671ad58061
Extend the check to not only look at the variable the unnecessarily copied variable is initialized from, but also ensure that any variable the old variable references is not modified. Extend DeclRefExprUtils to also count references and pointers to const assigned from the DeclRef we check for const usages. Reviewed-by: aaron.ballman Differential Revision: https://reviews.llvm.org/D91893
244 lines
10 KiB
C++
244 lines
10 KiB
C++
//===--- UnnecessaryCopyInitialization.cpp - clang-tidy--------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "UnnecessaryCopyInitialization.h"
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#include "../utils/DeclRefExprUtils.h"
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#include "../utils/FixItHintUtils.h"
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#include "../utils/Matchers.h"
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#include "../utils/OptionsUtils.h"
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#include "clang/Basic/Diagnostic.h"
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namespace clang {
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namespace tidy {
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namespace performance {
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namespace {
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using namespace ::clang::ast_matchers;
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using llvm::StringRef;
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using utils::decl_ref_expr::isOnlyUsedAsConst;
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static constexpr StringRef ObjectArgId = "objectArg";
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static constexpr StringRef InitFunctionCallId = "initFunctionCall";
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static constexpr StringRef OldVarDeclId = "oldVarDecl";
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void recordFixes(const VarDecl &Var, ASTContext &Context,
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DiagnosticBuilder &Diagnostic) {
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Diagnostic << utils::fixit::changeVarDeclToReference(Var, Context);
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if (!Var.getType().isLocalConstQualified()) {
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if (llvm::Optional<FixItHint> Fix = utils::fixit::addQualifierToVarDecl(
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Var, Context, DeclSpec::TQ::TQ_const))
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Diagnostic << *Fix;
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}
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}
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AST_MATCHER_FUNCTION(StatementMatcher, isConstRefReturningMethodCall) {
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// Match method call expressions where the `this` argument is only used as
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// const, this will be checked in `check()` part. This returned const
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// reference is highly likely to outlive the local const reference of the
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// variable being declared. The assumption is that the const reference being
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// returned either points to a global static variable or to a member of the
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// called object.
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return cxxMemberCallExpr(
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callee(cxxMethodDecl(returns(matchers::isReferenceToConst()))),
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on(declRefExpr(to(varDecl().bind(ObjectArgId)))));
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}
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AST_MATCHER_FUNCTION(StatementMatcher, isConstRefReturningFunctionCall) {
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// Only allow initialization of a const reference from a free function if it
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// has no arguments. Otherwise it could return an alias to one of its
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// arguments and the arguments need to be checked for const use as well.
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return callExpr(callee(functionDecl(returns(matchers::isReferenceToConst()))),
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argumentCountIs(0), unless(callee(cxxMethodDecl())))
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.bind(InitFunctionCallId);
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}
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AST_MATCHER_FUNCTION(StatementMatcher, isInitializedFromReferenceToConst) {
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auto OldVarDeclRef =
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declRefExpr(to(varDecl(hasLocalStorage()).bind(OldVarDeclId)));
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return declStmt(has(varDecl(hasInitializer(
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anyOf(isConstRefReturningFunctionCall(), isConstRefReturningMethodCall(),
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ignoringImpCasts(OldVarDeclRef),
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ignoringImpCasts(unaryOperator(
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hasOperatorName("&"), hasUnaryOperand(OldVarDeclRef))))))));
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}
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// This checks that the variable itself is only used as const, and also makes
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// sure that it does not reference another variable that could be modified in
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// the BlockStmt. It does this by checking the following:
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// 1. If the variable is neither a reference nor a pointer then the
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// isOnlyUsedAsConst() check is sufficient.
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// 2. If the (reference or pointer) variable is not initialized in a DeclStmt in
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// the BlockStmt. In this case its pointee is likely not modified (unless it
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// is passed as an alias into the method as well).
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// 3. If the reference is initialized from a reference to const. This is
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// the same set of criteria we apply when identifying the unnecessary copied
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// variable in this check to begin with. In this case we check whether the
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// object arg or variable that is referenced is immutable as well.
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static bool isInitializingVariableImmutable(const VarDecl &InitializingVar,
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const Stmt &BlockStmt,
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ASTContext &Context) {
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if (!isOnlyUsedAsConst(InitializingVar, BlockStmt, Context))
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return false;
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QualType T = InitializingVar.getType();
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// The variable is a value type and we know it is only used as const. Safe
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// to reference it and avoid the copy.
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if (!isa<ReferenceType, PointerType>(T))
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return true;
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auto Matches =
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match(findAll(declStmt(has(varDecl(equalsNode(&InitializingVar))))
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.bind("declStmt")),
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BlockStmt, Context);
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// The reference or pointer is not initialized in the BlockStmt. We assume
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// its pointee is not modified then.
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if (Matches.empty())
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return true;
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const auto *Initialization = selectFirst<DeclStmt>("declStmt", Matches);
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Matches =
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match(isInitializedFromReferenceToConst(), *Initialization, Context);
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// The reference is initialized from a free function without arguments
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// returning a const reference. This is a global immutable object.
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if (selectFirst<CallExpr>(InitFunctionCallId, Matches) != nullptr)
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return true;
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// Check that the object argument is immutable as well.
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if (const auto *OrigVar = selectFirst<VarDecl>(ObjectArgId, Matches))
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return isInitializingVariableImmutable(*OrigVar, BlockStmt, Context);
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// Check that the old variable we reference is immutable as well.
