Adding upstream version 4:7.4.7.upstream/4%7.4.7upstream

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

1 files changed, 969 insertions, 0 deletions

diff --git a/compilerplugins/clang/redundantcast.cxx b/compilerplugins/clang/redundantcast.cxx
new file mode 100644
index 000000000..87c4d1445
--- /dev/null
+++ b/compilerplugins/clang/redundantcast.cxx
@@ -0,0 +1,969 @@
+/* -*- 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/.
+ */
+
+// Warn about certain redundant casts:
+//
+// * A reinterpret_cast<T*>(...) whose result is then implicitly cast to a void
+//   pointer
+//
+// * A static_cast<T*>(e) where e is of void pointer type and whose result is
+//   then implicitly cast to a void pointer
+//
+// * Various const_casts that are either not needed (like casting away constness
+//   in a delete expression) or are implicitly cast back afterwards
+//
+// C-style casts are ignored because it makes this plugin simpler, and they
+// should eventually be eliminated via loplugin:cstylecast and/or
+// -Wold-style-cast.  That implies that this plugin is only relevant for C++
+// code.
+
+#include "clang/Sema/Sema.h"
+
+#include "check.hxx"
+#include "compat.hxx"
+#include "plugin.hxx"
+#include <iostream>
+
+namespace {
+
+bool isVoidPointer(QualType type) {
+    return type->isPointerType()
+        && type->getAs<clang::PointerType>()->getPointeeType()->isVoidType();
+}
+
+bool isRedundantConstCast(CXXConstCastExpr const * expr) {
+    auto const sub = compat::getSubExprAsWritten(expr);
+    return
+        (expr->getType().getCanonicalType()
+         == sub->getType().getCanonicalType())
+        && (expr->getValueKind() != VK_XValue
+            || sub->getValueKind() == VK_XValue);
+}
+
+bool canConstCastFromTo(Expr const * from, Expr const * to) {
+    auto const k1 = from->getValueKind();
+    auto const k2 = to->getValueKind();
+    return (k2 == VK_LValue && k1 == VK_LValue)
+        || (k2 == VK_XValue
+            && (k1 != compat::VK_PRValue || from->getType()->isRecordType()));
+}
+
+char const * printExprValueKind(ExprValueKind k) {
+    switch (k) {
+    case compat::VK_PRValue:
+        return "prvalue";
+    case VK_LValue:
+        return "lvalue";
+    case VK_XValue:
+        return "xvalue";
+    };
+    llvm_unreachable("unknown ExprValueKind");
+}
+
+enum class AlgebraicType { None, Integer, FloatingPoint };
+
+AlgebraicType algebraicType(clang::Type const & type) {
+    if (type.isIntegralOrEnumerationType()) {
+        return AlgebraicType::Integer;
+    } else if (type.isRealFloatingType()) {
+        return AlgebraicType::FloatingPoint;
+    } else {
+        return AlgebraicType::None;
+    }
+}
+
+// Do not look through FunctionToPointerDecay, but through e.g. NullToPointer:
+Expr const * stopAtFunctionPointerDecay(ExplicitCastExpr const * expr) {
+    auto const e1 = expr->getSubExpr();
+    if (auto const e2 = dyn_cast<ImplicitCastExpr>(e1)) {
+        if (e2->getCastKind() != CK_FunctionToPointerDecay) {
+            return e2->getSubExpr();
+        }
+    }
+    return e1;
+}
+
+class RedundantCast:
+    public loplugin::FilteringRewritePlugin<RedundantCast>
+{
+public:
+    explicit RedundantCast(loplugin::InstantiationData const & data):
+        FilteringRewritePlugin(data)
+    {}
+
+    virtual void run() override {
+        if (compiler.getLangOpts().CPlusPlus) {
+            TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+        }
+    }
+
+    bool TraverseInitListExpr(InitListExpr * expr, DataRecursionQueue * queue = nullptr) {
+        return WalkUpFromInitListExpr(expr)
+            && TraverseSynOrSemInitListExpr(
+                expr->isSemanticForm() ? expr : expr->getSemanticForm(), queue);
+    }
+
+    bool TraverseReturnStmt(ReturnStmt * stmt) {
+        auto const saved = returnExpr_;
+        returnExpr_ = stmt->getRetValue();
+        auto const ret = FilteringRewritePlugin::TraverseReturnStmt(stmt);
+        returnExpr_ = saved;
+        return ret;
+    }
+
+    bool VisitImplicitCastExpr(ImplicitCastExpr const * expr);
+
+    bool VisitCXXStaticCastExpr(CXXStaticCastExpr const * expr);
+
+    bool VisitCXXReinterpretCastExpr(CXXReinterpretCastExpr const * expr);
+
+    bool VisitCXXConstCastExpr(CXXConstCastExpr const * expr);
+
+    bool VisitCXXFunctionalCastExpr(CXXFunctionalCastExpr const * expr);
+
+    bool VisitCXXDynamicCastExpr(CXXDynamicCastExpr const * expr);
+
+    bool VisitCallExpr(CallExpr const * expr);
+
+    bool VisitCXXDeleteExpr(CXXDeleteExpr const * expr);
+
+    bool VisitCStyleCastExpr(CStyleCastExpr const * expr);
+
+    bool VisitBinaryOperator(BinaryOperator const * expr) {
+        auto const op = expr->getOpcode();
+        if (op == BO_Sub || expr->isRelationalOp() || expr->isEqualityOp()) {
