Index: lib/CodeGen/CGDecl.cpp
===================================================================
--- lib/CodeGen/CGDecl.cpp
+++ lib/CodeGen/CGDecl.cpp
@@ -1599,19 +1599,16 @@
     EnsureInsertPoint();
   }
 
-  // Initialize the structure of a __block variable.
-  if (emission.IsEscapingByRef)
-    emitByrefStructureInit(emission);
-
   // Initialize the variable here if it doesn't have a initializer and it is a
   // C struct that is non-trivial to initialize or an array containing such a
   // struct.
-  if (!Init &&
-      type.isNonTrivialToPrimitiveDefaultInitialize() ==
-          QualType::PDIK_Struct) {
+  if (!Init && type.isNonTrivialToPrimitiveDefaultInitialize() ==
+                   QualType::PDIK_Struct) {
     LValue Dst = MakeAddrLValue(emission.getAllocatedAddress(), type);
-    if (emission.IsEscapingByRef)
+    if (emission.IsEscapingByRef) {
+      emitByrefStructureInit(emission);
       drillIntoBlockVariable(*this, Dst, &D);
+    }
     defaultInitNonTrivialCStructVar(Dst);
     return;
   }
@@ -1633,10 +1630,18 @@
                   ? LangOptions::TrivialAutoVarInitKind::Uninitialized
                   : getContext().getLangOpts().getTrivialAutoVarInit()));
 
-  auto initializeWhatIsTechnicallyUninitialized = [&]() {
+  bool trivialInitializationDone = false;
+  auto initializeWhatIsTechnicallyUninitialized = [&](Address Loc) {
     if (trivialAutoVarInit ==
         LangOptions::TrivialAutoVarInitKind::Uninitialized)
       return;
+    if (trivialInitializationDone)
+      return;
+    trivialInitializationDone = true;
+
+    // Only initialize a __block's storage: we always initialize the header.
+    if (emission.IsEscapingByRef)
+      Loc = emitBlockByrefAddress(Loc, &D, /*follow=*/false);
 
     CharUnits Size = getContext().getTypeSizeInChars(type);
     if (!Size.isZero()) {
@@ -1714,8 +1719,14 @@
     }
   };
 
+  // Initialize the structure of a __block variable.
+  if (emission.IsEscapingByRef) {
+    initializeWhatIsTechnicallyUninitialized(Loc);
+    emitByrefStructureInit(emission);
+  }
+
   if (isTrivialInitializer(Init)) {
-    initializeWhatIsTechnicallyUninitialized();
+    initializeWhatIsTechnicallyUninitialized(Loc);
     return;
   }
 
@@ -1729,7 +1740,7 @@
   }
 
   if (!constant) {
-    initializeWhatIsTechnicallyUninitialized();
+    initializeWhatIsTechnicallyUninitialized(Loc);
     LValue lv = MakeAddrLValue(Loc, type);
     lv.setNonGC(true);
     return EmitExprAsInit(Init, &D, lv, capturedByInit);
Index: test/CodeGenCXX/trivial-auto-var-init.cpp
===================================================================
--- test/CodeGenCXX/trivial-auto-var-init.cpp
+++ test/CodeGenCXX/trivial-auto-var-init.cpp
@@ -30,6 +30,32 @@
   used(block);
 }
 
