[clang-tidy] Add check performance-lost-std-move #139525

segoon · 2025-05-12T10:08:36Z

No description provided.

llvmbot · 2025-05-12T10:09:10Z

@llvm/pr-subscribers-clang-tools-extra

Author: Vasiliy Kulikov (segoon)

Changes

Full diff: https://github.com/llvm/llvm-project/pull/139525.diff

8 Files Affected:

(modified) clang-tools-extra/clang-tidy/performance/CMakeLists.txt (+1)
(added) clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp (+96)
(added) clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.h (+37)
(modified) clang-tools-extra/clang-tidy/performance/PerformanceTidyModule.cpp (+2)
(modified) clang-tools-extra/docs/ReleaseNotes.rst (+5)
(modified) clang-tools-extra/docs/clang-tidy/checks/list.rst (+1)
(added) clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst (+14)
(added) clang-tools-extra/test/clang-tidy/checkers/performance/lost-std-move.cpp (+108)

diff --git a/clang-tools-extra/clang-tidy/performance/CMakeLists.txt b/clang-tools-extra/clang-tidy/performance/CMakeLists.txt
index 81128ff086021..333abd10a583a 100644
--- a/clang-tools-extra/clang-tidy/performance/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/performance/CMakeLists.txt
@@ -12,6 +12,7 @@ add_clang_library(clangTidyPerformanceModule
   InefficientAlgorithmCheck.cpp
   InefficientStringConcatenationCheck.cpp
   InefficientVectorOperationCheck.cpp
+  LostStdMoveCheck.cpp
   MoveConstArgCheck.cpp
   MoveConstructorInitCheck.cpp
   NoAutomaticMoveCheck.cpp
diff --git a/clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp b/clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp
new file mode 100644
index 0000000000000..26148e1d26de9
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp
@@ -0,0 +1,96 @@
+//===--- LostStdMoveCheck.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 "LostStdMoveCheck.h"
+#include "../utils/DeclRefExprUtils.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::performance {
+
+using utils::decl_ref_expr::allDeclRefExprs;
+
+AST_MATCHER(CXXRecordDecl, hasTrivialMoveConstructor) {
+  return Node.hasDefinition() && Node.hasTrivialMoveConstructor();
+}
+
+void LostStdMoveCheck::registerMatchers(MatchFinder *Finder) {
+  auto returnParent =
+      hasParent(expr(hasParent(cxxConstructExpr(hasParent(returnStmt())))));
+
+  Finder->addMatcher(
+      declRefExpr(
+          // not "return x;"
+          unless(returnParent),
+
+          unless(hasType(namedDecl(hasName("::std::string_view")))),
+
+          // non-trivial type
+          hasType(hasCanonicalType(hasDeclaration(cxxRecordDecl()))),
+
+          // non-trivial X(X&&)
+          unless(hasType(hasCanonicalType(
+              hasDeclaration(cxxRecordDecl(hasTrivialMoveConstructor()))))),
+
+          // Not in a cycle
+          unless(hasAncestor(forStmt())), unless(hasAncestor(doStmt())),
+          unless(hasAncestor(whileStmt())),
+
+          // only non-X&
+          unless(hasDeclaration(
+              varDecl(hasType(qualType(lValueReferenceType()))))),
+
+          hasDeclaration(
+              varDecl(hasAncestor(functionDecl().bind("func"))).bind("decl")),
+
+          hasParent(expr(hasParent(cxxConstructExpr())).bind("use_parent")))
+          .bind("use"),
+      this);
+}
+
+const Expr *LostStdMoveCheck::getLastVarUsage(const VarDecl &Var,
+                                              const Decl &Func,
+                                              ASTContext &Context) {
+  auto Exprs = allDeclRefExprs(Var, Func, Context);