+            return visitBinOp(expr);
+        }
+        if (op == BO_Assign) {
+            if (ignoreLocation(expr)) {
+                return true;
+            }
+            visitAssign(expr->getLHS()->getType(), expr->getRHS());
+            return true;
+        }
+        return true;
+    }
+
+    bool VisitVarDecl(VarDecl const * varDecl);
+
+private:
+    bool visitBinOp(BinaryOperator const * expr);
+    void visitAssign(QualType lhs, Expr const * rhs);
+    bool isOverloadedFunction(FunctionDecl const * decl);
+
+    bool isInIgnoredMacroBody(Expr const * expr) {
+        auto const loc = expr->getBeginLoc();
+        return compiler.getSourceManager().isMacroBodyExpansion(loc)
+            && ignoreLocation(compiler.getSourceManager().getSpellingLoc(loc));
+    }
+
+    Expr const * returnExpr_ = nullptr;
+};
+
+bool RedundantCast::VisitImplicitCastExpr(const ImplicitCastExpr * expr) {
+    if (ignoreLocation(expr)) {
+        return true;
+    }
+    switch (expr->getCastKind()) {
+    case CK_NoOp:
+        if (expr->getType()->isPointerType()
+            || expr->getType()->isObjectType())
+        {
+            auto e = dyn_cast<CXXConstCastExpr>(
+                expr->getSubExpr()->IgnoreParenImpCasts());
+            if (e != nullptr && !isRedundantConstCast(e)) {
+                auto t1 = e->getSubExpr()->getType().getCanonicalType();
+                auto t3 = expr->getType().getCanonicalType();
+                bool ObjCLifetimeConversion;
+                if (t1.getTypePtr() == t3.getTypePtr()
+                    || (compiler.getSema().IsQualificationConversion(
+                            t1, t3, false, ObjCLifetimeConversion)
+                        && (e->getType().getCanonicalType().getTypePtr()
+                            != t3.getTypePtr())))
+                {
+                    report(
+                        DiagnosticsEngine::Warning,
+                        ("redundant const_cast from %0 to %1, result is"
+                         " implicitly cast to %2"),
+                        e->getExprLoc())
+                        << e->getSubExprAsWritten()->getType() << e->getType()
+                        << expr->getType() << expr->getSourceRange();
+                }
+            }
+        }
+        break;
+    case CK_BitCast:
+        if (isVoidPointer(expr->getType())
+            && expr->getSubExpr()->getType()->isPointerType())
+        {
+            Expr const * e = expr->getSubExpr()->IgnoreParenImpCasts();
+            while (isa<CXXConstCastExpr>(e)) {
+                auto cc = dyn_cast<CXXConstCastExpr>(e);
+                if (expr->getType()->getAs<clang::PointerType>()
+                    ->getPointeeType().isAtLeastAsQualifiedAs(
+                        cc->getSubExpr()->getType()
+                        ->getAs<clang::PointerType>()->getPointeeType()))
+                {
+                    report(
+                        DiagnosticsEngine::Warning,
+                        ("redundant const_cast from %0 to %1, result is"
+                         " ultimately implicitly cast to %2"),
+                        cc->getExprLoc())
+                        << cc->getSubExprAsWritten()->getType() << cc->getType()
+                        << expr->getType() << expr->getSourceRange();
+                }
+                e = cc->getSubExpr()->IgnoreParenImpCasts();
+            }
+            if (isa<CXXReinterpretCastExpr>(e)) {
+                report(
+                    DiagnosticsEngine::Warning,
+                    ("redundant reinterpret_cast, result is implicitly cast to"
+                     " void pointer"),
+                    e->getExprLoc())
+                    << e->getSourceRange();
+            } else if (isa<CXXStaticCastExpr>(e)
+                       && isVoidPointer(
+                           dyn_cast<CXXStaticCastExpr>(e)->getSubExpr()
+                           ->IgnoreParenImpCasts()->getType())
+                       && !compiler.getSourceManager().isMacroBodyExpansion(
+                           e->getBeginLoc()))
+            {
+                report(
+                    DiagnosticsEngine::Warning,
+                    ("redundant static_cast from void pointer, result is"
+                     " implicitly cast to void pointer"),
+                    e->getExprLoc())
+                    << e->getSourceRange();
+            }
+        }
+        break;
+    case CK_DerivedToBase:
+    case CK_UncheckedDerivedToBase:
+        if (expr->getType()->isPointerType()) {
+            Expr const * e = expr->getSubExpr()->IgnoreParenImpCasts();
+            while (isa<CXXConstCastExpr>(e)) {
+                auto cc = dyn_cast<CXXConstCastExpr>(e);
+                if (expr->getType()->getAs<clang::PointerType>()
