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

lambda capture used by the created block

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 commit fixes the conversion by avoiding
copy elision for the capture that captures the lambda that's used in the block
created by the lambda to block conversion process.

rdar://31385153

Differential Revision: https://reviews.llvm.org/D31669

llvm-svn: 299646

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -1689,8 +1689,8 @@ 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"

clang/include/clang/Sema/Initialization.h

@@ -70,6 +70,9 @@ public:
     /// \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,
@@ -261,6 +264,12 @@ public:
     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) {

clang/lib/Sema/SemaInit.cpp

@@ -950,6 +950,7 @@ static void warnBracedScalarInit(Sema &S, const InitializedEntity &Entity,
   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");
   }
@@ -2934,6 +2935,7 @@ DeclarationName InitializedEntity::getName() const {
   case EK_VectorElement:
   case EK_ComplexElement:
   case EK_BlockElement:
+  case EK_LambdaToBlockConversionBlockElement:
   case EK_CompoundLiteralInit:
   case EK_RelatedResult:
     return DeclarationName();
@@ -2963,6 +2965,7 @@ ValueDecl *InitializedEntity::getDecl() const {
   case EK_VectorElement:
   case EK_ComplexElement:
   case EK_BlockElement:
+  case EK_LambdaToBlockConversionBlockElement:
   case EK_LambdaCapture:
   case EK_CompoundLiteralInit:
   case EK_RelatedResult:
@@ -2992,6 +2995,7 @@ bool InitializedEntity::allowsNRVO() const {
   case EK_VectorElement:
   case EK_ComplexElement:
   case EK_BlockElement:
+  case EK_LambdaToBlockConversionBlockElement:
   case EK_LambdaCapture:
   case EK_RelatedResult:
     break;
@@ -3025,6 +3029,9 @@ unsigned InitializedEntity::dumpImpl(raw_ostream &OS) const {
   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);
@@ -3622,9 +3629,13 @@ static void TryConstructorInitialization(Sema &S,
   //       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.
@@ -5488,6 +5499,7 @@ getAssignmentAction(const InitializedEntity &Entity, bool Diagnose = false) {
   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;
@@ -5511,6 +5523,7 @@ static bool shouldBindAsTemporary(const InitializedEntity &Entity) {
   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;
@@ -5537,6 +5550,7 @@ static bool shouldDestroyEntity(const InitializedEntity &Entity) {
     case InitializedEntity::EK_VectorElement:
     case InitializedEntity::EK_ComplexElement:
     case InitializedEntity::EK_BlockElement:
+    case InitializedEntity::EK_LambdaToBlockConversionBlockElement:
     case InitializedEntity::EK_LambdaCapture:
       return false;
 
@@ -5584,6 +5598,7 @@ static SourceLocation getInitializationLoc(const InitializedEntity &Entity,
   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();
@@ -6021,6 +6036,7 @@ InitializedEntityOutlivesFullExpression(const InitializedEntity &Entity) {
   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.
@@ -6109,6 +6125,7 @@ static const InitializedEntity *getEntityForTemporaryLifetimeExtension(
     return FallbackDecl;
 
   case InitializedEntity::EK_BlockElement:
+  case InitializedEntity::EK_LambdaToBlockConversionBlockElement:
   case InitializedEntity::EK_LambdaCapture:
   case InitializedEntity::EK_Exception:
   case InitializedEntity::EK_VectorElement:

clang/lib/Sema/SemaLambda.cpp

@@ -1649,8 +1649,7 @@ ExprResult Sema::BuildBlockForLambdaConversion(SourceLocation CurrentLocation,
   CallOperator->markUsed(Context);
 
   ExprResult Init = PerformCopyInitialization(
-                      InitializedEntity::InitializeBlock(ConvLocation, 
-                                                         Src->getType(), 
+      InitializedEntity::InitializeLambdaToBlock(ConvLocation, Src->getType(),
                                                  /*NRVO=*/false),
       CurrentLocation, Src);
   if (!Init.isInvalid())

clang/test/CodeGenObjCXX/lambda-to-block.mm

@@ -0,0 +1,18 @@
+// 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_