Fix lambda to block conversion in C++17 by avoiding copy elision for the lambda capture used by the created block

[arphaman]

Summary

The commit r288866 introduced guaranteed copy elision to C++ 17. This unfortunately broke the lambda to block conversion in C++17 (the compiler crashes when performing IRGen). This patch fixes the conversion by avoiding copy elision for the capture that captures the lambda that's used in the block created by lambda to block conversion process.

[aprantl]

include/clang/Sema/Initialization.h

122 ↗

(On Diff #94067)

No need to use \brief any more. LLVM uses autobrief.

[rjmccall]

include/clang/Sema/Initialization.h

124 ↗

(On Diff #94067)

It seems less invasive to just give this a new EntityKind.

[arphaman]

Use a new EntityKind and improve test.

[rjmccall]

Looks good, thanks.

cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td

 def err_destructor_template : Error<
   "destructor cannot be declared as a template">;
 
 // C++ initialization
 def err_init_conversion_failed : Error<
   "cannot initialize %select{a variable|a parameter|return object|an "
   "exception object|a member subobject|an array element|a new value|a value|a "
   "base class|a constructor delegation|a vector element|a block element|a "
-  "complex element|a lambda capture|a compound literal initializer|a "
-  "related result|a parameter of CF audited function}0 "
+  "block element|a complex element|a lambda capture|a compound literal "
+  "initializer|a related result|a parameter of CF audited function}0 "
   "%diff{of type $ with an %select{rvalue|lvalue}2 of type $|"
   "with an %select{rvalue|lvalue}2 of incompatible type}1,3"
   "%select{|: different classes%diff{ ($ vs $)|}5,6"
   "|: different number of parameters (%5 vs %6)"
   "|: type mismatch at %ordinal5 parameter%diff{ ($ vs $)|}6,7"
   "|: different return type%diff{ ($ vs $)|}5,6"
   "|: different qualifiers ("
   "%select{none|const|restrict|const and restrict|volatile|const and volatile|"

cfe/trunk/include/clang/Sema/Initialization.h

enum EntityKind {
     /// \brief The initialization is being done by a delegating constructor.
     EK_Delegating,
     /// \brief The entity being initialized is an element of a vector.
     /// or vector.
     EK_VectorElement,
     /// \brief The entity being initialized is a field of block descriptor for
     /// the copied-in c++ object.
     EK_BlockElement,
+    /// The entity being initialized is a field of block descriptor for the
+    /// copied-in lambda object that's used in the lambda to block conversion.
+    EK_LambdaToBlockConversionBlockElement,
     /// \brief The entity being initialized is the real or imaginary part of a
     /// complex number.
     EK_ComplexElement,
     /// \brief The entity being initialized is the field that captures a 
     /// variable in a lambda.
     EK_LambdaCapture,
     /// \brief The entity being initialized is the initializer for a compound
     /// literal.
static InitializedEntity InitializeResult(SourceLocation ReturnLoc,
                                             QualType Type, bool NRVO) {
     return InitializedEntity(EK_Result, ReturnLoc, Type, NRVO);
   }
 
   static InitializedEntity InitializeBlock(SourceLocation BlockVarLoc,
                                            QualType Type, bool NRVO) {
     return InitializedEntity(EK_BlockElement, BlockVarLoc, Type, NRVO);
   }
-  
+  static InitializedEntity InitializeLambdaToBlock(SourceLocation BlockVarLoc,
+                                                   QualType Type, bool NRVO) {
+    return InitializedEntity(EK_LambdaToBlockConversionBlockElement,
+                             BlockVarLoc, Type, NRVO);
+  }
+
   /// \brief Create the initialization entity for an exception object.
   static InitializedEntity InitializeException(SourceLocation ThrowLoc,
                                                QualType Type, bool NRVO) {
     return InitializedEntity(EK_Exception, ThrowLoc, Type, NRVO);
   }
 