+// Using the variable being initialized is typically UB in C, but for blocks we
+// can be nice: they imply extra book-keeping and we can do the auto-init before
+// any of said book-keeping.
+//
+// UNINIT-LABEL:  test_block_self_init(
+// ZERO-LABEL:    test_block_self_init(
+// ZERO:          %captured = alloca %struct.__block_byref_captured, align 8
+// ZERO-NEXT:     %block = alloca <{ i8*, i32, i32, i8*, %struct.__block_descriptor*, i8* }>, align 8
+// ZERO-NEXT:     %captured1 = getelementptr inbounds %struct.__block_byref_captured, %struct.__block_byref_captured* %captured, i32 0, i32 4
+// ZERO-NEXT:     store %struct.XYZ* null, %struct.XYZ** %captured1, align 8
+// PATTERN-LABEL: test_block_self_init(
+// PATTERN:       %captured = alloca %struct.__block_byref_captured, align 8
+// PATTERN-NEXT:  %block = alloca <{ i8*, i32, i32, i8*, %struct.__block_descriptor*, i8* }>, align 8
+// PATTERN-NEXT:  %captured1 = getelementptr inbounds %struct.__block_byref_captured, %struct.__block_byref_captured* %captured, i32 0, i32 4
+// PATTERN-NEXT:  store %struct.XYZ* inttoptr (i64 -6148914691236517206 to %struct.XYZ*), %struct.XYZ** %captured1, align 8
+void test_block_self_init() {
+  using Block = void (^)();
+  typedef struct XYZ {
+    Block block;
+  } * xyz_t;
+  extern xyz_t create(Block block);
+  __block xyz_t captured = create(^() {
+    (void)captured;
+  });
+}
+
 // This type of code is currently not handled by zero / pattern initialization.
 // The test will break when that is fixed.
 // UNINIT-LABEL:  test_goto_unreachable_value(
Index: test/CodeGenObjC/arc-blocks.m
===================================================================
--- test/CodeGenObjC/arc-blocks.m
+++ test/CodeGenObjC/arc-blocks.m
@@ -122,11 +122,11 @@
   // CHECK-LABEL:    define void @test4()
   // CHECK:      [[VAR:%.*]] = alloca [[BYREF_T:%.*]],
   // CHECK-NEXT: [[BLOCK:%.*]] = alloca [[BLOCK_T:<{.*}>]],
+  // CHECK:      [[SLOT:%.*]] = getelementptr inbounds [[BYREF_T]], [[BYREF_T]]* [[VAR]], i32 0, i32 6
   // CHECK:      [[T0:%.*]] = getelementptr inbounds [[BYREF_T]], [[BYREF_T]]* [[VAR]], i32 0, i32 2
   // 0x02000000 - has copy/dispose helpers strong
   // CHECK-NEXT: store i32 838860800, i32* [[T0]]
-  // CHECK:      [[SLOT:%.*]] = getelementptr inbounds [[BYREF_T]], [[BYREF_T]]* [[VAR]], i32 0, i32 6
-  // CHECK-NEXT: [[T0:%.*]] = call i8* @test4_source()
+  // CHECK:      [[T0:%.*]] = call i8* @test4_source()
   // CHECK-NEXT: [[T1:%.*]] = call i8* @llvm.objc.retainAutoreleasedReturnValue(i8* [[T0]])
   // CHECK-NEXT: store i8* [[T1]], i8** [[SLOT]]
   // CHECK-NEXT: [[SLOT:%.*]] = getelementptr inbounds [[BYREF_T]], [[BYREF_T]]* [[VAR]], i32 0, i32 6
@@ -207,11 +207,11 @@
   // CHECK-NEXT: [[BLOCK:%.*]] = alloca [[BLOCK_T:<{.*}>]],
   // CHECK-NEXT: [[VARPTR1:%.*]] = bitcast [[BYREF_T]]* [[VAR]] to i8*
   // CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 48, i8* [[VARPTR1]])
+  // CHECK:      [[SLOT:%.*]] = getelementptr inbounds [[BYREF_T]], [[BYREF_T]]* [[VAR]], i32 0, i32 6
   // CHECK:      [[T0:%.*]] = getelementptr inbounds [[BYREF_T]], [[BYREF_T]]* [[VAR]], i32 0, i32 2
   // 0x02000000 - has copy/dispose helpers weak
   // CHECK-NEXT: store i32 1107296256, i32* [[T0]]
-  // CHECK:      [[SLOT:%.*]] = getelementptr inbounds [[BYREF_T]], [[BYREF_T]]* [[VAR]], i32 0, i32 6
-  // CHECK-NEXT: [[T0:%.*]] = call i8* @test6_source()
+  // CHECK:      [[T0:%.*]] = call i8* @test6_source()
   // CHECK-NEXT: [[T1:%.*]] = call i8* @llvm.objc.retainAutoreleasedReturnValue(i8* [[T0]])
   // CHECK-NEXT: call i8* @llvm.objc.initWeak(i8** [[SLOT]], i8* [[T1]])
   // CHECK-NEXT: call void @llvm.objc.release(i8* [[T1]])
@@ -219,7 +219,7 @@
   // 0x42800000 - has signature, copy/dispose helpers, as well as BLOCK_HAS_EXTENDED_LAYOUT
   // CHECK:      store i32 -1040187392,
   // CHECK: %[[BLOCK_DESCRIPTOR:.*]] = getelementptr inbounds <{ i8*, i32, i32, i8*, %[[STRUCT_BLOCK_DESCRIPTOR]]*, i8* }>, <{ i8*, i32, i32, i8*, %[[STRUCT_BLOCK_DESCRIPTOR]]*, i8* }>* %{{.*}}, i32 0, i32 4
-// CHECK: store %[[STRUCT_BLOCK_DESCRIPTOR]]* bitcast ({ i64, i64, i8*, i8*, i8*, i64 }* @[[BLOCK_DESCRIPTOR_TMP9]] to %[[STRUCT_BLOCK_DESCRIPTOR]]*), %[[STRUCT_BLOCK_DESCRIPTOR]]** %[[BLOCK_DESCRIPTOR]], align 8
+  // CHECK: store %[[STRUCT_BLOCK_DESCRIPTOR]]* bitcast ({ i64, i64, i8*, i8*, i8*, i64 }* @[[BLOCK_DESCRIPTOR_TMP9]] to %[[STRUCT_BLOCK_DESCRIPTOR]]*), %[[STRUCT_BLOCK_DESCRIPTOR]]** %[[BLOCK_DESCRIPTOR]], align 8
   // CHECK:      [[T0:%.*]] = bitcast [[BYREF_T]]* [[VAR]] to i8*
   // CHECK-NEXT: store i8* [[T0]], i8**
   // CHECK:      call void @test6_helper(
@@ -401,10 +401,10 @@
 
