[libc] Added checks to src and dest types in bit_cast

This patch adds assertions to prevent the compilation when we try to
bit cast a type that is not trivially copyable when using
__builtin_bit_cast, or when we try to bit cast a type that is not
trivially copyable and trivially constructable when using memcpy.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D148739

diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index 37248c77fe9d7bb79805b54c386743a58d2385b8..4241f2b52b543cf6430342f87c75851cf7fa7ae2 100644 (file)
--- a/libc/src/__support/CPP/bit.h
+++ b/libc/src/__support/CPP/bit.h
@@ -9,6 +9,7 @@
 #ifndef LLVM_LIBC_SUPPORT_CPP_BIT_H
 #define LLVM_LIBC_SUPPORT_CPP_BIT_H
 
+#include "src/__support/CPP/type_traits.h"
 #include "src/__support/macros/config.h" // LIBC_HAS_BUILTIN
 
 namespace __llvm_libc::cpp {
@@ -25,9 +26,15 @@ namespace __llvm_libc::cpp {
 // GCC >= 8 and Clang >= 6.
 template <class To, class From> constexpr To bit_cast(const From &from) {
   static_assert(sizeof(To) == sizeof(From), "To and From must be of same size");
+  static_assert(cpp::is_trivially_copyable<To>::value &&
+                    cpp::is_trivially_copyable<From>::value,
+                "Cannot bit-cast instances of non-trivially copyable classes.");
 #if defined(LLVM_LIBC_HAS_BUILTIN_BIT_CAST)
   return __builtin_bit_cast(To, from);
 #else
+  static_assert(cpp::is_trivially_constructible<To>::value,
+                "This implementation additionally requires destination type to "
+                "be trivially constructible");
   To to;
   char *dst = reinterpret_cast<char *>(&to);
   const char *src = reinterpret_cast<const char *>(&from);

diff --git a/libc/src/__support/CPP/type_traits.h b/libc/src/__support/CPP/type_traits.h
index 7457bbefed67bc38b7c409c967f4fd3aee81c3c9..e5614021ca17aa54a296399cee6a986308c749c7 100644 (file)
--- a/libc/src/__support/CPP/type_traits.h
+++ b/libc/src/__support/CPP/type_traits.h
@@ -12,9 +12,7 @@
 namespace __llvm_libc {
 namespace cpp {
 
-template <typename T> struct type_identity {
-  using type = T;
-};
+template <typename T> struct type_identity { using type = T; };
 
 template <bool B, typename T> struct enable_if;
 template <typename T> struct enable_if<true, T> : type_identity<T> {};
@@ -28,6 +26,14 @@ template <typename T, T v> struct integral_constant {
 using true_type = cpp::integral_constant<bool, true>;
 using false_type = cpp::integral_constant<bool, false>;
 
+template <class T>
+struct is_trivially_copyable
+    : public integral_constant<bool, __is_trivially_copyable(T)> {};
+
+template <class T, class... Args>
+struct is_trivially_constructible
+    : integral_constant<bool, __is_trivially_constructible(T, Args...)> {};
+
 template <typename T, typename U> struct is_same : cpp::false_type {};
 template <typename T> struct is_same<T, T> : cpp::true_type {};
 template <typename T, typename U>