   /// \brief Create the initialization entity for an object allocated via new.
   static InitializedEntity InitializeNew(SourceLocation NewLoc, QualType Type) {

cfe/trunk/lib/Sema/SemaInit.cpp

static void warnBracedScalarInit(Sema &S, const InitializedEntity &Entity,
   case InitializedEntity::EK_RelatedResult:
     // No warning, we already warned when initializing the result.
     break;
 
   case InitializedEntity::EK_Exception:
   case InitializedEntity::EK_Base:
   case InitializedEntity::EK_Delegating:
   case InitializedEntity::EK_BlockElement:
+  case InitializedEntity::EK_LambdaToBlockConversionBlockElement:
   case InitializedEntity::EK_Binding:
     llvm_unreachable("unexpected braced scalar init");
   }
 
   if (DiagID) {
     S.Diag(Braces.getBegin(), DiagID)
       << Braces
       << FixItHint::CreateRemoval(Braces.getBegin())
DeclarationName InitializedEntity::getName() const {
   case EK_New:
   case EK_Temporary:
   case EK_Base:
   case EK_Delegating:
   case EK_ArrayElement:
   case EK_VectorElement:
   case EK_ComplexElement:
   case EK_BlockElement:
+  case EK_LambdaToBlockConversionBlockElement:
   case EK_CompoundLiteralInit:
   case EK_RelatedResult:
     return DeclarationName();
   }
 
   llvm_unreachable("Invalid EntityKind!");
 }
 
ValueDecl *InitializedEntity::getDecl() const {
   case EK_New:
   case EK_Temporary:
   case EK_Base:
   case EK_Delegating:
   case EK_ArrayElement:
   case EK_VectorElement:
   case EK_ComplexElement:
   case EK_BlockElement:
+  case EK_LambdaToBlockConversionBlockElement:
   case EK_LambdaCapture:
   case EK_CompoundLiteralInit:
   case EK_RelatedResult:
     return nullptr;
   }
 
   llvm_unreachable("Invalid EntityKind!");
 }
bool InitializedEntity::allowsNRVO() const {
   case EK_Temporary:
   case EK_CompoundLiteralInit:
   case EK_Base:
   case EK_Delegating:
   case EK_ArrayElement:
   case EK_VectorElement:
   case EK_ComplexElement:
   case EK_BlockElement:
+  case EK_LambdaToBlockConversionBlockElement:
   case EK_LambdaCapture:
   case EK_RelatedResult:
     break;
   }
 
   return false;
 }
 
unsigned InitializedEntity::dumpImpl(raw_ostream &OS) const {
   case EK_CompoundLiteralInit: OS << "CompoundLiteral";break;
   case EK_RelatedResult: OS << "RelatedResult"; break;
   case EK_Base: OS << "Base"; break;
   case EK_Delegating: OS << "Delegating"; break;
   case EK_ArrayElement: OS << "ArrayElement " << Index; break;
   case EK_VectorElement: OS << "VectorElement " << Index; break;
   case EK_ComplexElement: OS << "ComplexElement " << Index; break;
   case EK_BlockElement: OS << "Block"; break;
+  case EK_LambdaToBlockConversionBlockElement:
+    OS << "Block (lambda)";
+    break;
   case EK_LambdaCapture:
     OS << "LambdaCapture ";
     OS << DeclarationName(Capture.VarID);
     break;
   }
 
   if (auto *D = getDecl()) {
     OS << " ";
static void TryConstructorInitialization(Sema &S,
 
   // C++1z [dcl.init]p17:
   //     - If the initializer expression is a prvalue and the cv-unqualified
   //       version of the source type is the same class as the class of the
   //       destination, the initializer expression is used to initialize the
   //       destination object.
   // Per DR (no number yet), this does not apply when initializing a base
   // class or delegating to another constructor from a mem-initializer.
+  // ObjC++: Lambda captured by the block in the lambda to block conversion
+  // should avoid copy elision.
   if (S.getLangOpts().CPlusPlus1z &&
       Entity.getKind() != InitializedEntity::EK_Base &&
       Entity.getKind() != InitializedEntity::EK_Delegating &&
+      Entity.getKind() !=
+          InitializedEntity::EK_LambdaToBlockConversionBlockElement &&
       UnwrappedArgs.size() == 1 && UnwrappedArgs[0]->isRValue() &&
       S.Context.hasSameUnqualifiedType(UnwrappedArgs[0]->getType(), DestType)) {
     // Convert qualifications if necessary.
     Sequence.AddQualificationConversionStep(DestType, VK_RValue);
     if (ILE)
       Sequence.RewrapReferenceInitList(DestType, ILE);
     return;
   }
case InitializedEntity::EK_RelatedResult:
     return Sema::AA_Casting;
 
   case InitializedEntity::EK_Member:
   case InitializedEntity::EK_Binding:
   case InitializedEntity::EK_ArrayElement:
   case InitializedEntity::EK_VectorElement:
   case InitializedEntity::EK_ComplexElement:
   case InitializedEntity::EK_BlockElement:
+  case InitializedEntity::EK_LambdaToBlockConversionBlockElement:
   case InitializedEntity::EK_LambdaCapture:
   case InitializedEntity::EK_CompoundLiteralInit:
     return Sema::AA_Initializing;
   }
 
   llvm_unreachable("Invalid EntityKind!");
 }
 
 /// \brief Whether we should bind a created object as a temporary when
 /// initializing the given entity.
 static bool shouldBindAsTemporary(const InitializedEntity &Entity) {
   switch (Entity.getKind()) {
   case InitializedEntity::EK_ArrayElement:
   case InitializedEntity::EK_Member:
   case InitializedEntity::EK_Result:
   case InitializedEntity::EK_New:
   case InitializedEntity::EK_Variable:
   case InitializedEntity::EK_Base:
   case InitializedEntity::EK_Delegating:
   case InitializedEntity::EK_VectorElement:
   case InitializedEntity::EK_ComplexElement:
   case InitializedEntity::EK_Exception:
   case InitializedEntity::EK_BlockElement:
+  case InitializedEntity::EK_LambdaToBlockConversionBlockElement:
   case InitializedEntity::EK_LambdaCapture:
   case InitializedEntity::EK_CompoundLiteralInit:
     return false;
 
   case InitializedEntity::EK_Parameter:
   case InitializedEntity::EK_Parameter_CF_Audited:
   case InitializedEntity::EK_Temporary:
   case InitializedEntity::EK_RelatedResult:
static bool shouldDestroyEntity(const InitializedEntity &Entity) {
   switch (Entity.getKind()) {
     case InitializedEntity::EK_Result:
     case InitializedEntity::EK_New:
     case InitializedEntity::EK_Base:
     case InitializedEntity::EK_Delegating:
     case InitializedEntity::EK_VectorElement:
     case InitializedEntity::EK_ComplexElement:
     case InitializedEntity::EK_BlockElement:
+    case InitializedEntity::EK_LambdaToBlockConversionBlockElement:
     case InitializedEntity::EK_LambdaCapture:
       return false;
 
     case InitializedEntity::EK_Member:
     case InitializedEntity::EK_Binding:
     case InitializedEntity::EK_Variable:
     case InitializedEntity::EK_Parameter:
     case InitializedEntity::EK_Parameter_CF_Audited:
static SourceLocation getInitializationLoc(const InitializedEntity &Entity,
   case InitializedEntity::EK_Parameter_CF_Audited:
   case InitializedEntity::EK_Temporary:
   case InitializedEntity::EK_New:
   case InitializedEntity::EK_Base:
   case InitializedEntity::EK_Delegating:
   case InitializedEntity::EK_VectorElement:
   case InitializedEntity::EK_ComplexElement:
   case InitializedEntity::EK_BlockElement:
+  case InitializedEntity::EK_LambdaToBlockConversionBlockElement:
   case InitializedEntity::EK_CompoundLiteralInit:
   case InitializedEntity::EK_RelatedResult:
     return Initializer->getLocStart();
   }
   llvm_unreachable("missed an InitializedEntity kind?");
 }
 
 /// \brief Make a (potentially elidable) temporary copy of the object
InitializedEntityOutlivesFullExpression(const InitializedEntity &Entity) {
   case InitializedEntity::EK_New:
   case InitializedEntity::EK_Base:
   case InitializedEntity::EK_Delegating:
     return true;
 
   case InitializedEntity::EK_ArrayElement:
   case InitializedEntity::EK_VectorElement:
   case InitializedEntity::EK_BlockElement:
+  case InitializedEntity::EK_LambdaToBlockConversionBlockElement:
   case InitializedEntity::EK_ComplexElement:
     // Could not determine what the full initialization is. Assume it might not
     // outlive the full-expression.
     return false;
 
   case InitializedEntity::EK_Parameter:
   case InitializedEntity::EK_Parameter_CF_Audited:
   case InitializedEntity::EK_Temporary:
static const InitializedEntity *getEntityForTemporaryLifetimeExtension(
   case InitializedEntity::EK_Delegating:
     // We can reach this case for aggregate initialization in a constructor:
     //   struct A { int &&r; };
     //   struct B : A { B() : A{0} {} };
     // In this case, use the innermost field decl as the context.
     return FallbackDecl;
 
   case InitializedEntity::EK_BlockElement:
+  case InitializedEntity::EK_LambdaToBlockConversionBlockElement:
   case InitializedEntity::EK_LambdaCapture:
   case InitializedEntity::EK_Exception:
   case InitializedEntity::EK_VectorElement:
   case InitializedEntity::EK_ComplexElement:
     return nullptr;
   }
   llvm_unreachable("unknown entity kind");
 }

cfe/trunk/lib/Sema/SemaLambda.cpp

ExprResult Sema::BuildBlockForLambdaConversion(SourceLocation CurrentLocation,
   CXXMethodDecl *CallOperator 
     = cast<CXXMethodDecl>(
         Lambda->lookup(
           Context.DeclarationNames.getCXXOperatorName(OO_Call)).front());
   CallOperator->setReferenced();
   CallOperator->markUsed(Context);
 
   ExprResult Init = PerformCopyInitialization(
-                      InitializedEntity::InitializeBlock(ConvLocation, 
-                                                         Src->getType(), 
-                                                         /*NRVO=*/false),
-                      CurrentLocation, Src);
+      InitializedEntity::InitializeLambdaToBlock(ConvLocation, Src->getType(),
   if (!Init.isInvalid())
     Init = ActOnFinishFullExpr(Init.get());
   
   if (Init.isInvalid())
     return ExprError();
   
   // Create the new block to be returned.
   BlockDecl *Block = BlockDecl::Create(Context, CurContext, ConvLocation);

cfe/trunk/test/CodeGenObjCXX/lambda-to-block.mm

+// RUN: %clang_cc1 -x objective-c++ -fblocks -triple x86_64-apple-darwin10 -fobjc-runtime=macosx-fragile-10.5 -std=c++1z -emit-llvm -o - %s | FileCheck %s
+
+// rdar://31385153
+// Shouldn't crash!
+
+void takesBlock(void (^)(void));
+
+struct Copyable {
+  Copyable(const Copyable &x);
+};
+
+void hasLambda(Copyable x) {
+  takesBlock([x] () { });
+}
+// CHECK-LABEL: define internal void @__copy_helper_block_
+// CHECK: call void @"_ZZ9hasLambda8CopyableEN3$_0C1ERKS0_"
+// CHECK-LABEL: define internal void @"_ZZ9hasLambda8CopyableEN3$_0C2ERKS0_"
+// CHECK: call void @_ZN8CopyableC1ERKS_