+
+  const Expr *LastExpr = nullptr;
+  for (const auto &Expr : Exprs) {
+    if (!LastExpr)
+      LastExpr = Expr;
+
+    if (LastExpr->getBeginLoc() < Expr->getBeginLoc())
+      LastExpr = Expr;
+  }
+
+  return LastExpr;
+}
+
+void LostStdMoveCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *MatchedDecl = Result.Nodes.getNodeAs<VarDecl>("decl");
+  const auto *MatchedFunc = Result.Nodes.getNodeAs<FunctionDecl>("func");
+  const auto *MatchedUse = Result.Nodes.getNodeAs<Expr>("use");
+  const auto *MatchedUseCall = Result.Nodes.getNodeAs<CallExpr>("use_parent");
+
+  if (MatchedUseCall)
+    return;
+
+  const auto *LastUsage =
+      getLastVarUsage(*MatchedDecl, *MatchedFunc, *Result.Context);
+  if (LastUsage == nullptr)
+    return;
+
+  if (LastUsage->getBeginLoc() > MatchedUse->getBeginLoc()) {
+    // "use" is not the last reference to x
+    return;
+  }
+
+  diag(LastUsage->getBeginLoc(), "Could be std::move()");
+}
+
+} // namespace clang::tidy::performance
diff --git a/clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.h b/clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.h
new file mode 100644
index 0000000000000..c62c3f6448a82
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.h
@@ -0,0 +1,37 @@
+//===--- LostStdMoveCheck.h - clang-tidy ------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PERFORMANCE_LOSTSTDMOVECHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PERFORMANCE_LOSTSTDMOVECHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::performance {
+
+/// Search for lost std::move().
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/performance/lost-std-move.html
+class LostStdMoveCheck : public ClangTidyCheck {
+public:
+  LostStdMoveCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.CPlusPlus;
+  }
+
+private:
+  const Expr *getLastVarUsage(const VarDecl &Var, const Decl &Func,
+                              ASTContext &Context);
+};
+
+} // namespace clang::tidy::performance
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PERFORMANCE_LOSTSTDMOVECHECK_H
diff --git a/clang-tools-extra/clang-tidy/performance/PerformanceTidyModule.cpp b/clang-tools-extra/clang-tidy/performance/PerformanceTidyModule.cpp
index 9e0fa6f88b36a..6c45f8678fe63 100644
--- a/clang-tools-extra/clang-tidy/performance/PerformanceTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/performance/PerformanceTidyModule.cpp
@@ -17,6 +17,7 @@
 #include "InefficientAlgorithmCheck.h"
 #include "InefficientStringConcatenationCheck.h"
 #include "InefficientVectorOperationCheck.h"
+#include "LostStdMoveCheck.h"
 #include "MoveConstArgCheck.h"
 #include "MoveConstructorInitCheck.h"
 #include "NoAutomaticMoveCheck.h"
@@ -49,6 +50,7 @@ class PerformanceModule : public ClangTidyModule {
         "performance-inefficient-string-concatenation");
     CheckFactories.registerCheck<InefficientVectorOperationCheck>(
         "performance-inefficient-vector-operation");
+    CheckFactories.registerCheck<LostStdMoveCheck>("performance-lost-std-move");
     CheckFactories.registerCheck<MoveConstArgCheck>(
         "performance-move-const-arg");
     CheckFactories.registerCheck<MoveConstructorInitCheck>(
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 6d91748e4cef1..17da163ff041c 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -212,6 +212,11 @@ New checks
   Recommends the smallest possible underlying type for an ``enum`` or ``enum``
   class based on the range of its enumerators.
 
