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| -rw-r--r-- | compilerplugins/clang/passparamsbyref.cxx | 234 |
1 files changed, 234 insertions, 0 deletions
diff --git a/compilerplugins/clang/passparamsbyref.cxx b/compilerplugins/clang/passparamsbyref.cxx new file mode 100644 index 000000000..9a3562752 --- /dev/null +++ b/compilerplugins/clang/passparamsbyref.cxx @@ -0,0 +1,234 @@ +/* -*- 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/. + */ +#ifndef LO_CLANG_SHARED_PLUGINS + +#include <string> +#include <unordered_set> + +#include "check.hxx" +#include "compat.hxx" +#include "plugin.hxx" + +// Find places where parameters are passed by value +// It's not very efficient, because we generally end up copying it twice - once into the parameter and +// again into the destination. +// They should rather be passed by reference. +// +// Generally recommending lambda capture by-ref rather than by-copy is even more +// problematic than with function parameters, as a lambda instance can easily +// outlive a referenced variable. So once lambdas start to get used in more +// sophisticated ways than passing them into standard algorithms, this plugin's +// advice, at least for explicit captures, will need to be revisited. + +namespace { + +class PassParamsByRef: + public loplugin::FilteringPlugin<PassParamsByRef> +{ +public: + explicit PassParamsByRef(loplugin::InstantiationData const & data): FilteringPlugin(data), mbInsideFunctionDecl(false) {} + + virtual void run() override { TraverseDecl(compiler.getASTContext().getTranslationUnitDecl()); } + + // When warning about function params of primitive type that could be passed + // by value instead of by reference, make sure not to warn if the parameter + // is ever bound to a reference; on the one hand, this needs scaffolding in + // all Traverse*Decl functions (indirectly) derived from FunctionDecl; and + // on the other hand, use a hack of ignoring just the DeclRefExprs nested in + // LValueToRValue ImplicitCastExprs when determining whether a param is + // bound to a reference: + bool PreTraverseFunctionDecl(FunctionDecl *); + bool PostTraverseFunctionDecl(FunctionDecl *, bool); + bool TraverseFunctionDecl(FunctionDecl *); + bool PreTraverseImplicitCastExpr(ImplicitCastExpr *); + bool TraverseImplicitCastExpr(ImplicitCastExpr *); + + bool VisitBinaryOperator(BinaryOperator const *); + bool VisitCXXOperatorCallExpr(const CXXOperatorCallExpr *); + +private: + bool isFat(QualType type); + + bool mbInsideFunctionDecl; + std::unordered_set<ParmVarDecl const *> mParamExclusions; +}; + +bool PassParamsByRef::PreTraverseFunctionDecl(FunctionDecl* functionDecl) +{ + if (ignoreLocation(functionDecl)) + return false; + if (functionDecl->isDeleted() + || functionDecl->isFunctionTemplateSpecialization()) + { + return false; + } + // only consider base declarations, not overridden ones, or we warn on methods that + // are overriding stuff from external libraries + const CXXMethodDecl * methodDecl = dyn_cast<CXXMethodDecl>(functionDecl); + if (methodDecl && methodDecl->size_overridden_methods() > 0) + return false; + + // Only warn on the definition of the function: + if (!functionDecl->doesThisDeclarationHaveABody()) + return false; + + mbInsideFunctionDecl = true; + mParamExclusions.clear(); + return true; +} + +bool PassParamsByRef::PostTraverseFunctionDecl(FunctionDecl* functionDecl, bool) +{ + mbInsideFunctionDecl = false; + + auto cxxConstructorDecl = dyn_cast<CXXConstructorDecl>(functionDecl); + unsigned n = functionDecl->getNumParams(); + for (unsigned i = 0; i != n; ++i) { + const ParmVarDecl * pvDecl = functionDecl->getParamDecl(i); + auto const t = pvDecl->getType(); + if (!isFat(t)) + continue; + if (mParamExclusions.find(pvDecl) != mParamExclusions.end()) + continue; + // Ignore cases where the parameter is std::move'd. + // This is a fairly simple check, might need some more complexity if the parameter is std::move'd + // somewhere else in the constructor. + bool bFoundMove = false; + if (cxxConstructorDecl) { + for (CXXCtorInitializer