+                    ->getPointeeType().isAtLeastAsQualifiedAs(
+                        cc->getSubExpr()->getType()
+                        ->getAs<clang::PointerType>()->getPointeeType()))
+                {
+                    report(
+                        DiagnosticsEngine::Warning,
+                        ("redundant const_cast from %0 to %1, result is"
+                         " ultimately implicitly cast to %2"),
+                        cc->getExprLoc())
+                        << cc->getSubExprAsWritten()->getType() << cc->getType()
+                        << expr->getType() << expr->getSourceRange();
+                }
+                e = cc->getSubExpr()->IgnoreParenImpCasts();
+            }
+        } else if (expr->getType()->isReferenceType()) {
+            Expr const * e = expr->getSubExpr()->IgnoreParenImpCasts();
+            while (isa<CXXConstCastExpr>(e)) {
+                auto cc = dyn_cast<CXXConstCastExpr>(e);
+                if (expr->getType()->getAs<ReferenceType>()->getPointeeType()
+                    .isAtLeastAsQualifiedAs(
+                        cc->getSubExpr()->getType()
+                        ->getAs<ReferenceType>()->getPointeeType()))
+                {
+                    report(
+                        DiagnosticsEngine::Warning,
+                        ("redundant const_cast from %0 to %1, result is"
+                         " ultimately implicitly cast to %2"),
+                        cc->getExprLoc())
+                        << cc->getSubExprAsWritten()->getType() << cc->getType()
+                        << expr->getType() << expr->getSourceRange();
+                }
+                e = cc->getSubExpr()->IgnoreParenImpCasts();
+            }
+        }
+        break;
+    case CK_FloatingToIntegral:
+    case CK_IntegralToFloating:
+        if (auto e = dyn_cast<ExplicitCastExpr>(expr->getSubExpr()->IgnoreParenImpCasts())) {
+            if ((isa<CXXStaticCastExpr>(e) || isa<CXXFunctionalCastExpr>(e))
+                && (algebraicType(*e->getSubExprAsWritten()->getType())
+                    == algebraicType(*expr->getType())))
+            {
+                report(
+                    DiagnosticsEngine::Warning,
+                    ("suspicious %select{static_cast|functional cast}0 from %1 to %2, result is"
+                     " implicitly cast to %3"),
+                    e->getExprLoc())
+                    << isa<CXXFunctionalCastExpr>(e) << e->getSubExprAsWritten()->getType()
+                    << e->getTypeAsWritten() << expr->getType() << expr->getSourceRange();
+            }
+        }
+        break;
+    default:
+        break;
+    }
+    return true;
+}
+
+bool RedundantCast::VisitCStyleCastExpr(CStyleCastExpr const * expr) {
+    if (ignoreLocation(expr)) {
+        return true;
+    }
+    if (isInUnoIncludeFile(compiler.getSourceManager().getSpellingLoc(expr->getBeginLoc()))) {
+        return true;
+    }
+    auto t1 = compat::getSubExprAsWritten(expr)->getType();
+    auto t2 = expr->getTypeAsWritten();
+    if (auto templateType = dyn_cast<SubstTemplateTypeParmType>(t1)) {
+        t1 = templateType->desugar();
+    }
+    if (t1 != t2) {
+        return true;
+    }
+    if (!t1->isBuiltinType() && !loplugin::TypeCheck(t1).Enum() && !loplugin::TypeCheck(t1).Typedef()) {
+        return true;
+    }
+    if (!loplugin::isOkToRemoveArithmeticCast(compiler.getASTContext(), t1, t2, expr->getSubExpr()))
+    {
+        return true;
+    }
+    // Ignore FD_ISSET expanding to "...(SOCKET)(fd)..." in some Microsoft
+    // winsock2.h (TODO: improve heuristic of determining that the whole
+    // expr is part of a single macro body expansion):
+    auto l1 = expr->getBeginLoc();
+    while (compiler.getSourceManager().isMacroArgExpansion(l1)) {
+        l1 = compiler.getSourceManager().getImmediateMacroCallerLoc(l1);
+    }
+    auto l2 = expr->getExprLoc();
+    while (compiler.getSourceManager().isMacroArgExpansion(l2)) {
+        l2 = compiler.getSourceManager().getImmediateMacroCallerLoc(l2);
+    }
+    auto l3 = expr->getEndLoc();
+    while (compiler.getSourceManager().isMacroArgExpansion(l3)) {
+         l3 = compiler.getSourceManager().getImmediateMacroCallerLoc(l3);
+    }
+    if (compiler.getSourceManager().isMacroBodyExpansion(l1)
+        && compiler.getSourceManager().isMacroBodyExpansion(l2)
+        && compiler.getSourceManager().isMacroBodyExpansion(l3)
+        && ignoreLocation(compiler.getSourceManager().getSpellingLoc(l2)))
+    {
+        return true;
+    }
+    report(
+        DiagnosticsEngine::Warning,
+        "redundant cstyle cast from %0 to %1", expr->getExprLoc())
+        << t1 << t2 << expr->getSourceRange();
+    return true;
+}
+
+bool RedundantCast::VisitVarDecl(VarDecl const * varDecl) {
+    if (ignoreLocation(varDecl)) {
