BO_OrAssign;
+            if (assignmentOp)
+            {
+                if (binaryOp->getLHS() == child)
+                    bPotentiallyWrittenTo = true;
+                else if (loplugin::TypeCheck(binaryOp->getLHS()->getType())
+                             .LvalueReference()
+                             .NonConst())
+                    // if the LHS is a non-const reference, we could write to the field later on
+                    bPotentiallyWrittenTo = true;
+            }
+            break;
+        }
+        else if (isa<ReturnStmt>(parent))
+        {
+            if (insideFunctionDecl)
+            {
+                auto tc = loplugin::TypeCheck(insideFunctionDecl->getReturnType());
+                if (tc.LvalueReference().NonConst())
+                    bPotentiallyWrittenTo = true;
+            }
+            break;
+        }
+        else if (isa<ConditionalOperator>(parent) || isa<SwitchStmt>(parent)
+                 || isa<DeclStmt>(parent) || isa<WhileStmt>(parent) || isa<CXXNewExpr>(parent)
+                 || isa<ForStmt>(parent) || isa<InitListExpr>(parent)
+                 || isa<CXXDependentScopeMemberExpr>(parent) || isa<UnresolvedMemberExpr>(parent)
+                 || isa<MaterializeTemporaryExpr>(parent) || isa<IfStmt>(parent)
+                 || isa<DoStmt>(parent) || isa<CXXDeleteExpr>(parent)
+                 || isa<UnaryExprOrTypeTraitExpr>(parent) || isa<CXXUnresolvedConstructExpr>(parent)
+                 || isa<CompoundStmt>(parent) || isa<LabelStmt>(parent)
+                 || isa<CXXForRangeStmt>(parent) || isa<CXXTypeidExpr>(parent)
+                 || isa<DefaultStmt>(parent) || isa<GCCAsmStmt>(parent) || isa<ConstantExpr>(parent)
+                 || isa<AtomicExpr>(parent) || isa<CXXDefaultArgExpr>(parent)
+                 || isa<VAArgExpr>(parent) || isa<DeclRefExpr>(parent)
+                 || isa<SubstNonTypeTemplateParmExpr>(parent) || isa<LambdaExpr>(parent)) // TODO
+        {
+            break;
+        }
+        else
+        {
+            bPotentiallyWrittenTo = true;
+            bDump = true;
+            break;
+        }
+    } while (true);
+
+    if (bDump)
+    {
+        report(DiagnosticsEngine::Warning, "oh dear, what can the matter be? writtenTo=%0",
+               declRefExpr->getBeginLoc())
+            << bPotentiallyWrittenTo << declRefExpr->getSourceRange();
+        if (parent)
+        {
+            report(DiagnosticsEngine::Note, "parent over here", parent->getBeginLoc())
+                << parent->getSourceRange();
+            parent->dump();
+        }
+        declRefExpr->dump();
+        varDecl->getType()->dump();
+    }
+
+    if (bPotentiallyWrittenTo)
+        writeToSet.insert(niceName(varDecl));
+}
+
+// return true if this not a collection type, or if it is a collection type, and we might be writing to it
+bool UnusedVarsGlobal::checkForWriteWhenUsingCollectionType(const CXXMethodDecl* calleeMethodDecl)
+{
+    auto const tc = loplugin::TypeCheck(calleeMethodDecl->getParent());
+    bool listLike = false, setLike = false, mapLike = false, cssSequence = false;
+    if (tc.Class("deque").StdNamespace() || tc.Class("list").StdNamespace()
+        || tc.Class("queue").StdNamespace() || tc.Class("vector").StdNamespace())
+    {
+        listLike = true;
+    }
+    else if (tc.Class("set").StdNamespace() || tc.Class("unordered_set").StdNamespace())
+    {
+        setLike = true;
+    }
+    else if (tc.Class("map").StdNamespace() || tc.Class("unordered_map").StdNamespace())
+    {
+        mapLike = true;
+    }
+    else if (tc.Class("Sequence")
+                 .Namespace("uno")
+                 .Namespace("star")
+                 .Namespace("sun")
+                 .Namespace("com")
+                 .GlobalNamespace())
+    {
+        cssSequence = true;
+    }
+    else
+        return true;
+
+    if (calleeMethodDecl->isOverloadedOperator())
+    {
+        auto oo = calleeMethodDecl->getOverloadedOperator();
+        if (oo == OO_Equal)
+            return true;
+        // This is operator[]. We only care about things that add elements to the collection.
+        // if nothing modifies the size of the collection, then nothing useful
+        // is stored in it.
+        if (listLike)
+            return false;
+        return true;
+    }
+
+    auto name = calleeMethodDecl->getName();
+    if (listLike || setLike || mapLike)
+    {
+        if (name == "reserve" || name == "shrink_to_fit" || name == "clear" || name == "erase"
+            || name == "pop_back" || name == "pop_front" || name == "front" || name == "back"
+            || name == "data" || name == "remove" || name == "remove_if" || name == "unique"
+            || name == "sort" || name == "begin" || name == "end" || name == "rbegin"
+            || name == "rend" || name == "at" || name == "find" || name == "equal_range"
+            || name == "lower_bound" || name == "upper_bound")
+            return false;
+    }
+    if (cssSequence)
+    {
+        if (name == "getArray" || name == "begin" || name == "end")
+            return false;
+    }
+
+    return true;
+}
+
+bool UnusedVarsGlobal::IsPassedByNonConst(const VarDecl* varDecl, const Stmt* child,
+                                          CallerWrapper callExpr, CalleeWrapper calleeFunctionDecl)
+{
+    unsigned len = std::min(callExpr.getNumArgs(), calleeFunctionDecl.getNumParams());
+    // if it's an array, passing it by value to a method typically means the
+    // callee takes a pointer and can modify the array
+    if (varDecl->getType()->isConstantArrayType())
+    {
+        for (unsigned i = 0; i < len; ++i)
+            if (callExpr.getArg(i) == child)
+                if (loplugin::TypeCheck(calleeFunctionDecl.getParamType(i)).Pointer().NonConst())
+                    return true;
+    }
+    else
+    {
+        for (unsigned i = 0; i < len; ++i)
+            if (callExpr.getArg(i) == child)
+                if (loplugin::TypeCheck(calleeFunctionDecl.getParamType(i))
+                        .LvalueReference()
+                        .NonConst())
+                    return true;
+    }
+    return false;
+}
+
+compat::optional<CalleeWrapper> UnusedVarsGlobal::getCallee(CallExpr const* callExpr)
+{
+    FunctionDecl const* functionDecl = callExpr->getDirectCallee();
+    if (functionDecl)
+        return CalleeWrapper(functionDecl);
+
+    // Extract the functionprototype from a type
+    clang::Type const* calleeType = callExpr->getCallee()->getType().getTypePtr();
+    if (auto pointerType = calleeType->getUnqualifiedDesugaredType()->getAs<clang::PointerType>())
+    {
+        if (auto prototype = pointerType->getPointeeType()
+                                 ->getUnqualifiedDesugaredType()
+                                 ->getAs<FunctionProtoType>())
+        {
+            return CalleeWrapper(prototype);
+        }
+    }
+
+    return compat::optional<CalleeWrapper>();
+}
+
+loplugin::Plugin::Registration<UnusedVarsGlobal> X("unusedvarsglobal", false);
+}
+
+#endif
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */