Index: lib/CodeGen/CGExprConstant.cpp
===================================================================
--- lib/CodeGen/CGExprConstant.cpp
+++ lib/CodeGen/CGExprConstant.cpp
@@ -47,7 +47,7 @@
 public:
   static llvm::Constant *BuildStruct(ConstantEmitter &Emitter,
                                      ConstExprEmitter *ExprEmitter,
-                                     llvm::ConstantStruct *Base,
+                                     llvm::Constant *Base,
                                      InitListExpr *Updater,
                                      QualType ValTy);
   static llvm::Constant *BuildStruct(ConstantEmitter &Emitter,
@@ -76,7 +76,7 @@
   void ConvertStructToPacked();
 
   bool Build(InitListExpr *ILE);
-  bool Build(ConstExprEmitter *Emitter, llvm::ConstantStruct *Base,
+  bool Build(ConstExprEmitter *Emitter, llvm::Constant *Base,
              InitListExpr *Updater);
   bool Build(const APValue &Val, const RecordDecl *RD, bool IsPrimaryBase,
              const CXXRecordDecl *VTableClass, CharUnits BaseOffset);
@@ -566,7 +566,7 @@
 
 llvm::Constant *ConstStructBuilder::BuildStruct(ConstantEmitter &Emitter,
                                                 ConstExprEmitter *ExprEmitter,
-                                                llvm::ConstantStruct *Base,
+                                                llvm::Constant *Base,
                                                 InitListExpr *Updater,
                                                 QualType ValTy) {
   ConstStructBuilder Builder(Emitter);
@@ -1027,8 +1027,8 @@
     }
 
     if (destType->isRecordType())
-      return ConstStructBuilder::BuildStruct(Emitter, this,
-                 dyn_cast<llvm::ConstantStruct>(Base), Updater, destType);
+      return ConstStructBuilder::BuildStruct(Emitter, this, Base, Updater,
+                                             destType);
 
     return nullptr;
   }
@@ -1103,7 +1103,7 @@
 }  // end anonymous namespace.
 
 bool ConstStructBuilder::Build(ConstExprEmitter *ExprEmitter,
-                               llvm::ConstantStruct *Base,
+                               llvm::Constant *Base,
                                InitListExpr *Updater) {
   assert(Base && "base expression should not be empty");
 
@@ -1111,7 +1111,7 @@
   RecordDecl *RD = ExprType->getAs<RecordType>()->getDecl();
   const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
   const llvm::StructLayout *BaseLayout = CGM.getDataLayout().getStructLayout(
-                                           Base->getType());
+      cast<llvm::StructType>(Base->getType()));
   unsigned FieldNo = -1;
   unsigned ElementNo = 0;
 
@@ -1132,7 +1132,7 @@
     if (Field->isUnnamedBitfield())
       continue;
 
-    llvm::Constant *EltInit = Base->getOperand(ElementNo);
+    llvm::Constant *EltInit = Base->getAggregateElement(ElementNo);
 
     // Bail out if the type of the ConstantStruct does not have the same layout
     // as the type of the InitListExpr.
Index: test/CodeGen/designated-initializers.c
===================================================================
--- test/CodeGen/designated-initializers.c
+++ test/CodeGen/designated-initializers.c
@@ -142,6 +142,18 @@
 // CHECK: @lab = global { [4 x i8], i32 } { [4 x i8] undef, i32 123 }
 struct leading_anon_bitfield { int : 32; int n; } lab = { .n = 123 };
 
+// rdar://45691981
+struct Base {
+  struct {
+    int A;
+  };
+};
+struct Derived {
+  struct Base B;
+};
+struct Derived D = {{}, .B.A = 42};
+// CHECK: @D = global %struct.Derived { %struct.Base { %struct.anon.4 { i32 42 } } }, align 4
+
 void test1(int argc, char **argv)
 {
   // CHECK: internal global %struct.foo { i8* null, i32 1024 }
@@ -149,7 +161,7 @@
     .b = 1024,
   };
 
-  // CHECK: bitcast %union.anon.4* %u2
+  // CHECK: bitcast %union.anon.5* %u2
   // CHECK: call void @llvm.memset
    union { int i; float f; } u2 = { };