   // CHECK-LABEL:    define void @test10b()
   // CHECK:      [[BYREF:%.*]] = alloca [[BYREF_T:%.*]],
+  // CHECK:      [[T0:%.*]] = getelementptr inbounds [[BYREF_T]], [[BYREF_T]]* [[BYREF]], i32 0, i32 6
 
   // Zero-initialize.
-  // CHECK:      [[T0:%.*]] = getelementptr inbounds [[BYREF_T]], [[BYREF_T]]* [[BYREF]], i32 0, i32 6
-  // CHECK-NEXT: store void ()* null, void ()** [[T0]], align 8
+  // CHECK:      store void ()* null, void ()** [[T0]], align 8
 
   // CHECK-NEXT: [[SLOT:%.*]] = getelementptr inbounds [[BYREF_T]], [[BYREF_T]]* [[BYREF]], i32 0, i32 6
 
Index: test/CodeGenObjC/blocks-2.m
===================================================================
--- test/CodeGenObjC/blocks-2.m
+++ test/CodeGenObjC/blocks-2.m
@@ -20,7 +20,7 @@
 
   // CHECK:      [[N:%.*]] = alloca [[N_T:%.*]], align 8
   // CHECK:      [[T0:%.*]] = getelementptr inbounds [[N_T]], [[N_T]]* [[N]], i32 0, i32 4
-  // CHECK-NEXT: store double 1.000000e+{{0?}}01, double* [[T0]], align 8
+  // CHECK:      store double 1.000000e+{{0?}}01, double* [[T0]], align 8
   __block double n = 10;
 
   // CHECK:      invoke void @{{.*}}test1_help
Index: test/CodeGenObjC/blocks.m
===================================================================
--- test/CodeGenObjC/blocks.m
+++ test/CodeGenObjC/blocks.m
@@ -48,6 +48,7 @@
   // CHECK-NEXT: [[WEAKX:%.*]] = alloca [[WEAK_T:%.*]],
   // CHECK-NEXT: [[BLOCK:%.*]] = alloca [[BLOCK_T:<{.*}>]],
   // CHECK-NEXT: store [[TEST2]]*
+  // CHECK-NEXT: [[T6:%.*]] = getelementptr inbounds [[WEAK_T]], [[WEAK_T]]* [[WEAKX]], i32 0, i32 6
 
   // isa=1 for weak byrefs.
   // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[WEAK_T]], [[WEAK_T]]* [[WEAKX]], i32 0, i32 0
@@ -72,7 +73,6 @@
   // CHECK-NEXT: store i8* bitcast (void (i8*)* @__Block_byref_object_dispose_{{.*}} to i8*), i8** [[T5]]
 
   // Actually capture the value.
-  // CHECK-NEXT: [[T6:%.*]] = getelementptr inbounds [[WEAK_T]], [[WEAK_T]]* [[WEAKX]], i32 0, i32 6
   // CHECK-NEXT: [[CAPTURE:%.*]] = load [[TEST2]]*, [[TEST2]]** [[X]]
   // CHECK-NEXT: store [[TEST2]]* [[CAPTURE]], [[TEST2]]** [[T6]]
 
Index: test/CodeGenObjCXX/arc-blocks.mm
===================================================================
--- test/CodeGenObjCXX/arc-blocks.mm
+++ test/CodeGenObjCXX/arc-blocks.mm
@@ -24,14 +24,14 @@
   }
   // CHECK-LABEL:    define void @_ZN5test03fooEv() 
   // CHECK:      [[V:%.*]] = alloca [[BYREF_A:%.*]], align 8
+  // CHECK:      [[V1:%.*]] = getelementptr inbounds [[BYREF_A]], [[BYREF_A]]* [[V]], i32 0, i32 7
   // CHECK:      [[T0:%.*]] = getelementptr inbounds [[BYREF_A]], [[BYREF_A]]* [[V]], i32 0, i32 4
   // CHECK-NEXT: store i8* bitcast (void (i8*, i8*)* [[COPY_HELPER:@.*]] to i8*), i8** [[T0]]
   // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[BYREF_A]], [[BYREF_A]]* [[V]], i32 0, i32 5
   // CHECK-NEXT: store i8* bitcast (void (i8*)* [[DISPOSE_HELPER:@.*]] to i8*), i8** [[T0]]
   // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[BYREF_A]], [[BYREF_A]]* [[V]], i32 0, i32 6
   // CHECK-NEXT: store i8* getelementptr inbounds ([3 x i8], [3 x i8]* [[LAYOUT0]], i32 0, i32 0), i8** [[T0]]
-  // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[BYREF_A]], [[BYREF_A]]* [[V]], i32 0, i32 7
-  // CHECK-NEXT: call void @_ZN5test01AC1Ev([[A]]* [[T0]])
+  // CHECK-NEXT: call void @_ZN5test01AC1Ev([[A]]* [[V1]])
   // CHECK-NEXT: [[T0:%.*]] = getelementptr inbounds [[BYREF_A]], [[BYREF_A]]* [[V]], i32 0, i32 7
   // CHECK: bitcast [[BYREF_A]]* [[V]] to i8*
   // CHECK: [[T1:%.*]] = bitcast [[BYREF_A]]* [[V]] to i8*