1 files changed, 151 insertions, 0 deletions
diff --git a/compilerplugins/clang/expressionalwayszero.cxx b/compilerplugins/clang/expressionalwayszero.cxx
new file mode 100644
index 000000000..f741d30c4
--- /dev/null
+++ b/compilerplugins/clang/expressionalwayszero.cxx
@@ -0,0 +1,151 @@
+/* -*- 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/.
+ */
+
+#include <string>
+#include <set>
+#include <iostream>
+#include <fstream>
+
+#include "plugin.hxx"
+#include "compat.hxx"
+#include "check.hxx"
+
+/**
+    Look for & and operator& expressions where the result is always zero.
+    Generally a mistake when people meant to use | or operator|
+*/
+
+namespace
+{
+class ExpressionAlwaysZero : public loplugin::FilteringPlugin<ExpressionAlwaysZero>
+{
+public:
+    explicit ExpressionAlwaysZero(loplugin::InstantiationData const& data)
+        : FilteringPlugin(data)
+    {
+    }
+
+    virtual void run() override
+    {
+        // don't use getMainFileID, it may return "<stdin>"
+        std::string fn(handler.getMainFileName());
+
+        loplugin::normalizeDotDotInFilePath(fn);
+        // encoding of constant value for binary file format
+        if (loplugin::hasPathnamePrefix(fn, SRCDIR "/package/source/zipapi/ZipFile.cxx"))
+            return;
+        // some auto-generated static data
+        if (loplugin::hasPathnamePrefix(fn, SRCDIR "/sal/textenc/tables.cxx"))
+            return;
+        // nested conditional defines that are not worth cleaning up
+        if (loplugin::hasPathnamePrefix(fn, SRCDIR "/opencl/source/openclwrapper.cxx"))
+            return;
+        // some kind of matrix calculation, the compiler will optimise it out anyway
+        if (loplugin::hasPathnamePrefix(fn, SRCDIR "/vcl/source/gdi/bitmap4.cxx"))
+            return;
+        // code follows a pattern
+        if (loplugin::hasPathnamePrefix(fn, SRCDIR "/svx/source/svdraw/svdhdl.cxx"))
+            return;
+        // looks like some kind of TODO marker
+        if (loplugin::hasPathnamePrefix(fn, SRCDIR "/chart2/source/view/main/PropertyMapper.cxx")
+            || loplugin::hasPathnamePrefix(fn, SRCDIR "/sc/source/core/data/formulacell.cxx"))
+            return;
+        TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+    }
+
+    bool VisitBinaryOperator(BinaryOperator const*);
+    bool VisitCXXOperatorCallExpr(CXXOperatorCallExpr const*);
+    bool TraverseStaticAssertDecl(StaticAssertDecl*);
+
+private:
+    // note, abusing std::unique_ptr as a std::optional lookalike
+    std::unique_ptr<APSInt> getExprValue(const Expr* arg);
+};
+
+bool ExpressionAlwaysZero::VisitBinaryOperator(BinaryOperator const* binaryOperator)
+{
+    if (ignoreLocation(binaryOperator))
+        return true;
+    if (binaryOperator->getBeginLoc().isMacroID())
+        return true;
+
+    auto op = binaryOperator->getOpcode();
+    if (!(op == BO_And || op == BO_AndAssign || op == BO_LAnd))
+        return true;
+
+    auto lhsValue = getExprValue(binaryOperator->getLHS());
+    auto rhsValue = getExprValue(binaryOperator->getRHS());
+    if (lhsValue && lhsValue->getExtValue() == 0)
+        ; // ok
+    else if (rhsValue && rhsValue->getExtValue() == 0)
+        ; // ok
+    else if (lhsValue && rhsValue && (lhsValue->getExtValue() & rhsValue->getExtValue()) == 0)
+        ; // ok
+    else
+        return true;
+    report(DiagnosticsEngine::Warning, "expression always evaluates to zero, lhs=%0 rhs=%1",
+           binaryOperator->getBeginLoc())
+        << (lhsValue ? compat::toString(*lhsValue, 10) : "unknown")
+        << (rhsValue ? compat::toString(*rhsValue, 10) : "unknown")
+        << binaryOperator->getSourceRange();
+    return true;
+}
+
+bool ExpressionAlwaysZero::VisitCXXOperatorCallExpr(CXXOperatorCallExpr const* cxxOperatorCallExpr)
+{
+    if (ignoreLocation(cxxOperatorCallExpr))
+        return true;
+    if (cxxOperatorCallExpr->getBeginLoc().isMacroID())
+        return true;
+
+    auto op = cxxOperatorCallExpr->getOperator();
+    if (!(op == OO_Amp || op == OO_AmpEqual || op == OO_AmpAmp))
+        return true;
+
+    if (cxxOperatorCallExpr->getNumArgs() != 2)
+        return true;
+    auto lhsValue = getExprValue(cxxOperatorCallExpr->getArg(0));
+    auto rhsValue = getExprValue(cxxOperatorCallExpr->getArg(1));
+    if (lhsValue && lhsValue->getExtValue() == 0)
+        ; // ok
+    else if (rhsValue && rhsValue->getExtValue() == 0)
+        ; // ok
+    else if (lhsValue && rhsValue && (lhsValue->getExtValue() & rhsValue->getExtValue()) == 0)
+        ; // ok
+    else
+        return true;
+    report(DiagnosticsEngine::Warning, "expression always evaluates to zero, lhs=%0 rhs=%1",
+           cxxOperatorCallExpr->getBeginLoc())
+        << (lhsValue ? compat::toString(*lhsValue, 10) : "unknown")
+        << (rhsValue ? compat::toString(*rhsValue, 10) : "unknown")
+        << cxxOperatorCallExpr->getSourceRange();
+    return true;
+}
+
+std::unique_ptr<APSInt> ExpressionAlwaysZero::getExprValue(Expr const* expr)
+{
+    expr = expr->IgnoreParenCasts();
+    // ignore this, it seems to trigger an infinite recursion
+    if (isa<UnaryExprOrTypeTraitExpr>(expr))
+    {
+        return std::unique_ptr<APSInt>();
+    }
+    APSInt x1;
+    if (!expr->isValueDependent() && compat::EvaluateAsInt(expr, x1, compiler.getASTContext()))
+        return std::unique_ptr<APSInt>(new APSInt(x1));
+    return std::unique_ptr<APSInt>();
+}
+
+// these will often evaluate to zero harmlessly
+bool ExpressionAlwaysZero::TraverseStaticAssertDecl(StaticAssertDecl*) { return true; }
+
+loplugin::Plugin::Registration<ExpressionAlwaysZero> X("expressionalwayszero", false);
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */