Merge lifetimebound attribute on implicit 'this' across method redeclarations

Author: usx95

clang/include/clang/Analysis/Analyses/LifetimeSafety/LifetimeAnnotations.h

@@ -10,6 +10,7 @@
 #ifndef LLVM_CLANG_ANALYSIS_ANALYSES_LIFETIMEANNOTATIONS_H
 #define LLVM_CLANG_ANALYSIS_ANALYSES_LIFETIMEANNOTATIONS_H
 
+#include "clang/AST/Attr.h"
 #include "clang/AST/DeclCXX.h"
 
 namespace clang ::lifetimes {

clang/lib/Analysis/LifetimeSafety/LifetimeAnnotations.cpp

@@ -52,22 +52,33 @@ bool isAssignmentOperatorLifetimeBound(const CXXMethodDecl *CMD) {
          CMD->getParamDecl(0)->hasAttr<clang::LifetimeBoundAttr>();
 }
 
+/// Check if a function has a lifetimebound attribute on its function type
+/// (which represents the implicit 'this' parameter for methods).
+/// Returns the attribute if found, nullptr otherwise.
+static const LifetimeBoundAttr *
+getLifetimeBoundAttrFromFunctionType(const TypeSourceInfo &TSI) {
+  // Walk through the type layers looking for a lifetimebound attribute.
+  TypeLoc TL = TSI.getTypeLoc();
+  while (true) {
+    auto ATL = TL.getAsAdjusted<AttributedTypeLoc>();
+    if (!ATL)
+      break;
+    if (auto *LBAttr = ATL.getAttrAs<LifetimeBoundAttr>())
+      return LBAttr;
+    TL = ATL.getModifiedLoc();
+  }
+  return nullptr;
+}
+
 bool implicitObjectParamIsLifetimeBound(const FunctionDecl *FD) {
   FD = getDeclWithMergedLifetimeBoundAttrs(FD);
-  const TypeSourceInfo *TSI = FD->getTypeSourceInfo();
-  if (!TSI)
-    return false;
-  // Don't declare this variable in the second operand of the for-statement;
-  // GCC miscompiles that by ending its lifetime before evaluating the
-  // third operand. See gcc.gnu.org/PR86769.
-  AttributedTypeLoc ATL;
-  for (TypeLoc TL = TSI->getTypeLoc();
-       (ATL = TL.getAsAdjusted<AttributedTypeLoc>());
-       TL = ATL.getModifiedLoc()) {
-    if (ATL.getAttrAs<clang::LifetimeBoundAttr>())
+  // Attribute merging doesn't work well with attributes on function types (like
+  // 'this' param). We need to check all redeclarations.
+  for (const FunctionDecl *Redecl : FD->redecls()) {
+    const TypeSourceInfo *TSI = Redecl->getTypeSourceInfo();
+    if (TSI && getLifetimeBoundAttrFromFunctionType(*TSI))
       return true;
   }
-
   return isNormalAssignmentOperator(FD);
 }
 