+        return true;
+    }
+    if (!varDecl->getInit())
+        return true;
+    visitAssign(varDecl->getType(), varDecl->getInit());
+    return true;
+}
+
+void RedundantCast::visitAssign(QualType t1, Expr const * rhs)
+{
+    auto staticCastExpr = dyn_cast<CXXStaticCastExpr>(rhs->IgnoreImplicit());
+    if (!staticCastExpr)
+        return;
+
+    auto const t2 = staticCastExpr->getSubExpr()->IgnoreImplicit()->getType();
+
+    // if there is more than one copy of the LHS, this cast is resolving ambiguity
+    bool foundOne = false;
+    if (t1->isRecordType())
+    {
+        foundOne = loplugin::derivedFromCount(t2, t1) == 1;
+    }
+    else
+    {
+        auto pointee1 = t1->getPointeeCXXRecordDecl();
+        auto pointee2 = t2->getPointeeCXXRecordDecl();
+        if (pointee1 && pointee2)
+            foundOne = loplugin::derivedFromCount(pointee2, pointee1) == 1;
+    }
+
+    if (foundOne)
+    {
+        report(
+            DiagnosticsEngine::Warning, "redundant static_cast from %0 to %1",
+            staticCastExpr->getExprLoc())
+            << t2 << t1 << staticCastExpr->getSourceRange();
+    }
+}
+
+bool RedundantCast::VisitCXXStaticCastExpr(CXXStaticCastExpr const * expr) {
+    if (ignoreLocation(expr)) {
+        return true;
+    }
+    auto const t2 = expr->getTypeAsWritten();
+    bool const fnptr = t2->isFunctionPointerType() || t2->isMemberFunctionPointerType();
+    auto const sub = fnptr ? stopAtFunctionPointerDecay(expr) : compat::getSubExprAsWritten(expr);
+    auto const t1 = sub->getType();
+    auto const nonClassObjectType = t2->isObjectType()
+        && !(t2->isRecordType() || t2->isArrayType());
+    if (nonClassObjectType && t2.hasLocalQualifiers()) {
+        report(
+            DiagnosticsEngine::Warning,
+            ("in static_cast from %0 %1 to %2 %3, remove redundant top-level"
+             " %select{const qualifier|volatile qualifier|const volatile"
+             " qualifiers}4"),
+            expr->getExprLoc())
+            << t1 << printExprValueKind(sub->getValueKind())
+            << t2 << printExprValueKind(expr->getValueKind())
+            << ((t2.isLocalConstQualified() ? 1 : 0)
+                + (t2.isLocalVolatileQualified() ? 2 : 0) - 1)
+            << expr->getSourceRange();
+        return true;
+    }
+    if (auto const impl = dyn_cast<ImplicitCastExpr>(expr->getSubExpr())) {
+        if (impl->getCastKind() == CK_ArrayToPointerDecay && impl->getType() == t2)
+            //TODO: instead of exact QualType match, allow some variation?
+        {
+            auto const fn = handler.getMainFileName();
+            if (!(loplugin::isSamePathname(
+                      fn, SRCDIR "/sal/qa/rtl/strings/test_ostring_concat.cxx")
+                  || loplugin::isSamePathname(
+                      fn, SRCDIR "/sal/qa/rtl/strings/test_ostring_stringliterals.cxx")
+                  || loplugin::isSamePathname(
+                      fn, SRCDIR "/sal/qa/rtl/strings/test_oustring_concat.cxx")
+                  || loplugin::isSamePathname(
+                      fn, SRCDIR "/sal/qa/rtl/strings/test_oustring_stringliterals.cxx")
+                  || isInIgnoredMacroBody(expr)))
+            {
+                report(
+                    DiagnosticsEngine::Warning, "redundant static_cast from %0 to %1",
+                    expr->getExprLoc())
+                    << expr->getSubExprAsWritten()->getType() << t2 << expr->getSourceRange();
+            }
+            return true;
+        }
+    }
+    auto const t3 = expr->getType();
+    auto const c1 = t1.getCanonicalType();
+    auto const c3 = t3.getCanonicalType();
+    if (nonClassObjectType || !canConstCastFromTo(sub, expr)
+        ? c1.getTypePtr() != c3.getTypePtr() : c1 != c3)
+    {
+        bool ObjCLifetimeConversion;
+        if (nonClassObjectType
+            || (c1.getTypePtr() != c3.getTypePtr()
+                && !compiler.getSema().IsQualificationConversion(
+                    c1, c3, false, ObjCLifetimeConversion)))
+        {
+            return true;
+        }
+        report(
+            DiagnosticsEngine::Warning,
+            "static_cast from %0 %1 to %2 %3 should be written as const_cast",
+            expr->getExprLoc())
+            << t1 << printExprValueKind(sub->getValueKind())
+            << t2 << printExprValueKind(expr->getValueKind())
+            << expr->getSourceRange();
+        return true;
+    }
+    if (!loplugin::isOkToRemoveArithmeticCast(compiler.getASTContext(), t1, t2, expr->getSubExpr()))
+    {
+        return true;
+    }
+    // Don't warn if the types are 'void *' and at least one involves a typedef
+    // (and if both involve typedefs, they're different) (this covers cases like
+    // 'oslModule', or 'CURL *', or casts between 'LPVOID' and 'HANDLE' in
