Change the macro ABSL_IS_TRIVIALLY_RELOCATABLE into a type trait - absl::is_trivially_relocatable - and move it from optimization.h to type_traits.h.

Example of how to change to the new type trait:
```
#include "absl/base/attributes.h"

if (ABSL_IS_TRIVIALLY_RELOCATABLE(T)) { DoSomething(); }
```
to
```
#include "absl/meta/type_traits.h"

if (absl::is_trivially_relocatable<T>::value) { DoSomething(); }
```

Note that optimization.h is also built in C mode so we can't put a type trait there.

PiperOrigin-RevId: 475633715
Change-Id: I2bc85f3f6711d1280049fd01eb97c497d2d0d929

absl/base/optimization.h

@@ -249,28 +249,4 @@
 #define ABSL_INTERNAL_UNIQUE_SMALL_NAME()
 #endif
 
-// ABSL_IS_TRIVIALLY_RELOCATABLE(type)
-// Detects whether a type is "trivially relocatable" -- meaning it can be
-// relocated without invoking the constructor/destructor, using a form of move
-// elision.
-//
-// Example:
-//
-// if constexpr (ABSL_IS_TRIVIALLY_RELOCATABLE(T)) {
-//   memcpy(new_location, old_location, sizeof(T));
-// } else {
-//   new(new_location) T(std::move(*old_location));
-//   old_location->~T();
-// }
-//
-// Upstream documentation:
-//
-// https://clang.llvm.org/docs/LanguageExtensions.html#:~:text=__is_trivially_relocatable
-//
-#if ABSL_HAVE_BUILTIN(__is_trivially_relocatable)
-#define ABSL_IS_TRIVIALLY_RELOCATABLE(type) __is_trivially_relocatable(type)
-#else
-#define ABSL_IS_TRIVIALLY_RELOCATABLE(type) false
-#endif
-
 #endif  // ABSL_BASE_OPTIMIZATION_H_

absl/base/optimization_test.cc

@@ -15,7 +15,6 @@
 #include "absl/base/optimization.h"
 
 #include "gtest/gtest.h"
-#include "absl/base/attributes.h"
 #include "absl/types/optional.h"
 
 namespace {
@@ -127,22 +126,4 @@ TEST(PredictTest, ExplicitBoolConversion) {
   if (ABSL_PREDICT_FALSE(is_false)) ADD_FAILURE();
 }
 
-TEST(TrivallyRelocatable, Sanity) {
-#if !defined(ABSL_HAVE_ATTRIBUTE_TRIVIAL_ABI) || \
-    !ABSL_HAVE_BUILTIN(__is_trivially_relocatable)
-  GTEST_SKIP() << "No trivial ABI support.";
-#endif
-
-  struct Trivial {};
-  struct NonTrivial {
-    NonTrivial(const NonTrivial&) {}
-  };
-  struct ABSL_ATTRIBUTE_TRIVIAL_ABI TrivialAbi {
-    TrivialAbi(const TrivialAbi&) {}
-  };
-  EXPECT_TRUE(ABSL_IS_TRIVIALLY_RELOCATABLE(Trivial));
-  EXPECT_FALSE(ABSL_IS_TRIVIALLY_RELOCATABLE(NonTrivial));
-  EXPECT_TRUE(ABSL_IS_TRIVIALLY_RELOCATABLE(TrivialAbi));
-}
-
 }  // namespace

absl/meta/BUILD.bazel

@@ -42,6 +42,7 @@ cc_test(
     linkopts = ABSL_DEFAULT_LINKOPTS,
     deps = [
         ":type_traits",
+        "//absl/base:core_headers",
         "@com_google_googletest//:gtest_main",
     ],
 )

absl/meta/CMakeLists.txt

@@ -34,6 +34,7 @@ absl_cc_test(
   COPTS
     ${ABSL_TEST_COPTS}
   DEPS
+    absl::core_headers
     absl::type_traits
     GTest::gmock_main
 )

absl/meta/type_traits.h

@@ -813,6 +813,34 @@ using swap_internal::Swap;
 using swap_internal::StdSwapIsUnconstrained;
 
 }  // namespace type_traits_internal
+
+// absl::is_trivially_relocatable<T>
+// Detects whether a type is "trivially relocatable" -- meaning it can be
+// relocated without invoking the constructor/destructor, using a form of move
+// elision.
+//
+// Example:
+//
+// if constexpr (absl::is_trivially_relocatable<T>::value) {
+//   memcpy(new_location, old_location, sizeof(T));
+// } else {
+//   new(new_location) T(std::move(*old_location));
+//   old_location->~T();
+// }
+//
+// Upstream documentation:
+//
+// https://clang.llvm.org/docs/LanguageExtensions.html#:~:text=__is_trivially_relocatable
+//
+#if ABSL_HAVE_BUILTIN(__is_trivially_relocatable)
+template <class T>
+struct is_trivially_relocatable
+    : std::integral_constant<bool, __is_trivially_relocatable(T)> {};
+#else
+template <class T>
+struct is_trivially_relocatable : std::integral_constant<bool, false> {};
+#endif
+
 ABSL_NAMESPACE_END
 }  // namespace absl
 

absl/meta/type_traits_test.cc

@@ -21,6 +21,7 @@
 #include <vector>
 
 #include "gtest/gtest.h"
+#include "absl/base/attributes.h"
 
 namespace {
 
@@ -1394,4 +1395,22 @@ TEST(TypeTraitsTest, IsNothrowSwappable) {
   EXPECT_TRUE(IsNothrowSwappable<adl_namespace::SpecialNoexceptSwap>::value);
 }
 
+TEST(TrivallyRelocatable, Sanity) {
+#if !defined(ABSL_HAVE_ATTRIBUTE_TRIVIAL_ABI) || \
+    !ABSL_HAVE_BUILTIN(__is_trivially_relocatable)
+  GTEST_SKIP() << "No trivial ABI support.";
+#endif
+
+  struct Trivial {};
+  struct NonTrivial {
+    NonTrivial(const NonTrivial&) {}  // NOLINT
+  };
+  struct ABSL_ATTRIBUTE_TRIVIAL_ABI TrivialAbi {
+    TrivialAbi(const TrivialAbi&) {}  // NOLINT
+  };
+  EXPECT_TRUE(absl::is_trivially_relocatable<Trivial>::value);
+  EXPECT_FALSE(absl::is_trivially_relocatable<NonTrivial>::value);
+  EXPECT_TRUE(absl::is_trivially_relocatable<TrivialAbi>::value);
+}
+
 }  // namespace