[clang] Fix lifetimebound for field access (PR #100197)

[Utkarsh Saxena via cfe-commits]

https://github.com/usx95 updated https://github.com/llvm/llvm-project/pull/100197

>From b76d65484c3195f27e8d01208ccc6e6f8ab55273 Mon Sep 17 00:00:00 2001
From: Utkarsh Saxena <usx at google.com>
Date: Tue, 23 Jul 2024 19:41:44 +0000
Subject: [PATCH 1/4] Fix lifetimebound for field access

---
 clang/lib/Sema/CheckExprLifetime.cpp      |  8 ++++++++
 clang/test/SemaCXX/attr-lifetimebound.cpp | 21 +++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/clang/lib/Sema/CheckExprLifetime.cpp b/clang/lib/Sema/CheckExprLifetime.cpp
index 5c8ef564f30aa..4d26a2e0f50c6 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "CheckExprLifetime.h"
+#include "clang/AST/Decl.h"
 #include "clang/AST/Expr.h"
 #include "clang/Basic/DiagnosticSema.h"
 #include "clang/Sema/Initialization.h"
@@ -548,6 +549,13 @@ static void visitLocalsRetainedByReferenceBinding(IndirectLocalPath &Path,
                                        EnableLifetimeWarnings);
   }
 
+  if (auto* M = dyn_cast<MemberExpr>(Init)) {
+    // Lifetime of a field is the lifetime of the base object.
+    if (isa<FieldDecl>(M->getMemberDecl()))
+      visitLocalsRetainedByInitializer(Path, M->getBase(), Visit, true,
+                                       EnableLifetimeWarnings);
+  }
+
   if (isa<CallExpr>(Init)) {
     if (EnableLifetimeWarnings)
       handleGslAnnotatedTypes(Path, Init, Visit);
diff --git a/clang/test/SemaCXX/attr-lifetimebound.cpp b/clang/test/SemaCXX/attr-lifetimebound.cpp
index 70bc545c07bd9..b43c43bb21699 100644
--- a/clang/test/SemaCXX/attr-lifetimebound.cpp
+++ b/clang/test/SemaCXX/attr-lifetimebound.cpp
@@ -47,6 +47,26 @@ namespace usage_ok {
     q = A(); // expected-warning {{object backing the pointer q will be destroyed at the end of the full-expression}}
     r = A(1); // expected-warning {{object backing the pointer r will be destroyed at the end of the full-expression}}
   }
+
+  struct FieldCheck {
+    struct Set {
+      int a;
+    };
+    struct Pair {
+      const int& a;
+      int b;
+      Set c;
+    };
+    Pair p;  
+    FieldCheck(const int a): p(a){}
+    Pair& getPairR() [[clang::lifetimebound]] { return p; }
+    Pair* getPairP() [[clang::lifetimebound]] { return &p; }
+  };
+  void test_field_access() {
+    const int& a = FieldCheck{0}.getPairR().a; // expected-warning {{temporary bound to local reference 'a' will be destroyed at the end of the full-expression}}
+    const int& b = FieldCheck{0}.getPairP()->b; // expected-warning {{temporary bound to local reference 'b' will be destroyed at the end of the full-expression}}
+    const int& c = FieldCheck{0}.getPairP()->c.a; // expected-warning {{temporary bound to local reference 'c' will be destroyed at the end of the full-expression}}
+  }
 }
 
 # 1 "<std>" 1 3
@@ -239,3 +259,4 @@ namespace move_forward_et_al_examples {
   S X;
   S *AddressOfOk = std::addressof(X);
 } // namespace move_forward_et_al_examples
+

>From 247f986b7a4b4743826a53e9317c4a65ebe289fe Mon Sep 17 00:00:00 2001
From: Utkarsh Saxena <usx at google.com>
Date: Tue, 23 Jul 2024 20:32:33 +0000
Subject: [PATCH 2/4] release notes

---
 clang/docs/ReleaseNotes.rst | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 7ac6ed934290d..fdad9202c0ea9 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -744,6 +744,8 @@ Improvements to Clang's diagnostics
 - Clang now diagnoses dangling assignments for pointer-like objects (annotated with `[[gsl::Pointer]]`) under `-Wdangling-assignment-gsl` (off by default)
   Fixes #GH63310.
 
