[libc] Add is_constant_evaluated type_traits (llvm#86139)

This will replace `__builtin_is_constant_evaluated` in math_extras.h.

Author: gchatelet

libc/src/__support/CPP/CMakeLists.txt

@@ -103,23 +103,24 @@ add_header_library(
   type_traits
   HDRS
     type_traits.h
-    type_traits/always_false.h
     type_traits/add_lvalue_reference.h
     type_traits/add_pointer.h
     type_traits/add_rvalue_reference.h
+    type_traits/always_false.h
     type_traits/bool_constant.h
     type_traits/conditional.h
     type_traits/decay.h
     type_traits/enable_if.h
     type_traits/false_type.h
     type_traits/integral_constant.h
-    type_traits/invoke.h
     type_traits/invoke_result.h
+    type_traits/invoke.h
     type_traits/is_arithmetic.h
     type_traits/is_array.h
     type_traits/is_base_of.h
     type_traits/is_class.h
     type_traits/is_const.h
+    type_traits/is_constant_evaluated.h
     type_traits/is_convertible.h
     type_traits/is_destructible.h
     type_traits/is_enum.h

libc/src/__support/CPP/type_traits.h

@@ -25,6 +25,7 @@
 #include "src/__support/CPP/type_traits/is_base_of.h"
 #include "src/__support/CPP/type_traits/is_class.h"
 #include "src/__support/CPP/type_traits/is_const.h"
+#include "src/__support/CPP/type_traits/is_constant_evaluated.h"
 #include "src/__support/CPP/type_traits/is_convertible.h"
 #include "src/__support/CPP/type_traits/is_destructible.h"
 #include "src/__support/CPP/type_traits/is_enum.h"

libc/src/__support/CPP/type_traits/is_constant_evaluated.h

@@ -0,0 +1,21 @@
+//===-- is_constant_evaluated type_traits -----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_LIBC_SRC___SUPPORT_CPP_TYPE_TRAITS_IS_CONSTANT_EVALUATED_H
+#define LLVM_LIBC_SRC___SUPPORT_CPP_TYPE_TRAITS_IS_CONSTANT_EVALUATED_H
+
+#include "src/__support/macros/attributes.h"
+
+namespace LIBC_NAMESPACE::cpp {
+
+LIBC_INLINE constexpr bool is_constant_evaluated() {
+  return __builtin_is_constant_evaluated();
+}
+
+} // namespace LIBC_NAMESPACE::cpp
+
+#endif // LLVM_LIBC_SRC___SUPPORT_CPP_TYPE_TRAITS_IS_CONSTANT_EVALUATED_H

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

@@ -339,6 +339,7 @@ libc_support_library(
         "src/__support/CPP/type_traits/is_base_of.h",
         "src/__support/CPP/type_traits/is_class.h",
         "src/__support/CPP/type_traits/is_const.h",
+        "src/__support/CPP/type_traits/is_constant_evaluated.h",
         "src/__support/CPP/type_traits/is_convertible.h",
         "src/__support/CPP/type_traits/is_destructible.h",
         "src/__support/CPP/type_traits/is_enum.h",
@@ -743,12 +744,12 @@ libc_support_library(
     deps = [
         ":__support_common",
         ":__support_cpp_bit",
-        ":__support_sign",
         ":__support_cpp_type_traits",
         ":__support_libc_assert",
         ":__support_macros_attributes",
         ":__support_macros_properties_types",
         ":__support_math_extras",
+        ":__support_sign",
         ":__support_uint128",
     ],
 )