Add check for unneeded copies of locals
Summary: Extends the UnnecessaryCopyInitialization to detect copies of local variables and parameters that are unneeded.
Patch by Matt Kulukundis!
Reviewers: alexfh, hokein
Subscribers: cfe-commits
Differential Revision: http://reviews.llvm.org/D18149
llvm-svn: 264146
diff --git a/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp b/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
index ed37b32..3fe13bc 100644
--- a/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
+++ b/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp
@@ -16,16 +16,32 @@
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(
- ast_matchers::MatchFinder *Finder) {
+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.
@@ -37,45 +53,82 @@
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(
- compoundStmt(
- forEachDescendant(
- varDecl(
- hasLocalStorage(), hasType(matchers::isExpensiveToCopy()),
- hasInitializer(cxxConstructExpr(
- hasDeclaration(cxxConstructorDecl(isCopyConstructor())),
- hasArgument(
- 0, anyOf(ConstRefReturningFunctionCall,
- ConstRefReturningMethodCallOfConstParam)))))
- .bind("varDecl"))).bind("blockStmt"),
+ localVarCopiedFrom(anyOf(ConstRefReturningFunctionCall,
+ ConstRefReturningMethodCallOfConstParam)),
this);
+
+ Finder->addMatcher(localVarCopiedFrom(declRefExpr(
+ to(varDecl(hasLocalStorage()).bind("oldVarDecl")))),
+ this);
}
void UnnecessaryCopyInitialization::check(
- const ast_matchers::MatchFinder::MatchResult &Result) {
- const auto *Var = Result.Nodes.getNodeAs<VarDecl>("varDecl");
+ 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");
- bool IsConstQualified = Var->getType().isConstQualified();
- if (!IsConstQualified &&
- !decl_ref_expr_utils::isOnlyUsedAsConst(*Var, *BlockStmt,
- *Result.Context))
+ 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;
- DiagnosticBuilder Diagnostic =
- diag(Var->getLocation(),
- IsConstQualified ? "the const qualified variable '%0' is "
+
+ 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 "
+ : "the variable %0 is copy-constructed from a "
"const reference but is only used as const "
"reference; consider making it a const reference")
- << Var->getName();
- // Do not propose fixes in macros since we cannot place them correctly.
- if (Var->getLocStart().isMacroID())
+ << &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;
- Diagnostic << utils::create_fix_it::changeVarDeclToReference(*Var,
- *Result.Context);
- if (!IsConstQualified)
- Diagnostic << utils::create_fix_it::changeVarDeclToConst(*Var);
+
+ 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