Revert "[Clang][CWG1815] Support lifetime extension of temporary created by aggregate initialization using a default member initializer (#87933)"

This reverts commit 17daa20.

Multiple examples on the PR
#87933

show regressions, so reverting until they can be fixed in the followup.

Author: erichkeane

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -10037,6 +10037,12 @@ def warn_new_dangling_initializer_list : Warning<
   "the allocated initializer list}0 "
   "will be destroyed at the end of the full-expression">,
   InGroup<DanglingInitializerList>;
+def warn_unsupported_lifetime_extension : Warning<
+  "lifetime extension of "
+  "%select{temporary|backing array of initializer list}0 created "
+  "by aggregate initialization using a default member initializer "
+  "is not yet supported; lifetime of %select{temporary|backing array}0 "
+  "will end at the end of the full-expression">, InGroup<Dangling>;
 
 // For non-floating point, expressions of the form x == x or x != x
 // should result in a warning, since these always evaluate to a constant.

clang/lib/Sema/SemaExpr.cpp

@@ -5618,9 +5618,10 @@ ExprResult Sema::BuildCXXDefaultArgExpr(SourceLocation CallLoc,
         Res = Immediate.TransformInitializer(Param->getInit(),
                                              /*NotCopy=*/false);
       });
-      if (Res.isUsable())
-        Res = ConvertParamDefaultArgument(Param, Res.get(),
-                                          Res.get()->getBeginLoc());
+      if (Res.isInvalid())
+        return ExprError();
+      Res = ConvertParamDefaultArgument(Param, Res.get(),
+                                        Res.get()->getBeginLoc());
       if (Res.isInvalid())
         return ExprError();
       Init = Res.get();
@@ -5656,7 +5657,7 @@ ExprResult Sema::BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field) {
   Expr *Init = nullptr;
 
   bool NestedDefaultChecking = isCheckingDefaultArgumentOrInitializer();
-  bool InLifetimeExtendingContext = isInLifetimeExtendingContext();
+
   EnterExpressionEvaluationContext EvalContext(
       *this, ExpressionEvaluationContext::PotentiallyEvaluated, Field);
 
@@ -5691,35 +5692,19 @@ ExprResult Sema::BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field) {
   ImmediateCallVisitor V(getASTContext());
   if (!NestedDefaultChecking)
     V.TraverseDecl(Field);
-
-  // CWG1815
-  // Support lifetime extension of temporary created by aggregate
-  // initialization using a default member initializer. We should always rebuild
-  // the initializer if it contains any temporaries (if the initializer
-  // expression is an ExprWithCleanups). Then make sure the normal lifetime
-  // extension code recurses into the default initializer and does lifetime
-  // extension when warranted.
-  bool ContainsAnyTemporaries =
-      isa_and_present<ExprWithCleanups>(Field->getInClassInitializer());
-  if (V.HasImmediateCalls || InLifetimeExtendingContext ||
-      ContainsAnyTemporaries) {
+  if (V.HasImmediateCalls) {
     ExprEvalContexts.back().DelayedDefaultInitializationContext = {Loc, Field,
                                                                    CurContext};
     ExprEvalContexts.back().IsCurrentlyCheckingDefaultArgumentOrInitializer =
         NestedDefaultChecking;
-    // Pass down lifetime extending flag, and collect temporaries in
-    // CreateMaterializeTemporaryExpr when we rewrite the call argument.
-    keepInLifetimeExtendingContext();
+
     EnsureImmediateInvocationInDefaultArgs Immediate(*this);
     ExprResult Res;
-
-    // Rebuild CXXDefaultInitExpr might cause diagnostics.
-    SFINAETrap Trap(*this);
     runWithSufficientStackSpace(Loc, [&] {
       Res = Immediate.TransformInitializer(Field->getInClassInitializer(),
                                            /*CXXDirectInit=*/false);
     });
-    if (Res.isUsable())
+    if (!Res.isInvalid())
       Res = ConvertMemberDefaultInitExpression(Field, Res.get(), Loc);
     if (Res.isInvalid()) {
       Field->setInvalidDecl();

