Address comments

Author: hokein

clang/lib/Sema/CheckExprLifetime.cpp

@@ -535,9 +535,6 @@ static void visitFunctionCallArguments(IndirectLocalPath &Path, Expr *Call,
 
   bool EnableGSLAnalysis = !Callee->getASTContext().getDiagnostics().isIgnored(
       diag::warn_dangling_lifetime_pointer, SourceLocation());
-  bool EnableDanglingCapture =
-      !Callee->getASTContext().getDiagnostics().isIgnored(
-          diag::warn_dangling_reference_captured, SourceLocation());
   Expr *ObjectArg = nullptr;
   if (isa<CXXOperatorCallExpr>(Call) && Callee->isCXXInstanceMember()) {
     ObjectArg = Args[0];
@@ -628,11 +625,23 @@ static void visitFunctionCallArguments(IndirectLocalPath &Path, Expr *Call,
       VisitLifetimeBoundArg(Callee->getParamDecl(I), Arg);
     else if (const auto *CaptureAttr =
                  Callee->getParamDecl(I)->getAttr<LifetimeCaptureByAttr>();
-             EnableDanglingCapture && CaptureAttr &&
-             isa<CXXConstructorDecl>(Callee) &&
+             CaptureAttr && isa<CXXConstructorDecl>(Callee) &&
              llvm::any_of(CaptureAttr->params(), [](int ArgIdx) {
                return ArgIdx == LifetimeCaptureByAttr::THIS;
              }))
+      // `lifetime_capture_by(this)` in a class constructor has the same
+      // semantics as `lifetimebound`:
+      //
+      // struct Foo {
+      //   const int& a;
+      //   // Equivalent to Foo(const int& t [[clang::lifetimebound]])
+      //   Foo(const int& t [[clang::lifetime_capture_by(this)]]) : a(t) {}
+      // };
+      //
+      // In the implementation, `lifetime_capture_by` is treated as an alias for
+      // `lifetimebound` and shares the same code path. This implies the emitted
+      // diagnostics will be emitted under `-Wdangling`, not
+      // `-Wdangling-capture`.
       VisitLifetimeBoundArg(Callee->getParamDecl(I), Arg);
     else if (EnableGSLAnalysis && I == 0) {
       // Perform GSL analysis for the first argument

clang/test/Sema/warn-lifetime-analysis-capture-by.cpp

@@ -419,12 +419,19 @@ struct T {
 struct T2 {
   T2(const int& t [[clang::lifetime_capture_by(x)]], int& x);
 };
+struct T3 {
+  T3(const T& t [[clang::lifetime_capture_by(this)]]);
+};
+
 int foo(const T& t);
+int bar(const T& t[[clang::lifetimebound]]);
 
 void test() {
   auto x = foo(T(1)); // OK. no diagnosic
   T(1); // OK. no diagnostic
   T t(1); // expected-warning {{temporary whose address is used}}
+  auto y = bar(T(1)); // expected-warning {{temporary whose address is used}}
+  T3 t3(T(1)); // expected-warning {{temporary whose address is used}}
 
   int a;
   T2(1, a); // expected-warning {{object whose reference is captured by}}