const * cxxCtorInitializer : cxxConstructorDecl->inits()) { + if (cxxCtorInitializer->isMemberInitializer()) + { + auto cxxConstructExpr = dyn_cast<CXXConstructExpr>(cxxCtorInitializer->getInit()->IgnoreParenImpCasts()); + if (cxxConstructExpr && cxxConstructExpr->getNumArgs() == 1) + { + if (auto callExpr = dyn_cast<CallExpr>(cxxConstructExpr->getArg(0)->IgnoreParenImpCasts())) { + if (loplugin::DeclCheck(callExpr->getCalleeDecl()).Function("move").StdNamespace()) { + bFoundMove = true; + break; + } + } + } + } + } + } + if (bFoundMove) + continue; + report( + DiagnosticsEngine::Warning, + ("passing %0 by value, rather pass by const lvalue reference"), + pvDecl->getLocation()) + << t << pvDecl->getSourceRange(); + auto can = functionDecl->getCanonicalDecl(); + if (can->getLocation() != functionDecl->getLocation()) { + report( + DiagnosticsEngine::Note, "function is declared here:", + can->getLocation()) + << can->getSourceRange(); + } + } + return true; +} + +bool PassParamsByRef::TraverseFunctionDecl(FunctionDecl* functionDecl) +{ + bool ret = true; + if (PreTraverseFunctionDecl(functionDecl)) + { + ret = RecursiveASTVisitor::TraverseFunctionDecl(functionDecl); + PostTraverseFunctionDecl(functionDecl, ret); + } + return ret; +} + +bool PassParamsByRef::PreTraverseImplicitCastExpr(ImplicitCastExpr * expr) +{ + if (ignoreLocation(expr)) + return false; + if (expr->getCastKind() == CK_LValueToRValue + && isa<DeclRefExpr>(expr->getSubExpr()->IgnoreParenImpCasts())) + return false; + return true; +} + +bool PassParamsByRef::TraverseImplicitCastExpr(ImplicitCastExpr * expr) +{ + bool ret = true; + if (PreTraverseImplicitCastExpr(expr)) + { + ret = RecursiveASTVisitor::TraverseImplicitCastExpr(expr); + } + return ret; +} + +bool PassParamsByRef::VisitBinaryOperator(const BinaryOperator * binaryOperator) +{ + if (binaryOperator->getOpcode() != BO_Assign) { + return true; + } + if (!mbInsideFunctionDecl) + return true; + // if we are assigning to a parameter, it can be inconvenient to make the param pass-by-ref + if (auto declRefExpr = dyn_cast<DeclRefExpr>(binaryOperator->getLHS())) + { + if (auto parmVarDecl = dyn_cast<ParmVarDecl>(declRefExpr->getDecl())) + mParamExclusions.emplace(parmVarDecl); + } + return true; +} + +bool PassParamsByRef::VisitCXXOperatorCallExpr(const CXXOperatorCallExpr * cxxOperatorCallExpr ) +{ + if (!mbInsideFunctionDecl) + return true; + // if we are assigning to a parameter, it can be inconvenient to make the param pass-by-ref + auto op = cxxOperatorCallExpr->getOperator(); + if ( op != clang::OverloadedOperatorKind::OO_Equal + && op != clang::OverloadedOperatorKind::OO_SlashEqual + && op != clang::OverloadedOperatorKind::OO_StarEqual + && op != clang::OverloadedOperatorKind::OO_MinusEqual + && op != clang::OverloadedOperatorKind::OO_PlusEqual) + return true; + auto declRefExpr = dyn_cast<DeclRefExpr>(cxxOperatorCallExpr->getArg(0)); + if (!declRefExpr) + return true; + if (auto parmVarDecl = dyn_cast<ParmVarDecl>(declRefExpr->getDecl())) + mParamExclusions.emplace(parmVarDecl); + return true; +} + +bool PassParamsByRef::isFat(QualType type) { + if (!type->isRecordType()) { + return false; + } + loplugin::TypeCheck tc(type); + if ((tc.Class("Reference").Namespace("uno").Namespace("star") + .Namespace("sun").Namespace("com").GlobalNamespace()) + || (tc.Class("Sequence").Namespace("uno").Namespace("star") + .Namespace("sun").Namespace("com").GlobalNamespace()) + || tc.Class("OString").Namespace("rtl").GlobalNamespace() + || tc.Class("OUString").Namespace("rtl").GlobalNamespace() + || tc.Class("Reference").Namespace("rtl").GlobalNamespace()) + { + return true; + } + if (type->isIncompleteType()) { + return false; + } + clang::Type const * t2 = type.getTypePtrOrNull(); + return t2 != nullptr + && compiler.getASTContext().getTypeSizeInChars(t2).getQuantity() > 64; +} + +loplugin::Plugin::Registration< PassParamsByRef > passparamsbyref("passparamsbyref"); + +} // namespace + +#endif // LO_CLANG_SHARED_PLUGINS + +/* vim:set shiftwidth=4 softtabstop=4 expandtab: */ |