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//===--- UnnecessaryValueParamCheck.cpp - clang-tidy-----------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "UnnecessaryValueParamCheck.h"
#include "../utils/DeclRefExprUtils.h"
#include "../utils/FixItHintUtils.h"
#include "../utils/Matchers.h"
#include "../utils/OptionsUtils.h"
#include "../utils/TypeTraits.h"
#include "clang/Frontend/CompilerInstance.h"
#include "clang/Lex/Lexer.h"
#include "clang/Lex/Preprocessor.h"
#include <optional>
using namespace clang::ast_matchers;
namespace clang::tidy::performance {
namespace {
std::string paramNameOrIndex(StringRef Name, size_t Index) {
return (Name.empty() ? llvm::Twine('#') + llvm::Twine(Index + 1)
: llvm::Twine('\'') + Name + llvm::Twine('\''))
.str();
}
bool isReferencedOutsideOfCallExpr(const FunctionDecl &Function,
ASTContext &Context) {
auto Matches = match(declRefExpr(to(functionDecl(equalsNode(&Function))),
unless(hasAncestor(callExpr()))),
Context);
return !Matches.empty();
}
bool hasLoopStmtAncestor(const DeclRefExpr &DeclRef, const Decl &Decl,
ASTContext &Context) {
auto Matches = match(
traverse(TK_AsIs,
decl(forEachDescendant(declRefExpr(
equalsNode(&DeclRef),
unless(hasAncestor(stmt(anyOf(forStmt(), cxxForRangeStmt(),
whileStmt(), doStmt())))))))),
Decl, Context);
return Matches.empty();
}
} // namespace
UnnecessaryValueParamCheck::UnnecessaryValueParamCheck(
StringRef Name, ClangTidyContext *Context)
: ClangTidyCheck(Name, Context),
Inserter(Options.getLocalOrGlobal("IncludeStyle",
utils::IncludeSorter::IS_LLVM),
areDiagsSelfContained()),
AllowedTypes(
utils::options::parseStringList(Options.get("AllowedTypes", ""))) {}
void UnnecessaryValueParamCheck::registerMatchers(MatchFinder *Finder) {
const auto ExpensiveValueParamDecl = parmVarDecl(
hasType(qualType(
hasCanonicalType(matchers::isExpensiveToCopy()),
unless(anyOf(hasCanonicalType(referenceType()),
hasDeclaration(namedDecl(
matchers::matchesAnyListedName(AllowedTypes))))))),
decl().bind("param"));
Finder->addMatcher(
traverse(
TK_AsIs,
functionDecl(hasBody(stmt()), isDefinition(), unless(isImplicit()),
unless(cxxMethodDecl(anyOf(isOverride(), isFinal()))),
has(typeLoc(forEach(ExpensiveValueParamDecl))),
unless(isInstantiated()), decl().bind("functionDecl"))),
this);
}
void UnnecessaryValueParamCheck::check(const MatchFinder::MatchResult &Result) {
const auto *Param = Result.Nodes.getNodeAs<ParmVarDecl>("param");
const auto *Function = Result.Nodes.getNodeAs<FunctionDecl>("functionDecl");
TraversalKindScope RAII(*Result.Context, TK_AsIs);
FunctionParmMutationAnalyzer &Analyzer =
MutationAnalyzers.try_emplace(Function, *Function, *Result.Context)
.first->second;
if (Analyzer.isMutated(Param))
return;
const bool IsConstQualified =
Param->getType().getCanonicalType().isConstQualified();
// If the parameter is non-const, check if it has a move constructor and is
// only referenced once to copy-construct another object or whether it has a
// move assignment operator and is only referenced once when copy-assigned.
