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//===--- UnnecessaryCopyInitialization.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 "UnnecessaryCopyInitialization.h"
#include "../utils/DeclRefExprUtils.h"
#include "../utils/FixItHintUtils.h"
#include "../utils/Matchers.h"
namespace clang {
namespace tidy {
namespace performance {
namespace {
void recordFixes(const VarDecl &Var, ASTContext &Context,
DiagnosticBuilder &Diagnostic) {
// Do not propose fixes in macros since we cannot place them correctly.
if (Var.getLocation().isMacroID())
return;
Diagnostic << utils::create_fix_it::changeVarDeclToReference(Var, Context);
if (!Var.getType().isLocalConstQualified())
Diagnostic << utils::create_fix_it::changeVarDeclToConst(Var);
}
} // namespace
using namespace ::clang::ast_matchers;
using decl_ref_expr_utils::isOnlyUsedAsConst;
void UnnecessaryCopyInitialization::registerMatchers(MatchFinder *Finder) {
auto ConstReference = referenceType(pointee(qualType(isConstQualified())));
auto ConstOrConstReference =
allOf(anyOf(ConstReference, isConstQualified()),
unless(allOf(pointerType(), unless(pointerType(pointee(
qualType(isConstQualified())))))));
// Match method call expressions where the this argument is a const
// type or const reference. This returned const reference is highly likely to
// outlive the local const reference of the variable being declared.
// The assumption is that the const reference being returned either points
// to a global static variable or to a member of the called object.
auto ConstRefReturningMethodCallOfConstParam = cxxMemberCallExpr(
callee(cxxMethodDecl(returns(ConstReference))),
on(declRefExpr(to(varDecl(hasType(qualType(ConstOrConstReference)))))));
auto ConstRefReturningFunctionCall =
callExpr(callee(functionDecl(returns(ConstReference))),
unless(callee(cxxMethodDecl())));
auto localVarCopiedFrom = [](const internal::Matcher<Expr> &CopyCtorArg) {
return compoundStmt(
forEachDescendant(
varDecl(hasLocalStorage(),
hasType(matchers::isExpensiveToCopy()),
hasInitializer(cxxConstructExpr(
hasDeclaration(cxxConstructorDecl(
isCopyConstructor())),
hasArgument(0, CopyCtorArg))
.bind("ctorCall")))
.bind("newVarDecl")))
.bind("blockStmt");
};
Finder->addMatcher(
localVarCopiedFrom(anyOf(ConstRefReturningFunctionCall,
ConstRefReturningMethodCallOfConstParam)),
this);
Finder->addMatcher(localVarCopiedFrom(declRefExpr(
to(varDecl(hasLocalStorage()).bind("oldVarDecl")))),
this);
}
void UnnecessaryCopyInitialization::check(
const MatchFinder::MatchResult &Result) {
const auto *NewVar = Result.Nodes.getNodeAs<VarDecl>("newVarDecl");
const auto *OldVar = Result.Nodes.getNodeAs<VarDecl>("oldVarDecl");
const auto *BlockStmt = Result.Nodes.getNodeAs<Stmt>("blockStmt");
const auto *CtorCall = Result.Nodes.getNodeAs<CXXConstructExpr>("ctorCall");
// A constructor that looks like T(const T& t, bool arg = false) counts as a
// copy only when it is called with default arguments for the arguments after
// the first.
for (unsigned int i = 1; i < CtorCall->getNumArgs(); ++i)
if (!CtorCall->getArg(i)->isDefaultArgument())
return;
if (OldVar == nullptr) {
handleCopyFromMethodReturn(*NewVar, *BlockStmt, *Result.Context);
} else {
handleCopyFromLocalVar(*NewVar, *OldVar, *BlockStmt, *Result.Context);
}
}
void UnnecessaryCopyInitialization::handleCopyFromMethodReturn(
const VarDecl &Var, const Stmt &BlockStmt, ASTContext &Context) {
bool IsConstQualified = Var.getType().isConstQualified();
if (!IsConstQualified && !isOnlyUsedAsConst(Var, BlockStmt, Context))
return;
auto Diagnostic =
diag(Var.getLocation(),
IsConstQualified ? "the const qualified variable %0 is "
"copy-constructed from a const reference; "
"consider making it a const reference"
: "the variable %0 is copy-constructed from a "
"const reference but is only used as const "
"reference; consider making it a const reference")
<< &Var;
recordFixes(Var, Context, Diagnostic);
}
void UnnecessaryCopyInitialization::handleCopyFromLocalVar(
const VarDecl &NewVar, const VarDecl &OldVar, const Stmt &BlockStmt,
ASTContext &Context) {
if (!isOnlyUsedAsConst(NewVar, BlockStmt, Context) ||
!isOnlyUsedAsConst(OldVar, BlockStmt, Context))
return;
auto Diagnostic = diag(NewVar.getLocation(),
"local copy %0 of the variable %1 is never modified; "
"consider avoiding the copy")
<< &NewVar << &OldVar;
recordFixes(NewVar, Context, Diagnostic);
}
} // namespace performance
} // namespace tidy
} // namespace clang
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