Revert r21706 "Stop checking for 'nil' returns from non-failable Objective-C initializers."

Swift SVN r21712

Author: DougGregor

lib/SILGen/SILGenExpr.cpp

@@ -4641,6 +4641,30 @@ RValue RValueEmitter::visitRebindSelfInConstructorExpr(
     break;
   }
   SGF.SelfInitDelegationState = SILGenFunction::NormalSelf;
+
+  // If we are using Objective-C allocation, the caller can return
+  // nil. When this happens with an explicitly-written super.init or
+  // self.init invocation, return early if we did get nil.
+  //
+  // TODO: Remove this when failable initializers are fully implemented.
+  auto classDecl = selfTy->getClassOrBoundGenericClass();
+  if (classDecl && !E->getSubExpr()->isImplicit() &&
+      usesObjCAllocator(classDecl)) {
+    // Check whether the new self is null.
+    SILValue isNonnullSelf = SGF.B.createIsNonnull(E, newSelf.getValue());
+    Condition cond = SGF.emitCondition(isNonnullSelf, E, 
+                                       /*hasFalseCode=*/false,
+                                       /*invertValue=*/true,
+                                       { });
+
+    // If self is null, branch to the epilog.
+    cond.enterTrue(SGF.B);
+    SGF.Cleanups.emitBranchAndCleanups(SGF.ReturnDest, E, { });
+    cond.exitTrue(SGF.B);
+
+    cond.complete(SGF.B);
+  }
+
   return SGF.emitEmptyTupleRValue(E);
 }
 

test/SILGen/objc_thunks.swift

@@ -193,8 +193,17 @@ class Hoozit : Gizmo {
   // CHECK-NOT: unconditional_checked_cast downcast [[SELF_REPLACED]] : $Gizmo to $Hoozit
   // CHECK: unchecked_ref_cast
   // CHECK-NEXT: store [[SELF:%[0-9]+]] to [[SELF_BOX]]#1 : $*Hoozit
+  // CHECK-NEXT: [[NONNULL:%[0-9]+]] = is_nonnull [[SELF]] : $Hoozit
+  // CHECK-NEXT: cond_br [[NONNULL]], [[NONNULL_BB:bb[0-9]+]], [[NULL_BB:bb[0-9]+]]
+  // CHECK: [[NULL_BB]]:
+  // CHECK:   br [[EPILOG_BB:bb[0-9]+]]
+
+  // CHECK: [[NONNULL_BB]]:
   // CHECK:   [[OTHER_REF:%[0-9]+]] = function_ref @_TF11objc_thunks5otherFT_T_ : $@thin () -> ()
   // CHECK-NEXT: apply [[OTHER_REF]]() : $@thin () -> ()
+  // CHECK-NEXT: br [[EPILOG_BB]]
+
+  // CHECK: [[EPILOG_BB]]:
   // CHECK-NOT: super_method
   // CHECK: return
   override init(bellsOn x : Int) {
@@ -259,9 +268,19 @@ extension Hoozit {
     // CHECK: [[CTOR:%[0-9]+]] = class_method [volatile] [[SELF:%[0-9]+]] : $Hoozit, #Hoozit.init!initializer.1.foreign : Hoozit.Type -> (int: Int) -> Hoozit , $@cc(objc_method) @thin (Int, @owned Hoozit) -> @owned Hoozit
     // CHECK: [[NEW_SELF:%[0-9]+]] = apply [[CTOR]]
     // CHECK: store [[NEW_SELF]] to [[SELF_BOX]]#1 : $*Hoozit
-    // CHECK: [[OTHER_REF:%[0-9]+]] = function_ref @_TF11objc_thunks5otherFT_T_ : $@thin () -> ()
+    // CHECK: [[NONNULL:%[0-9]+]] = is_nonnull [[NEW_SELF]] : $Hoozit
+    // CHECK-NEXT: cond_br [[NONNULL]], [[NONNULL_BB:bb[0-9]+]], [[NULL_BB:bb[0-9]+]]
+    // CHECK: [[NULL_BB]]:
+    // CHECK-NEXT: strong_release [[X_BOX]]#0 : $Builtin.NativeObject
+    // CHECK-NEXT: br [[EPILOG_BB:bb[0-9]+]]
+
+    // CHECK: [[NONNULL_BB]]:
+    // CHECK:   [[OTHER_REF:%[0-9]+]] = function_ref @_TF11objc_thunks5otherFT_T_ : $@thin () -> ()
     // CHECK-NEXT: apply [[OTHER_REF]]() : $@thin () -> ()
     // CHECK-NEXT: strong_release [[X_BOX]]#0 : $Builtin.NativeObject
+    // CHECK-NEXT: br [[EPILOG_BB]]
+    
+    // CHECK: [[EPILOG_BB]]:
     // CHECK-NOT: super_method
     // CHECK: return
     self.init(int:Int(d))