// In this case wrap DeclRefExpr with std::move() to avoid the unnecessary
// copy.
if (!IsConstQualified) {
auto AllDeclRefExprs = utils::decl_ref_expr::allDeclRefExprs(
*Param, *Function, *Result.Context);
if (AllDeclRefExprs.size() == 1) {
auto CanonicalType = Param->getType().getCanonicalType();
const auto &DeclRefExpr = **AllDeclRefExprs.begin();
if (!hasLoopStmtAncestor(DeclRefExpr, *Function, *Result.Context) &&
((utils::type_traits::hasNonTrivialMoveConstructor(CanonicalType) &&
utils::decl_ref_expr::isCopyConstructorArgument(
DeclRefExpr, *Function, *Result.Context)) ||
(utils::type_traits::hasNonTrivialMoveAssignment(CanonicalType) &&
utils::decl_ref_expr::isCopyAssignmentArgument(
DeclRefExpr, *Function, *Result.Context)))) {
handleMoveFix(*Param, DeclRefExpr, *Result.Context);
return;
}
}
}
const size_t Index = llvm::find(Function->parameters(), Param) -
Function->parameters().begin();
auto Diag =
diag(Param->getLocation(),
"the %select{|const qualified }0parameter %1 is copied for each "
"invocation%select{ but only used as a const reference|}0; consider "
"making it a %select{const |}0reference")
<< IsConstQualified << paramNameOrIndex(Param->getName(), Index);
// Do not propose fixes when:
// 1. the ParmVarDecl is in a macro, since we cannot place them correctly
// 2. the function is virtual as it might break overrides
// 3. the function is referenced outside of a call expression within the
// compilation unit as the signature change could introduce build errors.
// 4. the function is a primary template or an explicit template
// specialization.
const auto *Method = llvm::dyn_cast<CXXMethodDecl>(Function);
if (Param->getBeginLoc().isMacroID() || (Method && Method->isVirtual()) ||
isReferencedOutsideOfCallExpr(*Function, *Result.Context) ||
(Function->getTemplatedKind() != FunctionDecl::TK_NonTemplate))
return;
for (const auto *FunctionDecl = Function; FunctionDecl != nullptr;
FunctionDecl = FunctionDecl->getPreviousDecl()) {
const auto &CurrentParam = *FunctionDecl->getParamDecl(Index);
Diag << utils::fixit::changeVarDeclToReference(CurrentParam,
*Result.Context);
// The parameter of each declaration needs to be checked individually as to
// whether it is const or not as constness can differ between definition and
// declaration.
if (!CurrentParam.getType().getCanonicalType().isConstQualified()) {
if (std::optional<FixItHint> Fix = utils::fixit::addQualifierToVarDecl(
CurrentParam, *Result.Context, DeclSpec::TQ::TQ_const))
Diag << *Fix;
}
}
}
void UnnecessaryValueParamCheck::registerPPCallbacks(
const SourceManager &SM, Preprocessor *PP, Preprocessor *ModuleExpanderPP) {
Inserter.registerPreprocessor(PP);
}
void UnnecessaryValueParamCheck::storeOptions(
ClangTidyOptions::OptionMap &Opts) {
Options.store(Opts, "IncludeStyle", Inserter.getStyle());
Options.store(Opts, "AllowedTypes",
utils::options::serializeStringList(AllowedTypes));
}
void UnnecessaryValueParamCheck::onEndOfTranslationUnit() {
MutationAnalyzers.clear();
}
void UnnecessaryValueParamCheck::handleMoveFix(const ParmVarDecl &Var,
const DeclRefExpr &CopyArgument,
const ASTContext &Context) {
auto Diag = diag(CopyArgument.getBeginLoc(),
"parameter %0 is passed by value and only copied once; "
"consider moving it to avoid unnecessary copies")
<< &Var;
// Do not propose fixes in macros since we cannot place them correctly.
if (CopyArgument.getBeginLoc().isMacroID())
return;
const auto &SM = Context.getSourceManager();
auto EndLoc = Lexer::getLocForEndOfToken(CopyArgument.getLocation(), 0, SM,
Context.getLangOpts());
Diag << FixItHint::CreateInsertion(CopyArgument.getBeginLoc(), "std::move(")
<< FixItHint::CreateInsertion(EndLoc, ")")
<< Inserter.createIncludeInsertion(
SM.getFileID(CopyArgument.getBeginLoc()), "<utility>");
}
} // namespace clang::tidy::performance
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