[IRGen] [Builtin] Update zeroInitializer to support addresses.

Adds support for addresses in `Builtin.zeroInitializer`. If an address is passed as the first (and only) argument, it will be zero'd out with a memset.

This will "fix" the C++ default constructor for address types.

Author: zoecarver

lib/IRGen/GenBuiltin.cpp

@@ -980,9 +980,21 @@ if (Builtin.ID == BuiltinValueKind::id) { \
   }
 
   if (Builtin.ID == BuiltinValueKind::ZeroInitializer) {
-    // Build a zero initializer of the result type.
-    auto valueTy = getLoweredTypeAndTypeInfo(IGF.IGM,
-                                             substitutions.getReplacementTypes()[0]);
+    auto genericArg = substitutions.getReplacementTypes()[0];
+    auto valueTy = getLoweredTypeAndTypeInfo(IGF.IGM, genericArg);
+    // If the builtin returns void (and the generic argument isn't void), this
+    // is an address.
+    if (resultType.isVoid() && !genericArg->isVoid()) {
+      // The first (and only) argument will be a pointer. All we need to do is
+      // null it out.
+      IGF.Builder.CreateMemSet(
+          args.claimNext(), llvm::ConstantInt::get(IGF.IGM.Int8Ty, 0),
+          valueTy.second.getSize(IGF, valueTy.first),
+          llvm::MaybeAlign(valueTy.second.getBestKnownAlignment()));
+      return;
+    }
+
+    // Otherwise, build a zero initializer of the result type.
     auto schema = valueTy.second.getSchema();
     for (auto &elt : schema) {
       out.add(llvm::Constant::getNullValue(elt.getScalarType()));

test/IRGen/builtin-zero-initializer-address.sil

@@ -0,0 +1,58 @@
+// RUN: %swift -module-name main %s -emit-ir | %FileCheck %s
+
+import Builtin
+
+// CHECK-LABEL: define swiftcc void @test_trivial_type
+// CHECK: [[I32PTR:%.*]] = alloca i32, align 4
+// CHECK: [[I8PTR:%.*]] = bitcast i32* [[I32PTR]] to i8*
+// CHECK: call void @llvm.lifetime.start.p0i8(i64 4, i8* [[I8PTR]])
+// CHECK: [[I8PTR2:%.*]] = bitcast i32* [[I32PTR]] to i8*
+// CHECK: call void @llvm.memset.p0i8.i64(i8* align 4 [[I8PTR2]], i8 0, i64 4, i1 false)
+// CHECK: ret void
+sil @test_trivial_type : $@convention(thin) () -> () {
+bb0:
+  %0 = alloc_stack $Builtin.Int32
+  %1 = builtin "zeroInitializer"<Builtin.Int32>(%0 : $*Builtin.Int32) : $()
+  dealloc_stack %0 : $*Builtin.Int32
+  %t = tuple ()
+  return %t : $()
+}
+
+// CHECK-LABEL: define swiftcc void @test_object_type
+// CHECK: [[PTR:%.*]] = alloca %AnyObject, align 8
+// CHECK: [[I8PTR:%.*]] = bitcast %AnyObject* [[PTR]] to i8*
+// CHECK: call void @llvm.lifetime.start.p0i8(i64 8, i8* [[I8PTR]])
+// CHECK: [[I8PTR2:%.*]] = bitcast %AnyObject* [[PTR]] to i8*
+// CHECK: call void @llvm.memset.p0i8.i64(i8* align 8 [[I8PTR2]], i8 0, i64 8, i1 false)
+// CHECK: ret void
+sil @test_object_type : $@convention(thin) () -> () {
+bb0:
+  %0 = alloc_stack $Builtin.AnyObject
+  %1 = builtin "zeroInitializer"<Builtin.AnyObject>(%0 : $*Builtin.AnyObject) : $()
+  dealloc_stack %0 : $*Builtin.AnyObject
+  %t = tuple ()
+  return %t : $()
+}
+
+// CHECK_LABEL: define swiftcc void @test_generic (%swift.type* %0, %swift.type* %T)
+// CHECK: [[TYPE_PTR:%.*]] = bitcast %swift.type* %T to i8***
+// CHECK: [[WITNESS_PTR:%.*]] = getelementptr inbounds i8**, i8*** [[TYPE_PTR:%.*]], i64 -1
+// CHECK: [[T_WITNESS:%.*]] = load i8**, i8*** [[WITNESS_PTR]]
+// CHECK: [[WITNESS:%.*]] = bitcast i8** [[T_WITNESS]] to %swift.vwtable*
+// CHECK: [[SIZE_PTR:%.*]] = getelementptr inbounds %swift.vwtable, %swift.vwtable* [[WITNESS]], i32 0, i32 8
+// CHECK: [[SIZE:%.*]] = load i64, i64* [[SIZE_PTR]]
+// CHECK: [[SIZE_TMP:%.*]] = alloca i8, i64 %size
+// CHECK: call void @llvm.lifetime.start.p0i8(i64 -1, i8* [[SIZE_TMP]])
+// CHECK: [[OBJECT_PTR:%.*]] = bitcast i8* [[SIZE_TMP]] to %swift.opaque*
+// CHECK: [[OBJECT_RAW_PTR:%.*]] = bitcast %swift.opaque* [[OBJECT_PTR]] to i8*
+// CHECK: call void @llvm.memset.p0i8.i64(i8* align 1 [[OBJECT_RAW_PTR]], i8 0, i64 [[SIZE]], i1 false)
+// CHECK: ret void
+sil @test_generic : $@convention(thin) <T> (@thick T.Type) -> () {
+bb0(%0 : $@thick T.Type):
+  %1 = alloc_stack $T
+  %2 = builtin "zeroInitializer"<T>(%1 : $*T) : $()
+  destroy_addr %1 : $*T
+  dealloc_stack %1 : $*T
+  %t = tuple ()
+  return %t : $()
+}