+- New :doc:`performance-lost-std-move
+  <clang-tidy/checks/performance/lost-std-move>` check.
+
+  Searches for lost std::move().
+
 - New :doc:`readability-reference-to-constructed-temporary
   <clang-tidy/checks/readability/reference-to-constructed-temporary>` check.
 
diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst b/clang-tools-extra/docs/clang-tidy/checks/list.rst
index 31f0e090db1d7..2eba4aacb2c33 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -321,6 +321,7 @@ Clang-Tidy Checks
    :doc:`performance-inefficient-algorithm <performance/inefficient-algorithm>`, "Yes"
    :doc:`performance-inefficient-string-concatenation <performance/inefficient-string-concatenation>`,
    :doc:`performance-inefficient-vector-operation <performance/inefficient-vector-operation>`, "Yes"
+   :doc:`performance-lost-std-move <performance/lost-std-move>`, "Yes"
    :doc:`performance-move-const-arg <performance/move-const-arg>`, "Yes"
    :doc:`performance-move-constructor-init <performance/move-constructor-init>`,
    :doc:`performance-no-automatic-move <performance/no-automatic-move>`,
diff --git a/clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst b/clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst
new file mode 100644
index 0000000000000..ded49de7b8126
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst
@@ -0,0 +1,14 @@
+.. title:: clang-tidy - performance-lost-std-move
+
+performance-lost-std-move
+=========================
+
+The check warns if copy constructor is used instead of std::move().
+
+.. code-block:: c++
+
+   void f(X);
+
+   void g(X x) {
+     f(x);  // warning: Could be std::move() [performance-lost-std-move]
+   }
diff --git a/clang-tools-extra/test/clang-tidy/checkers/performance/lost-std-move.cpp b/clang-tools-extra/test/clang-tidy/checkers/performance/lost-std-move.cpp
new file mode 100644
index 0000000000000..ce2d1b972dbd5
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/performance/lost-std-move.cpp
@@ -0,0 +1,108 @@
+// RUN: %check_clang_tidy %s performance-lost-std-move %t
+
+namespace std {
+
+template<typename T>
+class shared_ptr {
+public:
+  T& operator*() { return reinterpret_cast<T&>(*this); }
+  shared_ptr() {}
+  shared_ptr(const shared_ptr<T>&) {}
+};
+
+template<typename T>
+T&& move(T&)
+{
+}
+
+} // namespace std
+
+int f(std::shared_ptr<int>);
+
+void f_arg(std::shared_ptr<int> ptr)
+{
+  if (*ptr)
+    f(ptr);
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: Could be std::move() [performance-lost-std-move]
+}
+
+void f_rvalue_ref(std::shared_ptr<int>&& ptr)
+{
+  if (*ptr)
+    f(ptr);
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: Could be std::move() [performance-lost-std-move]
+}
+
+using SharedPtr = std::shared_ptr<int>;
+void f_using(SharedPtr ptr)
+{
+  if (*ptr)
+    f(ptr);
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: Could be std::move() [performance-lost-std-move]
+}
+
+void f_local()
+{
+  std::shared_ptr<int> ptr;
+  if (*ptr)
+    f(ptr);
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: Could be std::move() [performance-lost-std-move]
+}
+
+void f_move()
+{
+  std::shared_ptr<int> ptr;
+  if (*ptr)
+    f(std::move(ptr));
+}
+
+void f_ref(std::shared_ptr<int> &ptr)
+{
+  if (*ptr)
+    f(ptr);
+}
+
+std::shared_ptr<int> f_return()
+{
+  std::shared_ptr<int> ptr;
+  return ptr;
+}
+
+void f_still_used(std::shared_ptr<int> ptr)
+{
+  if (*ptr)
+    f(ptr);
+
+  *ptr = 1;
+  *ptr = *ptr;
+}
+
+void f_cycle1()
+{
+  std::shared_ptr<int> ptr;
+  for(;;)
+    f(ptr);
+}
+
+void f_cycle2()
+{
+  std::shared_ptr<int> ptr;
+  for(int i=0; i<5; i++)
+    f(ptr);
+}
+
+void f_cycle3()
+{
+  std::shared_ptr<int> ptr;
+  while (*ptr) {
+    f(ptr);
+  }
+}
+
+void f_cycle4()
+{
+  std::shared_ptr<int> ptr;
+  do {
+    f(ptr);
+  } while (*ptr);
+}

llvmbot · 2025-05-12T10:09:10Z

@llvm/pr-subscribers-clang-tidy

Author: Vasiliy Kulikov (segoon)

Changes

Full diff: https://github.com/llvm/llvm-project/pull/139525.diff

8 Files Affected:

(modified) clang-tools-extra/clang-tidy/performance/CMakeLists.txt (+1)
(added) clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp (+96)
(added) clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.h (+37)
(modified) clang-tools-extra/clang-tidy/performance/PerformanceTidyModule.cpp (+2)
(modified) clang-tools-extra/docs/ReleaseNotes.rst (+5)
(modified) clang-tools-extra/docs/clang-tidy/checks/list.rst (+1)
(added) clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst (+14)
(added) clang-tools-extra/test/clang-tidy/checkers/performance/lost-std-move.cpp (+108)

