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//===--- UnnecessaryValueParamCheck.cpp - clang-tidy-----------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "UnnecessaryValueParamCheck.h"
#include "../utils/DeclRefExprUtils.h"
#include "../utils/FixItHintUtils.h"
#include "../utils/Matchers.h"
#include "../utils/TypeTraits.h"
#include "clang/Frontend/CompilerInstance.h"
#include "clang/Lex/Lexer.h"
#include "clang/Lex/Preprocessor.h"
using namespace clang::ast_matchers;
namespace clang {
namespace tidy {
namespace 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();
}
template <typename S>
bool isSubset(const S &SubsetCandidate, const S &SupersetCandidate) {
for (const auto &E : SubsetCandidate)
if (SupersetCandidate.count(E) == 0)
return false;
return true;
}
} // namespace
UnnecessaryValueParamCheck::UnnecessaryValueParamCheck(
StringRef Name, ClangTidyContext *Context)
: ClangTidyCheck(Name, Context),
IncludeStyle(utils::IncludeSorter::parseIncludeStyle(
Options.get("IncludeStyle", "llvm"))) {}
void UnnecessaryValueParamCheck::registerMatchers(MatchFinder *Finder) {
const auto ExpensiveValueParamDecl =
parmVarDecl(hasType(hasCanonicalType(allOf(matchers::isExpensiveToCopy(),
unless(referenceType())))),
decl().bind("param"));
Finder->addMatcher(
functionDecl(isDefinition(), unless(cxxMethodDecl(isOverride())),
unless(isInstantiated()),
has(typeLoc(forEach(ExpensiveValueParamDecl))),
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");
const size_t Index = std::find(Function->parameters().begin(),
Function->parameters().end(), Param) -
Function->parameters().begin();
bool IsConstQualified =
Param->getType().getCanonicalType().isConstQualified();
// Skip declarations delayed by late template parsing without a body.
if (!Function->getBody())
return;
// Do not trigger on non-const value parameters when:
// 1. they are in a constructor definition since they can likely trigger
// misc-move-constructor-init which will suggest to move the argument.
if (!IsConstQualified && (llvm::isa<CXXConstructorDecl>(Function) ||
!Function->doesThisDeclarationHaveABody()))
return;
auto AllDeclRefExprs = utils::decl_ref_expr::allDeclRefExprs(
*Param, *Function->getBody(), *Result.Context);
auto ConstDeclRefExprs = utils::decl_ref_expr::constReferenceDeclRefExprs(
*Param, *Function->getBody(), *Result.Context);
// 2. they are not only used as const.
if (!isSubset(AllDeclRefExprs, ConstDeclRefExprs))
return;
// 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 CanonicalType = Param->getType().getCanonicalType();
if (AllDeclRefExprs.size() == 1 &&
((utils::type_traits::hasNonTrivialMoveConstructor(CanonicalType) &&
utils::decl_ref_expr::isCopyConstructorArgument(
**AllDeclRefExprs.begin(), *Function->getBody(),
*Result.Context)) ||
(utils::type_traits::hasNonTrivialMoveAssignment(CanonicalType) &&
utils::decl_ref_expr::isCopyAssignmentArgument(
**AllDeclRefExprs.begin(), *Function->getBody(),
*Result.Context)))) {
handleMoveFix(*Param, **AllDeclRefExprs.begin(), *Result.Context);
return;
}
}
auto Diag =
diag(Param->getLocation(),
IsConstQualified ? "the const qualified parameter %0 is "
"copied for each invocation; consider "
"making it a reference"
: "the parameter %0 is copied for each "
"invocation but only used as a const reference; "
"consider making it a const reference")
<< paramNameOrIndex(Param->getName(), Index);
// Do not propose fixes in macros since we cannot place them correctly, or if
// function is virtual as it might break overrides.
const auto *Method = llvm::dyn_cast<CXXMethodDecl>(Function);
if (Param->getLocStart().isMacroID() || (Method && Method->isVirtual()))
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())
Diag << utils::fixit::changeVarDeclToConst(CurrentParam);
}
}
void UnnecessaryValueParamCheck::registerPPCallbacks(
CompilerInstance &Compiler) {
Inserter.reset(new utils::IncludeInserter(
Compiler.getSourceManager(), Compiler.getLangOpts(), IncludeStyle));
Compiler.getPreprocessor().addPPCallbacks(Inserter->CreatePPCallbacks());
}
void UnnecessaryValueParamCheck::storeOptions(
ClangTidyOptions::OptionMap &Opts) {
Options.store(Opts, "IncludeStyle",
utils::IncludeSorter::toString(IncludeStyle));
}
void UnnecessaryValueParamCheck::handleMoveFix(const ParmVarDecl &Var,
const DeclRefExpr &CopyArgument,
const ASTContext &Context) {
auto Diag = diag(CopyArgument.getLocStart(),
"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.getLocStart().isMacroID())
return;
const auto &SM = Context.getSourceManager();
auto EndLoc = Lexer::getLocForEndOfToken(CopyArgument.getLocation(), 0, SM,
Context.getLangOpts());
Diag << FixItHint::CreateInsertion(CopyArgument.getLocStart(), "std::move(")
<< FixItHint::CreateInsertion(EndLoc, ")");
if (auto IncludeFixit = Inserter->CreateIncludeInsertion(
SM.getFileID(CopyArgument.getLocStart()), "utility",
/*IsAngled=*/true))
Diag << *IncludeFixit;
}
} // namespace performance
} // namespace tidy
} // namespace clang
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