+    // Windows-only code):
+    if (loplugin::TypeCheck(t1).Pointer().NonConstVolatile().Void()) {
+        if (auto const td1 = t1->getAs<TypedefType>()) {
+            auto const td2 = t2->getAs<TypedefType>();
+            if (td2 == nullptr || td2 != td1) {
+                return true;
+            }
+        } else if (auto const td2 = t2->getAs<TypedefType>()) {
+            auto const td1 = t1->getAs<TypedefType>();
+            if (td1 == nullptr || td1 != td2) {
+                return true;
+            }
+        } else {
+            auto const pt1 = t1->getAs<clang::PointerType>()->getPointeeType();
+            auto const pt2 = t2->getAs<clang::PointerType>()->getPointeeType();
+            if (auto const ptd1 = pt1->getAs<TypedefType>()) {
+                auto const ptd2 = pt2->getAs<TypedefType>();
+                if (ptd2 == nullptr || ptd2 != ptd1) {
+                    return true;
+                }
+            } else if (auto const ptd2 = pt2->getAs<TypedefType>()) {
+                auto const ptd1 = pt1->getAs<TypedefType>();
+                if (ptd1 == nullptr || ptd1 != ptd2) {
+                    return true;
+                }
+            }
+        }
+    }
+    auto const k1 = sub->getValueKind();
+    auto const k3 = expr->getValueKind();
+    if ((k3 == VK_XValue && k1 != VK_XValue)
+        || (k3 == VK_LValue && k1 == VK_XValue))
+    {
+        return true;
+    }
+    // For <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2266r1.html> "P2266R1: Simpler
+    // implicit move" (as implemented with <https://github.com/llvm/llvm-project/commit/
+    // bf20631782183cd19e0bb7219e908c2bbb01a75f> "[clang] Implement P2266 Simpler implicit move"
+    // towards Clang 13), don't warn about a static_cast in a return statement like
+    //
+    //   return static_cast<int &>(x);
+    //
+    // that needs an lvalue but where in a return statement like
+    //
+    //   return x;
+    //
+    // the expression would now be an xvalue:
+    if (k3 == VK_LValue && k1 == VK_LValue && returnExpr_ != nullptr
+        && expr == returnExpr_->IgnoreParens())
+    {
+        return true;
+    }
+    // Don't warn if a static_cast on a pointer to function or member function is used to
+    // disambiguate an overloaded function:
+    if (fnptr) {
+        auto e = sub->IgnoreParenImpCasts();
+        if (auto const e1 = dyn_cast<UnaryOperator>(e)) {
+            if (e1->getOpcode() == UO_AddrOf) {
+                e = e1->getSubExpr()->IgnoreParenImpCasts();
+            }
+        }
+        if (auto const e1 = dyn_cast<DeclRefExpr>(e)) {
+            if (auto const fdecl = dyn_cast<FunctionDecl>(e1->getDecl())) {
+                if (isOverloadedFunction(fdecl)) {
+                    return true;
+                }
+            }
+        }
+    }
+    // Suppress warnings from static_cast<bool> in C++ definition of assert in
+    // <https://sourceware.org/git/?p=glibc.git;a=commit;
+    // h=b5889d25e9bf944a89fdd7bcabf3b6c6f6bb6f7c> "assert: Support types
+    // without operator== (int) [BZ #21972]":
+    if (t1->isBooleanType() && t2->isBooleanType()) {
+        auto loc = expr->getBeginLoc();
+        if (compiler.getSourceManager().isMacroBodyExpansion(loc)
+            && (Lexer::getImmediateMacroName(
+                    loc, compiler.getSourceManager(), compiler.getLangOpts())
+                == "assert"))
+        {
+            return true;
+        }
+    }
+    report(
+        DiagnosticsEngine::Warning,
+        ("static_cast from %0 %1 to %2 %3 is redundant%select{| or should be"
+         " written as an explicit construction of a temporary}4"),
+        expr->getExprLoc())
+        << t1 << printExprValueKind(k1) << t2 << printExprValueKind(k3)
+        << (k3 == compat::VK_PRValue && (k1 != compat::VK_PRValue || t1->isRecordType()))
+        << expr->getSourceRange();
+    return true;
+}
+
+bool RedundantCast::VisitCXXReinterpretCastExpr(
+    CXXReinterpretCastExpr const * expr)
+{
+    if (ignoreLocation(expr)) {
+        return true;
+    }
+    if (expr->getTypeAsWritten() == expr->getSubExprAsWritten()->getType())
+        //TODO: instead of exact QualType match, allow some variation?
+    {
+        report(
+            DiagnosticsEngine::Warning, "redundant reinterpret_cast from %0 to %1",
+                expr->getExprLoc())
+                << expr->getSubExprAsWritten()->getType() << expr->getTypeAsWritten()
+                << expr->getSourceRange();
+        return true;
+    }
+    if (auto const sub = dyn_cast<ImplicitCastExpr>(expr->getSubExpr())) {
+        if (sub->getCastKind() == CK_ArrayToPointerDecay && sub->getType() == expr->getType())
+            //TODO: instead of exact QualType match, allow some variation?