diff --git a/clang-tools-extra/clang-tidy/performance/CMakeLists.txt b/clang-tools-extra/clang-tidy/performance/CMakeLists.txt
index 81128ff086021..333abd10a583a 100644
--- a/clang-tools-extra/clang-tidy/performance/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/performance/CMakeLists.txt
@@ -12,6 +12,7 @@ add_clang_library(clangTidyPerformanceModule
   InefficientAlgorithmCheck.cpp
   InefficientStringConcatenationCheck.cpp
   InefficientVectorOperationCheck.cpp
+  LostStdMoveCheck.cpp
   MoveConstArgCheck.cpp
   MoveConstructorInitCheck.cpp
   NoAutomaticMoveCheck.cpp
diff --git a/clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp b/clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp
new file mode 100644
index 0000000000000..26148e1d26de9
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp
@@ -0,0 +1,96 @@
+//===--- LostStdMoveCheck.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 "LostStdMoveCheck.h"
+#include "../utils/DeclRefExprUtils.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::performance {
+
+using utils::decl_ref_expr::allDeclRefExprs;
+
+AST_MATCHER(CXXRecordDecl, hasTrivialMoveConstructor) {
+  return Node.hasDefinition() && Node.hasTrivialMoveConstructor();
+}
+
+void LostStdMoveCheck::registerMatchers(MatchFinder *Finder) {
+  auto returnParent =
+      hasParent(expr(hasParent(cxxConstructExpr(hasParent(returnStmt())))));
+
+  Finder->addMatcher(
+      declRefExpr(
+          // not "return x;"
+          unless(returnParent),
+
+          unless(hasType(namedDecl(hasName("::std::string_view")))),
+
+          // non-trivial type
+          hasType(hasCanonicalType(hasDeclaration(cxxRecordDecl()))),
+
+          // non-trivial X(X&&)
+          unless(hasType(hasCanonicalType(
+              hasDeclaration(cxxRecordDecl(hasTrivialMoveConstructor()))))),
+
+          // Not in a cycle
+          unless(hasAncestor(forStmt())), unless(hasAncestor(doStmt())),
+          unless(hasAncestor(whileStmt())),
+
+          // only non-X&
+          unless(hasDeclaration(
+              varDecl(hasType(qualType(lValueReferenceType()))))),
+
+          hasDeclaration(
+              varDecl(hasAncestor(functionDecl().bind("func"))).bind("decl")),
+
+          hasParent(expr(hasParent(cxxConstructExpr())).bind("use_parent")))
+          .bind("use"),
+      this);
+}
+
+const Expr *LostStdMoveCheck::getLastVarUsage(const VarDecl &Var,
+                                              const Decl &Func,
+                                              ASTContext &Context) {
+  auto Exprs = allDeclRefExprs(Var, Func, Context);
+
+  const Expr *LastExpr = nullptr;
+  for (const auto &Expr : Exprs) {
+    if (!LastExpr)
+      LastExpr = Expr;
+
+    if (LastExpr->getBeginLoc() < Expr->getBeginLoc())
+      LastExpr = Expr;
+  }
+
+  return LastExpr;
+}
+
+void LostStdMoveCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *MatchedDecl = Result.Nodes.getNodeAs<VarDecl>("decl");
+  const auto *MatchedFunc = Result.Nodes.getNodeAs<FunctionDecl>("func");