clang/lib/Sema/SemaInit.cpp

@@ -8066,6 +8066,11 @@ static void visitLocalsRetainedByInitializer(IndirectLocalPath &Path,
 enum PathLifetimeKind {
   /// Lifetime-extend along this path.
   Extend,
+  /// We should lifetime-extend, but we don't because (due to technical
+  /// limitations) we can't. This happens for default member initializers,
+  /// which we don't clone for every use, so we don't have a unique
+  /// MaterializeTemporaryExpr to update.
+  ShouldExtend,
   /// Do not lifetime extend along this path.
   NoExtend
 };
@@ -8077,7 +8082,7 @@ shouldLifetimeExtendThroughPath(const IndirectLocalPath &Path) {
   PathLifetimeKind Kind = PathLifetimeKind::Extend;
   for (auto Elem : Path) {
     if (Elem.Kind == IndirectLocalPathEntry::DefaultInit)
-      Kind = PathLifetimeKind::Extend;
+      Kind = PathLifetimeKind::ShouldExtend;
     else if (Elem.Kind != IndirectLocalPathEntry::LambdaCaptureInit)
       return PathLifetimeKind::NoExtend;
   }
@@ -8197,6 +8202,18 @@ void Sema::checkInitializerLifetime(const InitializedEntity &Entity,
                               ExtendingEntity->allocateManglingNumber());
         // Also visit the temporaries lifetime-extended by this initializer.
         return true;
+
+      case PathLifetimeKind::ShouldExtend:
+        // We're supposed to lifetime-extend the temporary along this path (per
+        // the resolution of DR1815), but we don't support that yet.
+        //
+        // FIXME: Properly handle this situation. Perhaps the easiest approach
+        // would be to clone the initializer expression on each use that would
+        // lifetime extend its temporaries.
+        Diag(DiagLoc, diag::warn_unsupported_lifetime_extension)
+            << RK << DiagRange;
+        break;
+
       case PathLifetimeKind::NoExtend:
         // If the path goes through the initialization of a variable or field,
         // it can't possibly reach a temporary created in this full-expression.

clang/test/AST/ast-dump-default-init-json.cpp

@@ -789,10 +789,10 @@ void test() {
 // CHECK-NEXT:                  "valueCategory": "lvalue",
 // CHECK-NEXT:                  "extendingDecl": {
 // CHECK-NEXT:                   "id": "0x{{.*}}",
-// CHECK-NEXT:                   "kind": "VarDecl",
-// CHECK-NEXT:                   "name": "b",
+// CHECK-NEXT:                   "kind": "FieldDecl",
+// CHECK-NEXT:                   "name": "a",
 // CHECK-NEXT:                   "type": {
-// CHECK-NEXT:                    "qualType": "B"
+// CHECK-NEXT:                    "qualType": "const A &"
 // CHECK-NEXT:                   }
 // CHECK-NEXT:                  },
 // CHECK-NEXT:                  "storageDuration": "automatic",

clang/test/AST/ast-dump-default-init.cpp

@@ -13,7 +13,7 @@ void test() {
 }
 // CHECK: -CXXDefaultInitExpr 0x{{[^ ]*}} <{{.*}}> 'const A' lvalue has rewritten init
 // CHECK-NEXT:  `-ExprWithCleanups 0x{{[^ ]*}} <{{.*}}> 'const A' lvalue
-// CHECK-NEXT:    `-MaterializeTemporaryExpr 0x{{[^ ]*}} <{{.*}}> 'const A' lvalue extended by Var 0x{{[^ ]*}} 'b' 'B'
+// CHECK-NEXT:    `-MaterializeTemporaryExpr 0x{{[^ ]*}} <{{.*}}> 'const A' lvalue extended by Field 0x{{[^ ]*}} 'a' 'const A &'
 // CHECK-NEXT:      `-ImplicitCastExpr 0x{{[^ ]*}} <{{.*}}> 'const A' <NoOp>
 // CHECK-NEXT:        `-CXXFunctionalCastExpr 0x{{[^ ]*}} <{{.*}}> 'A' functional cast to A <NoOp>
 // CHECK-NEXT:          `-InitListExpr 0x{{[^ ]*}} <{{.*}}> 'A'