+        {
+            if (loplugin::TypeCheck(sub->getType()).Pointer().Const().Char()) {
+                if (auto const lit = dyn_cast<clang::StringLiteral>(expr->getSubExprAsWritten())) {
+                    if (lit->getKind() == clang::StringLiteral::UTF8) {
+                        // Don't warn about
+                        //
+                        //   redundant_cast<char const *>(u8"...")
+                        //
+                        // in pre-C++2a code:
+                        return true;
+                    }
+                }
+            }
+            report(
+                DiagnosticsEngine::Warning, "redundant reinterpret_cast from %0 to %1",
+                expr->getExprLoc())
+                << expr->getSubExprAsWritten()->getType() << expr->getTypeAsWritten()
+                << expr->getSourceRange();
+            return true;
+        }
+    }
+    if (expr->getSubExpr()->getType()->isVoidPointerType()) {
+        auto t = expr->getType()->getAs<clang::PointerType>();
+        if (t == nullptr || !t->getPointeeType()->isObjectType()) {
+            return true;
+        }
+        if (rewriter != nullptr) {
+            auto loc = expr->getBeginLoc();
+            while (compiler.getSourceManager().isMacroArgExpansion(loc)) {
+                loc = compiler.getSourceManager().getImmediateMacroCallerLoc(
+                    loc);
+            }
+            if (compiler.getSourceManager().isMacroBodyExpansion(loc)) {
+                auto loc2 = expr->getEndLoc();
+                while (compiler.getSourceManager().isMacroArgExpansion(loc2)) {
+                    loc2 = compiler.getSourceManager()
+                        .getImmediateMacroCallerLoc(loc2);
+                }
+                if (compiler.getSourceManager().isMacroBodyExpansion(loc2)) {
+                    //TODO: check loc, loc2 are in same macro body expansion
+                    loc = compiler.getSourceManager().getSpellingLoc(loc);
+                }
+            }
+            auto s = compiler.getSourceManager().getCharacterData(loc);
+            auto n = Lexer::MeasureTokenLength(
+                loc, compiler.getSourceManager(), compiler.getLangOpts());
+            std::string tok(s, n);
+            if (tok == "reinterpret_cast" && replaceText(loc, n, "static_cast"))
+            {
+                return true;
+            }
+        }
+        report(
+            DiagnosticsEngine::Warning,
+            "reinterpret_cast from %0 to %1 can be simplified to static_cast",
+            expr->getExprLoc())
+            << expr->getSubExprAsWritten()->getType() << expr->getType()
+            << expr->getSourceRange();
+    } else if (expr->getType()->isVoidPointerType()) {
+        auto t = expr->getSubExpr()->getType()->getAs<clang::PointerType>();
+        if (t == nullptr || !t->getPointeeType()->isObjectType()) {
+            return true;
+        }
+        report(
+            DiagnosticsEngine::Warning,
+            ("reinterpret_cast from %0 to %1 can be simplified to static_cast"
+             " or an implicit conversion"),
+            expr->getExprLoc())
+            << expr->getSubExprAsWritten()->getType() << expr->getType()
+            << expr->getSourceRange();
+    } else if (expr->getType()->isFundamentalType()) {
+        if (auto const sub = dyn_cast<CXXConstCastExpr>(
+                expr->getSubExpr()->IgnoreParens()))
+        {
+            report(
+                DiagnosticsEngine::Warning,
+                ("redundant const_cast from %0 to %1 within reinterpret_cast to"
+                 " fundamental type %2"),
+                expr->getExprLoc())
+                << sub->getSubExprAsWritten()->getType()
+                << sub->getTypeAsWritten() << expr->getTypeAsWritten()
+                << expr->getSourceRange();
+            return true;
+        }
+    }
+    return true;
+}
+
+bool RedundantCast::VisitCXXConstCastExpr(CXXConstCastExpr const * expr) {
+    if (ignoreLocation(expr)) {
+        return true;
+    }
+    auto const sub = compat::getSubExprAsWritten(expr);
+    if (isRedundantConstCast(expr)) {
+        report(
+            DiagnosticsEngine::Warning,
+            "redundant const_cast from %0 %1 to %2 %3", expr->getExprLoc())
+            << sub->getType() << printExprValueKind(sub->getValueKind())
