flx created this revision.
flx added reviewers: aaron.ballman, hokein.
Herald added subscribers: cfe-commits, xazax.hun.
Herald added a project: clang.
flx requested review of this revision.
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.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D91893
Files:
clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
clang-tools-extra/clang-tidy/utils/DeclRefExprUtils.cpp
clang-tools-extra/clang-tidy/utils/Matchers.h
clang-tools-extra/test/clang-tidy/checkers/performance-unnecessary-copy-initialization.cpp
Index: clang-tools-extra/test/clang-tidy/checkers/performance-unnecessary-copy-initialization.cpp
===================================================================
--- clang-tools-extra/test/clang-tidy/checkers/performance-unnecessary-copy-initialization.cpp
+++ clang-tools-extra/test/clang-tidy/checkers/performance-unnecessary-copy-initialization.cpp
@@ -476,3 +476,17 @@
auto Copy = Orig.reference();
Update(Copy);
}
+
+void negativeCopiedFromReferenceToModifiedVar() {
+ ExpensiveToCopyType Orig;
+ const auto &Ref = Orig;
+ const auto NecessaryCopy = Ref;
+ Orig.nonConstMethod();
+}
+
+void negativeCopiedFromGetterOfReferenceToModifiedVar() {
+ ExpensiveToCopyType Orig;
+ const auto &Ref = Orig.reference();
+ const auto NecessaryCopy = Ref.reference();
+ Orig.nonConstMethod();
+}
Index: clang-tools-extra/clang-tidy/utils/Matchers.h
===================================================================
--- clang-tools-extra/clang-tidy/utils/Matchers.h
+++ clang-tools-extra/clang-tidy/utils/Matchers.h
@@ -43,6 +43,12 @@
return referenceType(pointee(qualType(isConstQualified())));
}
+// Returns QualType matcher for pointers to const.
+AST_MATCHER_FUNCTION(ast_matchers::TypeMatcher, isPointerToConst) {
+ using namespace ast_matchers;
+ return pointerType(pointee(qualType(isConstQualified())));
+}
+
AST_MATCHER_P(NamedDecl, matchesAnyListedName, std::vector<std::string>,
NameList) {
return llvm::any_of(NameList, [&Node](const std::string &Name) {
Index: clang-tools-extra/clang-tidy/utils/DeclRefExprUtils.cpp
===================================================================
--- clang-tools-extra/clang-tidy/utils/DeclRefExprUtils.cpp
+++ clang-tools-extra/clang-tidy/utils/DeclRefExprUtils.cpp
@@ -58,7 +58,7 @@
SmallPtrSet<const DeclRefExpr *, 16> DeclRefs;
extractNodesByIdTo(Matches, "declRef", DeclRefs);
auto ConstReferenceOrValue =
- qualType(anyOf(referenceType(pointee(qualType(isConstQualified()))),
+ qualType(anyOf(matchers::isReferenceToConst(),
unless(anyOf(referenceType(), pointerType(),
substTemplateTypeParmType()))));
auto ConstReferenceOrValueOrReplaced = qualType(anyOf(
@@ -71,6 +71,20 @@
Matches =
match(findAll(cxxConstructExpr(UsedAsConstRefOrValueArg)), Stmt, Context);
extractNodesByIdTo(Matches, "declRef", DeclRefs);
+ // References and pointers to const assignments.
+ Matches =
+ match(findAll(declStmt(
+ has(varDecl(hasType(qualType(matchers::isReferenceToConst())),
+ hasInitializer(ignoringImpCasts(DeclRefToVar)))))),
+ Stmt, Context);
+ extractNodesByIdTo(Matches, "declRef", DeclRefs);
+ Matches =
+ match(findAll(declStmt(has(varDecl(
+ hasType(qualType(matchers::isPointerToConst())),
+ hasInitializer(ignoringImpCasts(unaryOperator(
+ hasOperatorName("&"), hasUnaryOperand(DeclRefToVar)))))))),
+ Stmt, Context);
+ extractNodesByIdTo(Matches, "declRef", DeclRefs);
return DeclRefs;
}
Index: clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
===================================================================
--- clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
+++ clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
@@ -7,7 +7,6 @@
//===----------------------------------------------------------------------===//
#include "UnnecessaryCopyInitialization.h"
-
#include "../utils/DeclRefExprUtils.h"
#include "../utils/FixItHintUtils.h"
#include "../utils/Matchers.h"
@@ -19,6 +18,14 @@
namespace performance {
namespace {
+using namespace ::clang::ast_matchers;
+using llvm::StringRef;
+using utils::decl_ref_expr::isOnlyUsedAsConst;
+
+static constexpr StringRef kObjectArg = "objectArg";
+static constexpr StringRef kInitFunctionCall = "initFunctionCall";
+static constexpr StringRef kOldVarDecl = "oldVarDecl";
+
void recordFixes(const VarDecl &Var, ASTContext &Context,
DiagnosticBuilder &Diagnostic) {
Diagnostic << utils::fixit::changeVarDeclToReference(Var, Context);
@@ -29,10 +36,91 @@
}
}
-} // namespace
+AST_MATCHER_FUNCTION(StatementMatcher, isConstRefReturningMethodCall) {
+ // Match method call expressions where the `this` argument is only used as
+ // const, this will be checked in `check()` part. 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.