+  const auto *MatchedUse = Result.Nodes.getNodeAs<Expr>("use");
+  const auto *MatchedUseCall = Result.Nodes.getNodeAs<CallExpr>("use_parent");
+
+  if (MatchedUseCall)
+    return;
+
+  const auto *LastUsage =
+      getLastVarUsage(*MatchedDecl, *MatchedFunc, *Result.Context);
+  if (LastUsage == nullptr)
+    return;
+
+  if (LastUsage->getBeginLoc() > MatchedUse->getBeginLoc()) {
+    // "use" is not the last reference to x
+    return;
+  }
+
+  diag(LastUsage->getBeginLoc(), "Could be std::move()");
+}
+
+} // namespace clang::tidy::performance
diff --git a/clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.h b/clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.h
new file mode 100644
index 0000000000000..c62c3f6448a82
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.h
@@ -0,0 +1,37 @@
+//===--- LostStdMoveCheck.h - clang-tidy ------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PERFORMANCE_LOSTSTDMOVECHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PERFORMANCE_LOSTSTDMOVECHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang::tidy::performance {
+
+/// Search for lost std::move().
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/performance/lost-std-move.html
+class LostStdMoveCheck : public ClangTidyCheck {
+public:
+  LostStdMoveCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.CPlusPlus;
+  }
+
+private:
+  const Expr *getLastVarUsage(const VarDecl &Var, const Decl &Func,
+                              ASTContext &Context);
+};
+
+} // namespace clang::tidy::performance
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PERFORMANCE_LOSTSTDMOVECHECK_H
diff --git a/clang-tools-extra/clang-tidy/performance/PerformanceTidyModule.cpp b/clang-tools-extra/clang-tidy/performance/PerformanceTidyModule.cpp
index 9e0fa6f88b36a..6c45f8678fe63 100644
--- a/clang-tools-extra/clang-tidy/performance/PerformanceTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/performance/PerformanceTidyModule.cpp
@@ -17,6 +17,7 @@
 #include "InefficientAlgorithmCheck.h"
 #include "InefficientStringConcatenationCheck.h"
 #include "InefficientVectorOperationCheck.h"
+#include "LostStdMoveCheck.h"
 #include "MoveConstArgCheck.h"
 #include "MoveConstructorInitCheck.h"
 #include "NoAutomaticMoveCheck.h"
@@ -49,6 +50,7 @@ class PerformanceModule : public ClangTidyModule {
         "performance-inefficient-string-concatenation");
     CheckFactories.registerCheck<InefficientVectorOperationCheck>(
         "performance-inefficient-vector-operation");
+    CheckFactories.registerCheck<LostStdMoveCheck>("performance-lost-std-move");
     CheckFactories.registerCheck<MoveConstArgCheck>(
         "performance-move-const-arg");
     CheckFactories.registerCheck<MoveConstructorInitCheck>(
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 6d91748e4cef1..17da163ff041c 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -212,6 +212,11 @@ New checks
   Recommends the smallest possible underlying type for an ``enum`` or ``enum``
   class based on the range of its enumerators.
 
+- New :doc:`performance-lost-std-move
+  <clang-tidy/checks/performance/lost-std-move>` check.
+
+  Searches for lost std::move().
+
 - New :doc:`readability-reference-to-constructed-temporary
   <clang-tidy/checks/readability/reference-to-constructed-temporary>` check.
 
diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst b/clang-tools-extra/docs/clang-tidy/checks/list.rst
index 31f0e090db1d7..2eba4aacb2c33 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -321,6 +321,7 @@ Clang-Tidy Checks
    :doc:`performance-inefficient-algorithm <performance/inefficient-algorithm>`, "Yes"
    :doc:`performance-inefficient-string-concatenation <performance/inefficient-string-concatenation>`,
    :doc:`performance-inefficient-vector-operation <performance/inefficient-vector-operation>`, "Yes"
+   :doc:`performance-lost-std-move <performance/lost-std-move>`, "Yes"
    :doc:`performance-move-const-arg <performance/move-const-arg>`, "Yes"
    :doc:`performance-move-constructor-init <performance/move-constructor-init>`,
    :doc:`performance-no-automatic-move <performance/no-automatic-move>`,
diff --git a/clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst b/clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst
new file mode 100644
index 0000000000000..ded49de7b8126
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst
@@ -0,0 +1,14 @@
+.. title:: clang-tidy - performance-lost-std-move
+
+performance-lost-std-move
+=========================
+
+The check warns if copy constructor is used instead of std::move().
+
+.. code-block:: c++
+
+   void f(X);
+
+   void g(X x) {
+     f(x);  // warning: Could be std::move() [performance-lost-std-move]
+   }
diff --git a/clang-tools-extra/test/clang-tidy/checkers/performance/lost-std-move.cpp b/clang-tools-extra/test/clang-tidy/checkers/performance/lost-std-move.cpp
new file mode 100644
index 0000000000000..ce2d1b972dbd5
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/performance/lost-std-move.cpp
@@ -0,0 +1,108 @@
+// RUN: %check_clang_tidy %s performance-lost-std-move %t
+
+namespace std {
+
+template<typename T>
+class shared_ptr {
+public:
+  T& operator*() { return reinterpret_cast<T&>(*this); }
+  shared_ptr() {}
+  shared_ptr(const shared_ptr<T>&) {}
+};
+
+template<typename T>
+T&& move(T&)
+{
+}
+
+} // namespace std
+
+int f(std::shared_ptr<int>);
+
+void f_arg(std::shared_ptr<int> ptr)
+{
+  if (*ptr)
+    f(ptr);
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: Could be std::move() [performance-lost-std-move]
+}
+
+void f_rvalue_ref(std::shared_ptr<int>&& ptr)
+{
+  if (*ptr)
+    f(ptr);
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: Could be std::move() [performance-lost-std-move]
+}
+
+using SharedPtr = std::shared_ptr<int>;
+void f_using(SharedPtr ptr)
+{
+  if (*ptr)
+    f(ptr);
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: Could be std::move() [performance-lost-std-move]
+}
+
+void f_local()
+{
+  std::shared_ptr<int> ptr;
+  if (*ptr)
+    f(ptr);
+  // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: Could be std::move() [performance-lost-std-move]
+}
+
+void f_move()
+{
+  std::shared_ptr<int> ptr;
+  if (*ptr)
+    f(std::move(ptr));
+}
+
+void f_ref(std::shared_ptr<int> &ptr)
+{
+  if (*ptr)
+    f(ptr);
+}
+
+std::shared_ptr<int> f_return()
+{
+  std::shared_ptr<int> ptr;
+  return ptr;
+}
+
+void f_still_used(std::shared_ptr<int> ptr)
+{
+  if (*ptr)
+    f(ptr);
+
+  *ptr = 1;
+  *ptr = *ptr;
+}
+
+void f_cycle1()
+{
+  std::shared_ptr<int> ptr;
+  for(;;)
+    f(ptr);
+}
+
+void f_cycle2()
+{
+  std::shared_ptr<int> ptr;
+  for(int i=0; i<5; i++)
+    f(ptr);
+}
+
+void f_cycle3()
+{
+  std::shared_ptr<int> ptr;
+  while (*ptr) {
+    f(ptr);
+  }
+}
+
+void f_cycle4()
+{
+  std::shared_ptr<int> ptr;
+  do {
+    f(ptr);
+  } while (*ptr);
+}

firewave · 2025-05-12T10:34:46Z

See also #53489 and #57908.

CC @Febbe

github-actions · 2025-05-12T12:23:12Z

✅ With the latest revision this PR passed the C/C++ code formatter.

EugeneZelenko · 2025-05-12T14:18:42Z

clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp

+const Expr *LostStdMoveCheck::getLastVarUsage(const VarDecl &Var,
+                                              const Decl &Func,
+                                              ASTContext &Context) {
+  auto Exprs = allDeclRefExprs(Var, Func, Context);


Please do not use auto unless type is explicitly states in same statement or iterator.

EugeneZelenko · 2025-05-12T14:19:04Z

clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp

+  if (MatchedUseCall)
+    return;
+
+  const auto *LastUsage =


EugeneZelenko · 2025-05-12T14:19:38Z

clang-tools-extra/docs/ReleaseNotes.rst

+- New :doc:`performance-lost-std-move
+  <clang-tidy/checks/performance/lost-std-move>` check.
+
+  Searches for lost std::move().


Suggested change

Searches for lost std::move().

Searches for lost ``std::move()``.

EugeneZelenko · 2025-05-12T14:20:01Z

clang-tools-extra/docs/ReleaseNotes.rst

 - New :doc:`readability-ambiguous-smartptr-reset-call
  <clang-tidy/checks/readability/ambiguous-smartptr-reset-call>` check.

+


Unintended change?

EugeneZelenko · 2025-05-12T14:20:47Z

clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst

+performance-lost-std-move
+=========================
+
+The check warns if copy constructor is used instead of std::move().


Please synchronize with statement in Release Notes. This check should be omitted.

vbvictor

Commented general suggestions/improvements for the check without deep dive into matchers/tests.

Please look at tests in previous attempt in creating such check https://reviews.llvm.org/D137205.
Check that all test cases from that PR are covered in your tests.
If some cases are not covered and you can't address them, please add them to Limitations in docs and leave a fixme.

vbvictor · 2025-05-21T15:05:05Z

clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.h

+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.CPlusPlus;


Suggested change

return LangOpts.CPlusPlus;

return LangOpts.CPlusPlus11;

vbvictor · 2025-05-21T15:06:27Z

clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.h

+  }
+
+private:
+  const Expr *getLastVarUsage(const VarDecl &Var, const Decl &Func,


this should be converted to static function and move to .cpp file if no fields of check class are needed

vbvictor · 2025-05-21T15:07:45Z

clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp

+  llvm::SmallPtrSet<const DeclRefExpr *, 16> Exprs = allDeclRefExprs(Var, Func, Context);
+
+  const Expr *LastExpr = nullptr;
+  for (const auto &Expr : Exprs) {


Use explicit type instead of auto if it isn't written explicitly in code line.

vbvictor · 2025-05-21T15:07:51Z

clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp

+template <typename Node>
+void extractNodesByIdTo(ArrayRef<BoundNodes> Matches, StringRef ID,
+                        llvm::SmallPtrSet<const Node *, 16> &Nodes) {
+  for (const auto &Match : Matches)


vbvictor · 2025-05-21T15:10:00Z

clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp

+
+  // Calculate X usage count in the statement
+  llvm::SmallPtrSet<const DeclRefExpr *, 16> DeclRefs;
+  auto Matches = match(


vbvictor · 2025-05-21T15:13:10Z

clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp

+    return;
+  }
+
+  diag(LastUsage->getBeginLoc(), "Could be std::move()");


Try to provide fixits with the insertion of std::move

vbvictor · 2025-05-21T15:13:38Z

clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.h

+
+namespace clang::tidy::performance {
+
+/// Search for lost std::move().


This should be synced with release notes and check docs

vbvictor · 2025-05-21T15:19:15Z

clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst

+performance-lost-std-move
+=========================
+
+Warns if copy constructor is used instead of ``std::move()``.


This need a little more description when the check will warn, e.g when this will fire, with what types?
Look for reference at https://reviews.llvm.org/D137205

vbvictor · 2025-05-21T15:20:55Z

clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst

+performance-lost-std-move
+=========================
+
+Warns if copy constructor is used instead of ``std::move()``.


Nit suggestion: try make the description similar to already existing new checks in ReleaseNotes.rst.
Description should start with "Finds ..."

vbvictor · 2025-05-21T15:21:47Z

clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst

+
+   void g(X x) {
+     f(x);  // warning: Could be std::move() [performance-lost-std-move]
+   }


Give examples when check will not warn

EugeneZelenko · 2025-06-01T05:03:45Z

clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp

+  const auto* MatchedLeafStatement =
+      Result.Nodes.getNodeAs<Stmt>("leaf_statement");
+
+  if (!MatchedDecl->hasLocalStorage()) return;


Should be two lines as next statement.

EugeneZelenko · 2025-06-01T05:04:16Z

clang-tools-extra/docs/ReleaseNotes.rst

@@ -145,8 +145,75 @@ New checks
 - New :doc:`readability-ambiguous-smartptr-reset-call
  <clang-tidy/checks/readability/ambiguous-smartptr-reset-call>` check.

+<<<<<<< HEAD


Rebase artifact.

EugeneZelenko · 2025-06-01T14:44:59Z

clang-tools-extra/clang-tidy/performance/LostStdMoveCheck.cpp

+  auto Matches = match(
+      decl(forEachDescendant(
+          declRefExpr(to(varDecl(equalsNode(&VarDecl))),
+


Excessive newline. Same in other places.

EugeneZelenko · 2025-06-01T14:47:22Z

clang-tools-extra/docs/ReleaseNotes.rst

+- New :doc:`performance-lost-std-move
+  <clang-tidy/checks/performance/lost-std-move>` check.
+
+  Warns if copy constructor is used instead of std::move() and suggests a fix.


Suggested change

Warns if copy constructor is used instead of std::move() and suggests a fix.

Warns if copy constructor is used instead of ``std::move()`` and suggests a fix.

EugeneZelenko · 2025-06-01T14:47:40Z

clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst

+performance-lost-std-move
+=========================
+
+Warns if copy constructor is used instead of std::move() and suggests a fix.


Suggested change

Warns if copy constructor is used instead of std::move() and suggests a fix.

Warns if copy constructor is used instead of ``std::move()`` and suggests a fix.