+            << expr->getTypeAsWritten()
+            << printExprValueKind(expr->getValueKind())
+            << expr->getSourceRange();
+        return true;
+    }
+    if (auto const dce = dyn_cast<CXXStaticCastExpr>(
+            sub->IgnoreParenImpCasts()))
+    {
+        auto const sub2 = compat::getSubExprAsWritten(dce);
+        auto t1 = sub2->getType().getCanonicalType();
+        auto isNullptr = t1->isNullPtrType();
+        auto t2 = dce->getType().getCanonicalType();
+        auto t3 = expr->getType().getCanonicalType();
+        auto redundant = false;
+        for (;;) {
+            if ((t2.isConstQualified()
+                 && (isNullptr || !t1.isConstQualified())
+                 && !t3.isConstQualified())
+                || (t2.isVolatileQualified()
+                    && (isNullptr || !t1.isVolatileQualified())
+                    && !t3.isVolatileQualified()))
+            {
+                redundant = true;
+                break;
+            }
+            if (!isNullptr) {
+                auto const p1 = t1->getAs<clang::PointerType>();
+                if (p1 == nullptr) {
+                    break;
+                }
+                t1 = p1->getPointeeType();
+                isNullptr = t1->isNullPtrType();
+            }
+            auto const p2 = t2->getAs<clang::PointerType>();
+            if (p2 == nullptr) {
+                break;
+            }
+            t2 = p2->getPointeeType();
+            auto const p3 = t3->getAs<clang::PointerType>();
+            if (p3 == nullptr) {
+                break;
+            }
+            t3 = p3->getPointeeType();
+        }
+        if (redundant) {
+            report(
+                DiagnosticsEngine::Warning,
+                ("redundant static_cast/const_cast combination from %0 via %1"
+                 " to %2"),
+                expr->getExprLoc())
+                << sub2->getType() << dce->getTypeAsWritten()
+                << expr->getTypeAsWritten() << expr->getSourceRange();
+        }
+    }
+    return true;
+}
+
+bool RedundantCast::VisitCXXFunctionalCastExpr(CXXFunctionalCastExpr const * expr) {
+    if (ignoreLocation(expr)) {
+        return true;
+    }
+    // Restrict this to "real" casts (compared to uses of braced-init-list, like
+    //
+    //   Foo{bar, baz}
+    //
+    // or
+    //
+    //   std::initializer_list<Foo>{bar, baz}
+    //
+    // ), and only to cases where the sub-expression already is a prvalue of
+    // non-class type (and thus the cast is unlikely to be meant to create a
+    // temporary):
+    auto const t1 = expr->getTypeAsWritten();
+    bool const fnptr = t1->isFunctionPointerType() || t1->isMemberFunctionPointerType();
+    auto const sub = fnptr ? stopAtFunctionPointerDecay(expr) : compat::getSubExprAsWritten(expr);
+    if ((sub->getValueKind() != compat::VK_PRValue && !fnptr) || expr->getType()->isRecordType()
+        || isa<InitListExpr>(sub) || isa<CXXStdInitializerListExpr>(sub))
+    {
+        return true;
+    }
+
+    // See "There might even be good reasons(?) not to warn inside explicit
+    // casts" block in compilerplugins/clang/test/cppunitassertequals.cxx:
+    auto const eloc = expr->getExprLoc();
+    if (compiler.getSourceManager().isMacroArgExpansion(eloc)) {
+        auto const name = Lexer::getImmediateMacroName(
+            eloc, compiler.getSourceManager(), compiler.getLangOpts());
+        if (name == "CPPUNIT_ASSERT" || name == "CPPUNIT_ASSERT_MESSAGE") {
+            return true;
+        }
+    }
+
+    // Don't warn if a functional cast on a pointer to function or member function is used to
+    // disambiguate an overloaded function:
+    if (fnptr) {
+        auto e = sub->IgnoreParenImpCasts();
+        if (auto const e1 = dyn_cast<UnaryOperator>(e)) {
+            if (e1->getOpcode() == UO_AddrOf) {
+                e = e1->getSubExpr()->IgnoreParenImpCasts();
+            }
+        }
+        if (auto const e1 = dyn_cast<DeclRefExpr>(e)) {
+            if (auto const fdecl = dyn_cast<FunctionDecl>(e1->getDecl())) {
+                if (isOverloadedFunction(fdecl)) {
+                    return true;
+                }
+            }
+        }
+    }
+
+    // See the commit message of d0e7d020fa405ab94f19916ec96fbd4611da0031
+    // "socket.c -> socket.cxx" for the reason to have
+    //
+    //   bool(FD_ISSET(...))