clang/test/Analysis/lifetime-extended-regions.cpp

@@ -120,11 +120,10 @@ void aggregateWithReferences() {
   clang_analyzer_dump(viaReference);    // expected-warning-re {{&lifetime_extended_object{RefAggregate, viaReference, S{{[0-9]+}}} }}
   clang_analyzer_dump(viaReference.rx); // expected-warning-re {{&lifetime_extended_object{int, viaReference, S{{[0-9]+}}} }}
   clang_analyzer_dump(viaReference.ry); // expected-warning-re {{&lifetime_extended_object{Composite, viaReference, S{{[0-9]+}}} }}
-  
-  // FIXME: clang currently support extending lifetime of object bound to reference members of aggregates,
-  // that are created from default member initializer. But CFG and ExprEngine need to be updated to address this change.
-  // The following expect warning: {{&lifetime_extended_object{Composite, defaultInitExtended, S{{[0-9]+}}} }}
-  RefAggregate defaultInitExtended{i};
+
+  // clang does not currently implement extending lifetime of object bound to reference members of aggregates,
+  // that are created from default member initializer (see `warn_unsupported_lifetime_extension` from `-Wdangling`)
+  RefAggregate defaultInitExtended{i}; // clang-bug does not extend `Composite`
   clang_analyzer_dump(defaultInitExtended.ry); // expected-warning {{Unknown }}
 }
 

clang/test/CXX/drs/cwg16xx.cpp

@@ -483,6 +483,8 @@ namespace cwg1696 { // cwg1696: 7
     const A &a = A(); // #cwg1696-D1-a
   };
   D1 d1 = {}; // #cwg1696-d1
+  // since-cxx14-warning@-1 {{lifetime extension of temporary created by aggregate initialization using a default member initializer is not yet supported; lifetime of temporary will end at the end of the full-expression}}
+  //   since-cxx14-note@#cwg1696-D1-a {{initializing field 'a' with default member initializer}}
 
   struct D2 {
     const A &a = A(); // #cwg1696-D2-a

clang/test/CXX/drs/cwg18xx.cpp

@@ -56,7 +56,7 @@ namespace cwg1804 { // cwg1804: 2.7
 template <typename, typename>
 struct A {
   void f1();
-  
+
   template <typename V>
   void f2(V);
 
@@ -73,7 +73,7 @@ struct A {
 template <typename U>
 struct A<int, U> {
   void f1();
-  
+
   template <typename V>
   void f2(V);
 
@@ -97,7 +97,7 @@ class D {
 template <typename U>
 struct A<double, U> {
   void f1();
-  
+
   template <typename V>
   void f2(V);
 
@@ -206,28 +206,19 @@ namespace cwg1814 { // cwg1814: yes
 #endif
 }
 
-namespace cwg1815 { // cwg1815: 19
+namespace cwg1815 { // cwg1815: no
 #if __cplusplus >= 201402L
-  struct A { int &&r = 0; };
+  // FIXME: needs codegen test
+  struct A { int &&r = 0; }; // #cwg1815-A
   A a = {};
+  // since-cxx14-warning@-1 {{lifetime extension of temporary created by aggregate initialization using a default member initializer is not yet supported; lifetime of temporary will end at the end of the full-expression}} FIXME
+  //   since-cxx14-note@#cwg1815-A {{initializing field 'r' with default member initializer}}
 