EugeneZelenko · 2025-06-01T14:48:03Z

clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst

+   }
+
+It finds the last local variable usage, and if it is a copy, emits a warning.
+The check is based on pure AST matching and doesn't take into account any data flow information.


Please follow 80-characters limit.

EugeneZelenko · 2025-06-01T14:48:58Z

clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst

+     y.f();  // ...but it is still used
+   }
+
+Such rare cases should be silenced using `// NOLINT`.


Should general functionality be mentioned?

vbvictor · 2025-06-01T15:20:44Z

clang-tools-extra/docs/clang-tidy/checks/performance/lost-std-move.rst

+Thus, it doesn't catch assign-after-copy cases.
+Also it doesn't notice variable references "behind the scenes":
+
+.. code-block:: c++
+
+   void f(X);
+
+   void g(X x) {
+     auto &y = x;
+     f(x);  // emits a warning...
+     y.f();  // ...but it is still used
+   }


I strongly oppose this design decision. In this check we should minimize the number of false-positives (and not leave any known false-positives). It's better to have false-negatives than false-positives, so an easy solution to this case could be:
If the variable is binded to a reference then we can not emit a warning.

The problem is that any binding to a reference should skip the check. E.g.

void f(X); void g(X&); void func(X x) { g(x); // reference is created, we may not move from x anymore f(x); // no fix }

I'm afraid too many cases are skipped due to this problem.

We can distinguish cases where a variable was an initializer to VarDecl of type X& and where the variable was used as a function parameter as DeclRefExpr, https://godbolt.org/z/brKdcsn61.
Even if this can't be fixed, I think it's better to skip cases than have false-positives for this check.

In your 3-liner example, it may be easy to spot a false-positive, but if void g(X x) is 100+ lines long it will be hard to verify correctness. Thought clang-static-analyzer may find these cases, not everyone use it.

May other reviews share their opinions on this matter.

The problem is that any binding to a reference should skip the check. E.g.

void f(X); void g(X&); void func(X x) { g(x); // reference is created, we may not move from x anymore f(x); // no fix }

I'm afraid too many cases are skipped due to this problem.

Would it be a compromise to enable this via an option that is disabled by default?
Also, disable automatic fixes for those cases, so every change has to be done on purpose?

[clang-tidy] Add check performance-lost-std-move

3abbce9

llvmbot added clang-tools-extra clang-tidy labels May 12, 2025

segoon added 2 commits May 12, 2025 15:13

f(x, x)

4a1a77b

test

f74066d

EugeneZelenko requested review from PiotrZSL, HerrCai0907 and carlosgalvezp May 12, 2025 14:17

EugeneZelenko reviewed May 12, 2025

View reviewed changes

vbvictor reviewed May 21, 2025

View reviewed changes

segoon added 9 commits May 26, 2025 12:37

review fixes

edd4800

auto -> Expr

5359c69

FixIt

5bb6af6

f((x))

592d79b

w

1710c2f

Merge remote-tracking branch 'origin/main' into feature/lost-std-move

b4824ef

thread_local, extern, static

60e4aca

better test

a27b1b3

fixes

6aacd41

segoon force-pushed the feature/lost-std-move branch from d3b8c17 to 6aacd41 Compare June 1, 2025 04:53

segoon added 2 commits June 1, 2025 08:02

[=] test

71cd708

fix

402ba55

EugeneZelenko reviewed Jun 1, 2025

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segoon added 3 commits June 1, 2025 08:14

docs

fdf01b6

format

24357a2

format

b48425b

Merge remote-tracking branch 'origin/main' into feature/lost-std-move

986d6aa

EugeneZelenko reviewed Jun 1, 2025

View reviewed changes

vbvictor reviewed Jun 1, 2025

View reviewed changes

	Searches for lost std::move().
	Searches for lost ``std::move()``.

		- New :doc:`readability-ambiguous-smartptr-reset-call
		<clang-tidy/checks/readability/ambiguous-smartptr-reset-call>` check.


		namespace clang::tidy::performance {

		/// Search for lost std::move().

	Warns if copy constructor is used instead of std::move() and suggests a fix.
	Warns if copy constructor is used instead of ``std::move()`` and suggests a fix.

[clang-tidy] Add check performance-lost-std-move #139525

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[clang-tidy] Add check performance-lost-std-move #139525

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