+    //
+    // in sal/osl/unx/socket.cxx:
+    //TODO: Better check that sub is exactly an expansion of FD_ISSET:
+    if (sub->getEndLoc().isMacroID()) {
+        for (auto loc = sub->getBeginLoc();
+             loc.isMacroID()
+                 && (compiler.getSourceManager()
+                     .isAtStartOfImmediateMacroExpansion(loc));
+             loc = compiler.getSourceManager().getImmediateMacroCallerLoc(loc))
+        {
+            if (Lexer::getImmediateMacroName(
+                    loc, compiler.getSourceManager(), compiler.getLangOpts())
+                == "FD_ISSET")
+            {
+                return true;
+            }
+        }
+    }
+
+    auto const t2 = sub->getType();
+    if (t1.getCanonicalType() != t2.getCanonicalType())
+        return true;
+    if (!loplugin::isOkToRemoveArithmeticCast(compiler.getASTContext(), t1, t2, expr->getSubExpr()))
+        return true;
+    report(
+        DiagnosticsEngine::Warning,
+        "redundant functional cast from %0 to %1", expr->getExprLoc())
+        << t2 << t1 << expr->getSourceRange();
+    return true;
+}
+
+bool RedundantCast::VisitCXXDynamicCastExpr(CXXDynamicCastExpr const * expr) {
+    if (ignoreLocation(expr)) {
+        return true;
+    }
+    auto const sub = compat::getSubExprAsWritten(expr);
+    auto const t1 = expr->getTypeAsWritten();
+    auto const t2 = sub->getType();
+    QualType qt1 = t1.getCanonicalType();
+    QualType qt2 = t2.getCanonicalType();
+    if (qt1 == qt2)
+    {
+        report(
+            DiagnosticsEngine::Warning,
+            "redundant dynamic cast from %0 to %1", expr->getExprLoc())
+            << t2 << t1 << expr->getSourceRange();
+        return true;
+    }
+    if (qt1->isPointerType() && qt2->isPointerType())
+    {
+        // casting from 'T*' to 'const T*' is redundant, so compare without the qualifiers
+        qt1 = qt1->getPointeeType().getUnqualifiedType();
+        qt2 = qt2->getPointeeType().getUnqualifiedType();
+        if (qt1 == qt2)
+        {
+            report(
+                DiagnosticsEngine::Warning,
+                "redundant dynamic cast from %0 to %1", expr->getExprLoc())
+                << t2 << t1 << expr->getSourceRange();
+            return true;
+        }
+        if (qt1->getAsCXXRecordDecl() && qt2->getAsCXXRecordDecl()->isDerivedFrom(qt1->getAsCXXRecordDecl()))
+        {
+            report(
+                DiagnosticsEngine::Warning,
+                "redundant dynamic upcast from %0 to %1", expr->getExprLoc())
+                << t2 << t1 << expr->getSourceRange();
+            return true;
+        }
+    }
+    return true;
+}
+
+bool RedundantCast::VisitCallExpr(CallExpr const * expr) {
+    if (ignoreLocation(expr)) {
+        return true;
+    }
+    auto f = expr->getDirectCallee();
+    if (f == nullptr || !f->isVariadic()
+        || expr->getNumArgs() <= f->getNumParams())
+    {
+        return true;
+    }
+    for (auto i = f->getNumParams(); i != expr->getNumArgs(); ++i) {
+        auto a = expr->getArg(i);
+        if (a->getType()->isPointerType()) {
+            auto e = dyn_cast<CXXConstCastExpr>(a->IgnoreParenImpCasts());
+            if (e != nullptr) {
+                report(
+                    DiagnosticsEngine::Warning,
+                    "redundant const_cast of variadic function argument",
+                    e->getExprLoc())
+                    << expr->getSourceRange();
+            }
+        }
+    }
+    return true;
+}
+
+bool RedundantCast::VisitCXXDeleteExpr(CXXDeleteExpr const * expr) {
+    if (ignoreLocation(expr)) {
+        return true;
+    }
+    auto e = dyn_cast<CXXConstCastExpr>(
+        expr->getArgument()->IgnoreParenImpCasts());
+    if (e != nullptr) {
+        report(
+            DiagnosticsEngine::Warning,
+            "redundant const_cast in delete expression", e->getExprLoc())
+            << expr->getSourceRange();
+    }
+    return true;
+}
+
+bool RedundantCast::visitBinOp(BinaryOperator const * expr) {
+    if (ignoreLocation(expr)) {
+        return true;
+    }
+    if (expr->getLHS()->getType()->isPointerType()
+        && expr->getRHS()->getType()->isPointerType())
+    {
+        auto e = dyn_cast<CXXConstCastExpr>(
+            expr->getLHS()->IgnoreParenImpCasts());
+        if (e != nullptr) {
+            report(
+                DiagnosticsEngine::Warning,
+                "redundant const_cast on lhs of pointer %select{comparison|subtraction}0 expression",
+                e->getExprLoc())
+                << (expr->getOpcode() == BO_Sub) << expr->getSourceRange();
+        }
+        e = dyn_cast<CXXConstCastExpr>(
+            expr->getRHS()->IgnoreParenImpCasts());
+        if (e != nullptr) {
+            report(
+                DiagnosticsEngine::Warning,
+                "redundant const_cast on rhs of pointer %select{comparison|subtraction}0 expression",
+                e->getExprLoc())
+                << (expr->getOpcode() == BO_Sub) << expr->getSourceRange();
+        }
+    }
+    return true;
+}
+
+bool RedundantCast::isOverloadedFunction(FunctionDecl const * decl) {
+    auto const ctx = decl->getDeclContext();
+    if (!ctx->isLookupContext()) {
+        return false;
+    }
+    auto const canon = decl->getCanonicalDecl();
+    auto const res = ctx->lookup(decl->getDeclName());
+    for (auto d = res.begin(); d != res.end(); ++d) {
+        if (auto const f = dyn_cast<FunctionDecl>(*d)) {
+            if (f->getCanonicalDecl() != canon) {
+                return true;
+            }
+        }
+    }
+    return false;
+}
+
+loplugin::Plugin::Registration<RedundantCast> X("redundantcast", true);
+
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */