Move down_cast to platform/casts.h

PiperOrigin-RevId: 289736444
Change-Id: I93321c9130243b15d789bd4ec63588d54adc011e

tensorflow/core/BUILD

@@ -1974,6 +1974,7 @@ cc_library(
         "//tensorflow/core/platform:abi",
         "//tensorflow/core/platform:base64",
         "//tensorflow/core/platform:blocking_counter",
+        "//tensorflow/core/platform:casts",
         "//tensorflow/core/platform:coding",
         "//tensorflow/core/platform:context",
         "//tensorflow/core/platform:cord",

tensorflow/core/kernels/data/iterator_ops.cc

@@ -43,6 +43,7 @@ limitations under the License.
 #include "tensorflow/core/lib/random/random.h"
 #include "tensorflow/core/lib/strings/strcat.h"
 #include "tensorflow/core/lib/strings/stringprintf.h"
+#include "tensorflow/core/platform/casts.h"
 #include "tensorflow/core/platform/env.h"
 #include "tensorflow/core/platform/mutex.h"
 #include "tensorflow/core/platform/refcount.h"

tensorflow/core/kernels/data/iterator_ops.h

@@ -124,20 +124,6 @@ class IteratorHandleOp : public OpKernel {
   // inconsistent capacities.
   Status VerifyResource(IteratorResource* resource);
 
-  template <typename To, typename From>  // use like this: down_cast<T*>(foo);
-  static inline To down_cast(From* f) {  // so we only accept pointers
-    static_assert(
-        (std::is_base_of<From, typename std::remove_pointer<To>::type>::value),
-        "target type not derived from source type");
-
-    // We skip the assert and hence the dynamic_cast if RTTI is disabled.
-#if !defined(__GNUC__) || defined(__GXX_RTTI)
-    // Uses RTTI in dbg and fastbuild. asserts are disabled in opt builds.
-    assert(f == nullptr || dynamic_cast<To>(f) != nullptr);
-#endif  // !defined(__GNUC__) || defined(__GXX_RTTI)
-    return static_cast<To>(f);
-  }
-
   FunctionLibraryRuntime* CreatePrivateFLR(
       OpKernelContext* ctx, std::unique_ptr<DeviceMgr>* device_mgr,
       std::unique_ptr<FunctionLibraryDefinition>* flib_def,

tensorflow/core/kernels/functional_ops.cc

@@ -25,6 +25,7 @@ limitations under the License.
 #include "tensorflow/core/framework/tensor_shape.h"
 #include "tensorflow/core/lib/core/errors.h"
 #include "tensorflow/core/lib/core/threadpool.h"
+#include "tensorflow/core/platform/casts.h"
 #include "tensorflow/core/profiler/lib/traceme.h"
 
 namespace tensorflow {
@@ -41,21 +42,6 @@ Status Instantiate(FunctionLibraryRuntime* lib, const NameAttrList& func,
   return lib->Instantiate(func.name(), AttrSlice(&func.attr()), handle);
 }
 
-template <typename To, typename From>  // use like this: down_cast<T*>(foo);
-inline To down_cast(From* f) {         // so we only accept pointers
-  static_assert(
-      (std::is_base_of<From, typename std::remove_pointer<To>::type>::value),
-      "target type not derived from source type");
-
-  // We skip the assert and hence the dynamic_cast if RTTI is disabled.
-#if !defined(__GNUC__) || defined(__GXX_RTTI)
-  // Uses RTTI in dbg and fastbuild. asserts are disabled in opt builds.
-  assert(f == nullptr || dynamic_cast<To>(f) != nullptr);
-#endif  // !defined(__GNUC__) || defined(__GXX_RTTI)
-
-  return static_cast<To>(f);
-}
-
 // If "t" is a scalar of a supported type, returns t != 0 in "*v".
 Status ToBool(gtl::ArraySlice<Tensor> t, bool* v) {
   if (t.size() != 1) {