clang/test/Sema/warn-lifetime-analysis-nocfg.cpp

@@ -1039,3 +1039,141 @@ const char* foo() {
 }
 
 } // namespace GH127195
+
+// Lifetimebound on definition vs declaration on implicit this param.
+namespace GH175391 {
+// Version A: Attribute on declaration only
+class StringA {
+public:
+    const char* data() const [[clang::lifetimebound]];  // Declaration with attribute
+private:
+    char buffer[32] = "hello";
+};
+inline const char* StringA::data() const {  // Definition WITHOUT attribute
+    return buffer;
+}
+
+// Version B: Attribute on definition only
+class StringB {
+public:
+    const char* data() const;  // No attribute
+private:
+    char buffer[32] = "hello";
+};
+inline const char* StringB::data() const [[clang::lifetimebound]] {
+    return buffer;
+}
+
+// Version C: Attribute on BOTH declaration and definition
+class StringC {
+public:
+    const char* data() const [[clang::lifetimebound]];
+private:
+    char buffer[32] = "hello";
+};
+inline const char* StringC::data() const [[clang::lifetimebound]] {
+    return buffer;
+}
+
+// TEMPLATED VERSIONS
+
+// Template Version A: Attribute on declaration only
+template<typename T>
+class StringTemplateA {
+public:
+    const T* data() const [[clang::lifetimebound]];  // Declaration with attribute
+private:
+    T buffer[32];
+};
+template<typename T>
+inline const T* StringTemplateA<T>::data() const {  // Definition WITHOUT attribute
+    return buffer;
+}
+
+// Template Version B: Attribute on definition only
+template<typename T>
+class StringTemplateB {
+public:
+    const T* data() const;  // No attribute
+private:
+    T buffer[32];
+};
+template<typename T>
+inline const T* StringTemplateB<T>::data() const [[clang::lifetimebound]] {
+    return buffer;
+}
+
+// Template Version C: Attribute on BOTH declaration and definition
+template<typename T>
+class StringTemplateC {
+public:
+    const T* data() const [[clang::lifetimebound]];
+private:
+    T buffer[32];
+};
+template<typename T>
+inline const T* StringTemplateC<T>::data() const [[clang::lifetimebound]] {
+    return buffer;
+}
+
+// TEMPLATE SPECIALIZATION VERSIONS
+
+// Template predeclarations for specializations
+template<typename T> class StringTemplateSpecA;
+template<typename T> class StringTemplateSpecB;
+template<typename T> class StringTemplateSpecC;
+
+// Template Specialization Version A: Attribute on declaration only - <char> specialization
+template<>
+class StringTemplateSpecA<char> {
+public:
+    const char* data() const [[clang::lifetimebound]];  // Declaration with attribute
+private:
+    char buffer[32] = "hello";
+};
+inline const char* StringTemplateSpecA<char>::data() const {  // Definition WITHOUT attribute
+    return buffer;
+}
+
+// Template Specialization Version B: Attribute on definition only - <char> specialization
+template<>
+class StringTemplateSpecB<char> {
+public:
+    const char* data() const;  // No attribute
+private:
+    char buffer[32] = "hello";
+};
+inline const char* StringTemplateSpecB<char>::data() const [[clang::lifetimebound]] {
+    return buffer;
+}
+
+// Template Specialization Version C: Attribute on BOTH declaration and definition - <char> specialization
+template<>
+class StringTemplateSpecC<char> {
+public:
+    const char* data() const [[clang::lifetimebound]];
+private:
+    char buffer[32] = "hello";
+};
+inline const char* StringTemplateSpecC<char>::data() const [[clang::lifetimebound]] {
+    return buffer;
+}
+
+void test() {
+    // Non-templated tests
+    const auto ptrA = StringA().data();  // Declaration-only attribute  // expected-warning {{temporary whose address is used}}
+    const auto ptrB = StringB().data();  // Definition-only attribute   // expected-warning {{temporary whose address is used}}
+    const auto ptrC = StringC().data();  // Both have attribute         // expected-warning {{temporary whose address is used}}
+
+    // Templated tests (generic templates)
+    const auto ptrTA = StringTemplateA<char>().data();  // Declaration-only attribute // expected-warning {{temporary whose address is used}}
+    // FIXME: Definition is not instantiated until the end of TU. The attribute is not merged when this call is processed.
+    const auto ptrTB = StringTemplateB<char>().data();  // Definition-only attribute
+    const auto ptrTC = StringTemplateC<char>().data();  // Both have attribute        // expected-warning {{temporary whose address is used}}
+
+    // Template specialization tests
+    const auto ptrTSA = StringTemplateSpecA<char>().data();  // Declaration-only attribute  // expected-warning {{temporary whose address is used}}
+    const auto ptrTSB = StringTemplateSpecB<char>().data();  // Definition-only attribute   // expected-warning {{temporary whose address is used}}
+    const auto ptrTSC = StringTemplateSpecC<char>().data();  // Both have attribute         // expected-warning {{temporary whose address is used}}
+}
+} // namespace GH175391

clang/test/Sema/warn-lifetime-safety.cpp

@@ -1431,3 +1431,25 @@ void not_silenced_via_conditional(bool cond) {
   (void)v;  // expected-note 2 {{later used here}}
 }
 } // namespace do_not_warn_on_std_move
+
+// Implicit this annotations with redecls.
+namespace GH172013 {
+// https://github.com/llvm/llvm-project/issues/62072
+// https://github.com/llvm/llvm-project/issues/172013
+struct S {
+    View x() const [[clang::lifetimebound]];
+    MyObj i;
+};
+
+View S::x() const { return i; }
+
+void bar() {
+    View x;
+    {
+        S s;
+        x = s.x(); // expected-warning {{object whose reference is captured does not live long enough}}
+        View y = S().x(); // FIXME: Handle temporaries.
+    } // expected-note {{destroyed here}}
+    (void)x; // expected-note {{used here}}
+}
+}

clang/test/SemaCXX/attr-lifetimebound.cpp

@@ -75,6 +75,27 @@ namespace usage_ok {
     r = A(1); // expected-warning {{object backing the pointer 'r' will be destroyed at the end of the full-expression}}
   }
 
+  // Test that lifetimebound on implicit 'this' is propagated across redeclarations
+  struct B {
+    int *method() [[clang::lifetimebound]];
+    int i;
+  };
+  int *B::method() { return &i; }
+
+  // Test that lifetimebound on implicit 'this' is propagated across redeclarations
+  struct C {
+    int *method();
+    int i;
+  };
+  int *C::method() [[clang::lifetimebound]] { return &i; }
+
+  void test_lifetimebound_on_implicit_this() {
+    int *t = B().method();  // expected-warning {{temporary whose address is used as value of local variable 't' will be destroyed at the end of the full-expression}}
+    t = {B().method()};     // expected-warning {{object backing the pointer 't' will be destroyed at the end of the full-expression}}
+    t = C().method();       // expected-warning {{object backing the pointer 't' will be destroyed at the end of the full-expression}}
+    t = {C().method()};     // expected-warning {{object backing the pointer 't' will be destroyed at the end of the full-expression}}
+  }
+
   struct FieldCheck {
     struct Set {
       int a;