+- Clang now diagnoses dangling references to fields of temporary objects. Fixes #GH81589.
+
 Improvements to Clang's time-trace
 ----------------------------------
 

>From 3825954a382d6bedd79f7ad332cd6937c74fe5fa Mon Sep 17 00:00:00 2001
From: Utkarsh Saxena <usx at google.com>
Date: Tue, 23 Jul 2024 20:33:18 +0000
Subject: [PATCH 3/4] format

---
 clang/lib/Sema/CheckExprLifetime.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/lib/Sema/CheckExprLifetime.cpp b/clang/lib/Sema/CheckExprLifetime.cpp
index 4d26a2e0f50c6..66b61fbbbeda7 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -549,7 +549,7 @@ static void visitLocalsRetainedByReferenceBinding(IndirectLocalPath &Path,
                                        EnableLifetimeWarnings);
   }
 
-  if (auto* M = dyn_cast<MemberExpr>(Init)) {
+  if (auto *M = dyn_cast<MemberExpr>(Init)) {
     // Lifetime of a field is the lifetime of the base object.
     if (isa<FieldDecl>(M->getMemberDecl()))
       visitLocalsRetainedByInitializer(Path, M->getBase(), Visit, true,

>From dcfd225abfa0bcbd6e00f3c30c7c490982974fee Mon Sep 17 00:00:00 2001
From: Utkarsh Saxena <usx at google.com>
Date: Wed, 24 Jul 2024 08:46:06 +0000
Subject: [PATCH 4/4] Lifetime of reference type field is unknown. skip it

---
 clang/lib/Sema/CheckExprLifetime.cpp      | 5 +++--
 clang/test/SemaCXX/attr-lifetimebound.cpp | 7 ++++---
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/clang/lib/Sema/CheckExprLifetime.cpp b/clang/lib/Sema/CheckExprLifetime.cpp
index 66b61fbbbeda7..112cf3d081822 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -550,8 +550,9 @@ static void visitLocalsRetainedByReferenceBinding(IndirectLocalPath &Path,
   }
 
   if (auto *M = dyn_cast<MemberExpr>(Init)) {
-    // Lifetime of a field is the lifetime of the base object.
-    if (isa<FieldDecl>(M->getMemberDecl()))
+    // Lifetime of a non-reference type field is same as base object.
+    if (auto *F = dyn_cast<FieldDecl>(M->getMemberDecl());
+        F && !F->getType()->isReferenceType())
       visitLocalsRetainedByInitializer(Path, M->getBase(), Visit, true,
                                        EnableLifetimeWarnings);
   }
diff --git a/clang/test/SemaCXX/attr-lifetimebound.cpp b/clang/test/SemaCXX/attr-lifetimebound.cpp
index b43c43bb21699..78c1cb91e17a2 100644
--- a/clang/test/SemaCXX/attr-lifetimebound.cpp
+++ b/clang/test/SemaCXX/attr-lifetimebound.cpp
@@ -63,9 +63,10 @@ namespace usage_ok {
     Pair* getPairP() [[clang::lifetimebound]] { return &p; }
   };
   void test_field_access() {
-    const int& a = FieldCheck{0}.getPairR().a; // expected-warning {{temporary bound to local reference 'a' will be destroyed at the end of the full-expression}}
-    const int& b = FieldCheck{0}.getPairP()->b; // expected-warning {{temporary bound to local reference 'b' will be destroyed at the end of the full-expression}}
-    const int& c = FieldCheck{0}.getPairP()->c.a; // expected-warning {{temporary bound to local reference 'c' will be destroyed at the end of the full-expression}}
+    int x = 0;
+    const int& a = FieldCheck{x}.getPairR().a;
+    const int& b = FieldCheck{x}.getPairP()->b; // expected-warning {{temporary bound to local reference 'b' will be destroyed at the end of the full-expression}}
+    const int& c = FieldCheck{x}.getPairP()->c.a; // expected-warning {{temporary bound to local reference 'c' will be destroyed at the end of the full-expression}}
   }
 }