   struct B { int &&r = 0; }; // #cwg1815-B
   // since-cxx14-error@-1 {{reference member 'r' binds to a temporary object whose lifetime would be shorter than the lifetime of the constructed object}}
   //   since-cxx14-note@#cwg1815-B {{initializing field 'r' with default member initializer}}
   //   since-cxx14-note@#cwg1815-b {{in implicit default constructor for 'cwg1815::B' first required here}}
   B b; // #cwg1815-b
-
-#if __cplusplus >= 201703L
-  struct C { const int &r = 0; };
-  constexpr C c = {}; // OK, since cwg1815
-  static_assert(c.r == 0);
-
-  constexpr int f() {
-    A a = {}; // OK, since cwg1815
-    return a.r;
-  }
-  static_assert(f() == 0);
-#endif
 #endif
 }
 

clang/test/CXX/special/class.temporary/p6.cpp

@@ -269,40 +269,6 @@ void init_capture_init_list() {
   // CHECK: }
 }
 
-void check_dr1815() { // dr1815: yes
-#if __cplusplus >= 201402L
-
-  struct A {
-    int &&r = 0;
-    ~A() {}
-  };
-
-  struct B {
-    A &&a = A{};
-    ~B() {}
-  };
-  B a = {};
-  
-  // CHECK: call {{.*}}block_scope_begin_function
-  extern void block_scope_begin_function();
-  extern void block_scope_end_function();
-  block_scope_begin_function();
-  {
-    // CHECK: call void @_ZZ12check_dr1815vEN1BD1Ev
-    // CHECK: call void @_ZZ12check_dr1815vEN1AD1Ev
-    B b = {};
-  }
-  // CHECK: call {{.*}}block_scope_end_function
-  block_scope_end_function();
-
-  // CHECK: call {{.*}}some_other_function
-  extern void some_other_function();
-  some_other_function();
-  // CHECK: call void @_ZZ12check_dr1815vEN1BD1Ev
-  // CHECK: call void @_ZZ12check_dr1815vEN1AD1Ev
-#endif
-}
-
 namespace P2718R0 {
 namespace basic {
 template <typename E> using T2 = std::list<E>;

clang/test/SemaCXX/constexpr-default-arg.cpp

@@ -32,8 +32,8 @@ void test_default_arg2() {
 }
 
 // Check that multiple CXXDefaultInitExprs don't cause an assertion failure.
-struct A { int &&r = 0; };
+struct A { int &&r = 0; }; // expected-note 2{{default member initializer}}
 struct B { A x, y; };
-B b = {}; // expected-no-diagnostics
+B b = {}; // expected-warning 2{{lifetime extension of temporary created by aggregate initialization using a default member initializer is not yet supported}}
 
 }

clang/test/SemaCXX/eval-crashes.cpp

@@ -25,9 +25,11 @@ namespace pr33140_0b {
 }
 
 namespace pr33140_2 {
-  struct A { int &&r = 0; };
+  // FIXME: The declaration of 'b' below should lifetime-extend two int
+  // temporaries.
+  struct A { int &&r = 0; }; // expected-note 2{{initializing field 'r' with default member initializer}}
   struct B { A x, y; };
-  B b = {};
+  B b = {}; // expected-warning 2{{lifetime extension of temporary created by aggregate initialization using a default member initializer is not yet supported}}
 }
 
 namespace pr33140_3 {

clang/www/cxx_dr_status.html

@@ -10698,7 +10698,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
     <td><a href="https://cplusplus.github.io/CWG/issues/1815.html">1815</a></td>
     <td>CD4</td>
     <td>Lifetime extension in aggregate initialization</td>
-    <td class="unreleased" align="center">Clang 19</td>
+    <td class="none" align="center">No</td>
   </tr>
   <tr id="1816">
     <td><a href="https://cplusplus.github.io/CWG/issues/1816.html">1816</a></td>