+ return cxxMemberCallExpr(
+ callee(cxxMethodDecl(returns(matchers::isReferenceToConst()))),
+ on(declRefExpr(to(varDecl().bind(kObjectArg)))));
+}
-using namespace ::clang::ast_matchers;
-using utils::decl_ref_expr::isOnlyUsedAsConst;
+AST_MATCHER_FUNCTION(StatementMatcher, isConstRefReturningFunctionCall) {
+ // Only allow initialization of a const reference from a free function if it
+ // has no arguments. Otherwise it could return an alias to one of its
+ // arguments and the arguments need to be checked for const use as well.
+ return callExpr(callee(functionDecl(returns(matchers::isReferenceToConst()))),
+ argumentCountIs(0), unless(callee(cxxMethodDecl())))
+ .bind(kInitFunctionCall);
+}
+
+AST_MATCHER_FUNCTION(StatementMatcher, isInitializedFromReferenceToConst) {
+ auto OldVarDeclRef =
+ declRefExpr(to(varDecl(hasLocalStorage()).bind(kOldVarDecl)));
+ return declStmt(has(varDecl(hasInitializer(
+ anyOf(isConstRefReturningFunctionCall(), isConstRefReturningMethodCall(),
+ ignoringImpCasts(OldVarDeclRef),
+ ignoringImpCasts(unaryOperator(
+ hasOperatorName("&"), hasUnaryOperand(OldVarDeclRef))))))));
+}
+
+// This checks that the variable itself is only used as const, and also makes
+// sure that it does not reference another variable that could be modified in
+// the BlockStmt. It does this by checking the following:
+// 1. If the variable is neither a reference nor a pointer then the the
+// isOnlyUsedAsConst() check is sufficient.
+// 2. If the (reference or pointer) variable is not initialized in a DeclStmt in
+// the BlockStmt. In this case it its pointee is likely not modified (unless it
+// is passed as an alias into the method as well).
+// 3. If the reference is initialized from a reference to const. This is
+// the same set of criteria we apply when identifying the unnecessary copied
+// variable in this check to begin with. In this case we check whether the
+// object arg or variable that is referenced is immutable as well.
+bool isInitializingVariableImmutable(const VarDecl &InitializingVar,
+ const Stmt &BlockStmt,
+ ASTContext &Context) {
+ if (!isOnlyUsedAsConst(InitializingVar, BlockStmt, Context)) {
+ return false;
+ }
+ QualType type = InitializingVar.getType();
+ if (!llvm::dyn_cast<ReferenceType>(type) &&
+ !llvm::dyn_cast<PointerType>(type)) {
+ // The variable is a value type and we know it is only used as const. Safe
+ // to reference it and avoid the copy.
+ return true;
+ }
+ auto Matches =
+ match(findAll(declStmt(has(varDecl(equalsNode(&InitializingVar))))
+ .bind("declStmt")),
+ BlockStmt, Context);
+ if (Matches.empty()) {
+ // The reference or pointer is not initialized in the BlockStmt. We assume
+ // its pointee is not modified then.
+ return true;
+ }
+ const auto *Initialization = selectFirst<DeclStmt>("declStmt", Matches);
+ Matches =
+ match(isInitializedFromReferenceToConst(), *Initialization, Context);
+ if (selectFirst<CallExpr>(kInitFunctionCall, Matches) != nullptr) {
+ // The reference is initialized from a free function without arguments
+ // returning a const reference. This must be an immutable.