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if (const auto *OrigVar = selectFirst<VarDecl>(OldVarDeclId, Matches))
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return isInitializingVariableImmutable(*OrigVar, BlockStmt, Context);
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return false;
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}
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} // namespace
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UnnecessaryCopyInitialization::UnnecessaryCopyInitialization(
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StringRef Name, ClangTidyContext *Context)
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: ClangTidyCheck(Name, Context),
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AllowedTypes(
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utils::options::parseStringList(Options.get("AllowedTypes", ""))) {}
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void UnnecessaryCopyInitialization::registerMatchers(MatchFinder *Finder) {
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auto localVarCopiedFrom = [this](const internal::Matcher<Expr> &CopyCtorArg) {
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return compoundStmt(
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forEachDescendant(
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declStmt(
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has(varDecl(hasLocalStorage(),
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hasType(qualType(
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hasCanonicalType(allOf(
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matchers::isExpensiveToCopy(),
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unless(hasDeclaration(namedDecl(
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hasName("::std::function")))))),
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unless(hasDeclaration(namedDecl(
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matchers::matchesAnyListedName(
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AllowedTypes)))))),
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unless(isImplicit()),
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hasInitializer(traverse(
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ast_type_traits::TK_AsIs,
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cxxConstructExpr(
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hasDeclaration(cxxConstructorDecl(
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isCopyConstructor())),
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hasArgument(0, CopyCtorArg))
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.bind("ctorCall"))))
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.bind("newVarDecl")))
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.bind("declStmt")))
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.bind("blockStmt");
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};
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Finder->addMatcher(localVarCopiedFrom(anyOf(isConstRefReturningFunctionCall(),
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isConstRefReturningMethodCall())),
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this);
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Finder->addMatcher(localVarCopiedFrom(declRefExpr(
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to(varDecl(hasLocalStorage()).bind(OldVarDeclId)))),
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this);
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}
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void UnnecessaryCopyInitialization::check(
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const MatchFinder::MatchResult &Result) {
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const auto *NewVar = Result.Nodes.getNodeAs<VarDecl>("newVarDecl");
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const auto *OldVar = Result.Nodes.getNodeAs<VarDecl>(OldVarDeclId);
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const auto *ObjectArg = Result.Nodes.getNodeAs<VarDecl>(ObjectArgId);
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const auto *BlockStmt = Result.Nodes.getNodeAs<Stmt>("blockStmt");
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const auto *CtorCall = Result.Nodes.getNodeAs<CXXConstructExpr>("ctorCall");
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TraversalKindScope RAII(*Result.Context, ast_type_traits::TK_AsIs);
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// Do not propose fixes if the DeclStmt has multiple VarDecls or in macros
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// since we cannot place them correctly.
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bool IssueFix =
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Result.Nodes.getNodeAs<DeclStmt>("declStmt")->isSingleDecl() &&
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!NewVar->getLocation().isMacroID();
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// A constructor that looks like T(const T& t, bool arg = false) counts as a
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// copy only when it is called with default arguments for the arguments after
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// the first.
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for (unsigned int i = 1; i < CtorCall->getNumArgs(); ++i)
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if (!CtorCall->getArg(i)->isDefaultArgument())
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return;
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if (OldVar == nullptr) {
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handleCopyFromMethodReturn(*NewVar, *BlockStmt, IssueFix, ObjectArg,
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*Result.Context);
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} else {
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handleCopyFromLocalVar(*NewVar, *OldVar, *BlockStmt, IssueFix,
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*Result.Context);
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}
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}
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void UnnecessaryCopyInitialization::handleCopyFromMethodReturn(
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const VarDecl &Var, const Stmt &BlockStmt, bool IssueFix,
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const VarDecl *ObjectArg, ASTContext &Context) {
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bool IsConstQualified = Var.getType().isConstQualified();
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if (!IsConstQualified && !isOnlyUsedAsConst(Var, BlockStmt, Context))
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return;
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if (ObjectArg != nullptr &&
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!isInitializingVariableImmutable(*ObjectArg, BlockStmt, Context))
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return;
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auto Diagnostic =
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diag(Var.getLocation(),
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IsConstQualified ? "the const qualified variable %0 is "
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"copy-constructed from a const reference; "
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"consider making it a const reference"
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: "the variable %0 is copy-constructed from a "
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"const reference but is only used as const "
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"reference; consider making it a const reference")
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<< &Var;
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if (IssueFix)
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recordFixes(Var, Context, Diagnostic);
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}
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void UnnecessaryCopyInitialization::handleCopyFromLocalVar(
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const VarDecl &NewVar, const VarDecl &OldVar, const Stmt &BlockStmt,
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bool IssueFix, ASTContext &Context) {
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if (!isOnlyUsedAsConst(NewVar, BlockStmt, Context) ||
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!isInitializingVariableImmutable(OldVar, BlockStmt, Context))
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return;
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auto Diagnostic = diag(NewVar.getLocation(),
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"local copy %0 of the variable %1 is never modified; "
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"consider avoiding the copy")
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<< &NewVar << &OldVar;
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if (IssueFix)
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recordFixes(NewVar, Context, Diagnostic);
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}
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void UnnecessaryCopyInitialization::storeOptions(
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ClangTidyOptions::OptionMap &Opts) {
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Options.store(Opts, "AllowedTypes",
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utils::options::serializeStringList(AllowedTypes));
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}
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} // namespace performance
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} // namespace tidy
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} // namespace clang
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