tensorflow/core/kernels/resource_variable_ops.cc

@@ -73,6 +73,7 @@ limitations under the License.
 #include "tensorflow/core/kernels/variable_ops.h"
 #include "tensorflow/core/lib/core/errors.h"
 #include "tensorflow/core/lib/core/refcount.h"
+#include "tensorflow/core/platform/casts.h"
 #include "tensorflow/core/platform/mem.h"
 #include "tensorflow/core/platform/mutex.h"
 #include "tensorflow/core/platform/types.h"
@@ -104,7 +105,7 @@ Status CopyVariable(int output_idx, OpKernelContext* ctx, const Tensor* t) {
   } else if (ctx->op_device_context() != nullptr) {
     // TODO(apassos): remove the down_cast by just returning Device* from
     // OpKernelContext
-    Device* device = static_cast<Device*>(ctx->device());
+    Device* device = down_cast<Device*>(ctx->device());
     ctx->op_device_context()->CopyTensorInSameDevice(
         t, device, output, [&n, &status](const Status& s) {
           status = s;

tensorflow/core/platform/BUILD

@@ -158,6 +158,14 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "casts",
+    hdrs = ["casts.h"],
+    deps = [
+        ":platform",
+    ] + tf_platform_deps("casts"),
+)
+
 cc_library(
     name = "cuda",
     hdrs = ["cuda.h"],
@@ -1060,6 +1068,7 @@ filegroup(
     name = "lib_hdrs",
     srcs = [
         "abi.h",
+        "casts.h",
         "context.h",
         "cpu_feature_guard.h",
         "cpu_info.h",
@@ -1254,6 +1263,7 @@ filegroup(
         "//tensorflow/core/platform:base64.h",
         "//tensorflow/core/platform:blocking_counter.h",
         "//tensorflow/core/platform:byte_order.h",
+        "//tensorflow/core/platform:casts.h",
         "//tensorflow/core/platform:coding.cc",
         "//tensorflow/core/platform:coding.h",
         "//tensorflow/core/platform:context.h",
@@ -1360,6 +1370,7 @@ filegroup(
     name = "legacy_srcs_no_runtime",
     srcs = [
         ":legacy_srcs_common",
+        "//tensorflow/core/platform/default:casts.h",
         "//tensorflow/core/platform/default:context.h",
         "//tensorflow/core/platform/default:cord.h",
         "//tensorflow/core/platform/default:dynamic_annotations.h",

tensorflow/core/platform/casts.h

@@ -0,0 +1,31 @@
+/* Copyright 2020 The TensorFlow Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+
+#ifndef TENSORFLOW_CORE_PLATFORM_CASTS_H_
+#define TENSORFLOW_CORE_PLATFORM_CASTS_H_
+
+#include "tensorflow/core/platform/platform.h"
+
+#if defined(PLATFORM_GOOGLE)
+#include "tensorflow/core/platform/google/casts.h"
+#elif defined(PLATFORM_POSIX) || defined(PLATFORM_POSIX_ANDROID) ||    \
+    defined(PLATFORM_GOOGLE_ANDROID) || defined(PLATFORM_POSIX_IOS) || \
+    defined(PLATFORM_GOOGLE_IOS) || defined(PLATFORM_WINDOWS)
+#include "tensorflow/core/platform/default/casts.h"
+#else
+#error Define the appropriate PLATFORM_<foo> macro for this platform
+#endif
+
+#endif  // TENSORFLOW_CORE_PLATFORM_CASTS_H_

tensorflow/core/platform/default/BUILD

@@ -9,6 +9,16 @@ package(
     licenses = ["notice"],  # Apache 2.0
 )
 