+ return true;
+ }
+ if (const auto *OrigVar = selectFirst<VarDecl>(kObjectArg, Matches)) {
+ // Check that the object argument is immutable as well.
+ return isInitializingVariableImmutable(*OrigVar, BlockStmt, Context);
+ }
+ if (const auto *OrigVar = selectFirst<VarDecl>(kOldVarDecl, Matches)) {
+ // Check that the old variable we reference is immutable as well.
+ return isInitializingVariableImmutable(*OrigVar, BlockStmt, Context);
+ }
+ return false;
+}
+
+} // namespace
UnnecessaryCopyInitialization::UnnecessaryCopyInitialization(
StringRef Name, ClangTidyContext *Context)
@@ -41,22 +129,6 @@
utils::options::parseStringList(Options.get("AllowedTypes", ""))) {}
void UnnecessaryCopyInitialization::registerMatchers(MatchFinder *Finder) {
- auto ConstReference = referenceType(pointee(qualType(isConstQualified())));
-
- // Match method call expressions where the `this` argument is only used as
- // const, this will be checked in `check()` part. 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 ConstRefReturningMethodCall =
- cxxMemberCallExpr(callee(cxxMethodDecl(returns(ConstReference))),
- on(declRefExpr(to(varDecl().bind("objectArg")))));
- auto ConstRefReturningFunctionCall =
- callExpr(callee(functionDecl(returns(ConstReference))),
- unless(callee(cxxMethodDecl())))
- .bind("initFunctionCall");
-
auto localVarCopiedFrom = [this](const internal::Matcher<Expr> &CopyCtorArg) {
return compoundStmt(
forEachDescendant(
@@ -83,24 +155,22 @@
.bind("blockStmt");
};
- Finder->addMatcher(localVarCopiedFrom(anyOf(ConstRefReturningFunctionCall,
- ConstRefReturningMethodCall)),
+ Finder->addMatcher(localVarCopiedFrom(anyOf(isConstRefReturningFunctionCall(),
+ isConstRefReturningMethodCall())),
this);
Finder->addMatcher(localVarCopiedFrom(declRefExpr(
- to(varDecl(hasLocalStorage()).bind("oldVarDecl")))),
+ to(varDecl(hasLocalStorage()).bind(kOldVarDecl)))),
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 *ObjectArg = Result.Nodes.getNodeAs<VarDecl>("objectArg");
+ const auto *OldVar = Result.Nodes.getNodeAs<VarDecl>(kOldVarDecl);
+ const auto *ObjectArg = Result.Nodes.getNodeAs<VarDecl>(kObjectArg);
const auto *BlockStmt = Result.Nodes.getNodeAs<Stmt>("blockStmt");
const auto *CtorCall = Result.Nodes.getNodeAs<CXXConstructExpr>("ctorCall");
- const auto *InitFunctionCall =
- Result.Nodes.getNodeAs<CallExpr>("initFunctionCall");
TraversalKindScope RAII(*Result.Context, ast_type_traits::TK_AsIs);
@@ -118,11 +188,6 @@
return;
if (OldVar == nullptr) {
- // Only allow initialization of a const reference from a free function if it
- // has no arguments. Otherwise it could return an alias to one of its
- // arguments and the arguments need to be checked for const use as well.
- if (InitFunctionCall != nullptr && InitFunctionCall->getNumArgs() > 0)
- return;
handleCopyFromMethodReturn(*NewVar, *BlockStmt, IssueFix, ObjectArg,
*Result.Context);
} else {
@@ -138,7 +203,7 @@
if (!IsConstQualified && !isOnlyUsedAsConst(Var, BlockStmt, Context))
return;
if (ObjectArg != nullptr &&
- !isOnlyUsedAsConst(*ObjectArg, BlockStmt, Context))
+ !isInitializingVariableImmutable(*ObjectArg, BlockStmt, Context))
return;
auto Diagnostic =
@@ -158,7 +223,7 @@
const VarDecl &NewVar, const VarDecl &OldVar, const Stmt &BlockStmt,
bool IssueFix, ASTContext &Context) {
if (!isOnlyUsedAsConst(NewVar, BlockStmt, Context) ||
- !isOnlyUsedAsConst(OldVar, BlockStmt, Context))
+ !isInitializingVariableImmutable(OldVar, BlockStmt, Context))
return;
auto Diagnostic = diag(NewVar.getLocation(),
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