+cc_library(
+    name = "casts",
+    hdrs = ["casts.h"],
+    tags = [
+        "manual",
+        "no_oss",
+        "nobuilder",
+    ],
+)
+
 cc_library(
     name = "context",
     hdrs = ["//tensorflow/core/platform:context.h"],

tensorflow/core/platform/default/build_config.bzl

@@ -541,6 +541,7 @@ def tf_proto_library(
 
 def tf_additional_lib_hdrs():
     return [
+        "//tensorflow/core/platform/default:casts.h",
         "//tensorflow/core/platform/default:context.h",
         "//tensorflow/core/platform/default:cord.h",
         "//tensorflow/core/platform/default:dynamic_annotations.h",

tensorflow/core/platform/default/casts.h

@@ -0,0 +1,92 @@
+/* Copyright 2020 The TensorFlow Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+
+#ifndef TENSORFLOW_CORE_PLATFORM_DEFAULT_CASTS_H_
+#define TENSORFLOW_CORE_PLATFORM_DEFAULT_CASTS_H_
+
+#include <assert.h>  // for use with down_cast<>
+
+#include <type_traits>
+
+namespace tensorflow {
+
+// An "upcast", i.e. a conversion from a pointer to an object to a pointer to a
+// base subobject, always succeeds if the base is unambiguous and accessible,
+// and so it's fine to use implicit_cast.
+//
+// A "downcast", i.e. a conversion from a pointer to an object to a pointer
+// to a more-derived object that may contain the original object as a base
+// subobject, cannot safely be done using static_cast, because you do not
+// generally know whether the source object is really the base subobject of
+// a containing, more-derived object of the target type. Thus, when you
+// downcast in a polymorphic type hierarchy, you should use the following
+// function template.
+//
+// In debug mode, we use dynamic_cast to double-check whether the downcast is
+// legal (we die if it's not). In normal mode, we do the efficient static_cast
+// instead. Thus, it's important to test in debug mode to make sure the cast is
+// legal!
+//
+// This is the only place in the codebase we should use dynamic_cast.
+// In particular, you should NOT use dynamic_cast for RTTI, e.g. for
+// code like this:
+//    if (auto* p = dynamic_cast<Subclass1*>(foo)) HandleASubclass1Object(p);
+//    if (auto* p = dynamic_cast<Subclass2*>(foo)) HandleASubclass2Object(p);
+// You should design the code some other way not to need this.
+
+template <typename To, typename From>  // use like this: down_cast<T*>(foo);
+inline To down_cast(From* f) {         // so we only accept pointers
+  static_assert(
+      (std::is_base_of<From, typename std::remove_pointer<To>::type>::value),
+      "target type not derived from source type");
+
+  // We skip the assert and hence the dynamic_cast if RTTI is disabled.
+#if !defined(__GNUC__) || defined(__GXX_RTTI)
+  // Uses RTTI in dbg and fastbuild. asserts are disabled in opt builds.
+  assert(f == nullptr || dynamic_cast<To>(f) != nullptr);
+#endif  // !defined(__GNUC__) || defined(__GXX_RTTI)
+
+  return static_cast<To>(f);
+}
+
+// Overload of down_cast for references. Use like this: down_cast<T&>(foo).
+// The code is slightly convoluted because we're still using the pointer
+// form of dynamic cast. (The reference form throws an exception if it
+// fails.)
+//
+// There's no need for a special const overload either for the pointer
+// or the reference form. If you call down_cast with a const T&, the
+// compiler will just bind From to const T.
+template <typename To, typename From>
+inline To down_cast(From& f) {
+  static_assert(std::is_lvalue_reference<To>::value,
+                "target type not a reference");
+  static_assert(
+      (std::is_base_of<From, typename std::remove_reference<To>::type>::value),
+      "target type not derived from source type");
+
+  // We skip the assert and hence the dynamic_cast if RTTI is disabled.
+#if !defined(__GNUC__) || defined(__GXX_RTTI)
+  // RTTI: debug mode only
+  assert(dynamic_cast<typename std::remove_reference<To>::type*>(&f) !=
+         nullptr);
+#endif  // !defined(__GNUC__) || defined(__GXX_RTTI)
+
+  return static_cast<To>(f);
+}
+
+}  // namespace tensorflow
+
+#endif  // TENSORFLOW_CORE_PLATFORM_DEFAULT_CASTS_H_