[libc-commits] [PATCH] D148739: [libc] Use __builtin_bit_cast only when src and dest types are trivially copyable
Mikhail Ramalho via Phabricator via libc-commits
libc-commits at lists.llvm.org
Wed Apr 19 16:25:15 PDT 2023
mikhail.ramalho updated this revision to Diff 515125.
mikhail.ramalho added a comment.
Remove C++ standard library in the runtime components of the libc
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D148739/new/
https://reviews.llvm.org/D148739
Files:
libc/src/__support/CPP/bit.h
libc/src/__support/CPP/type_traits.h
Index: libc/src/__support/CPP/type_traits.h
===================================================================
--- libc/src/__support/CPP/type_traits.h
+++ libc/src/__support/CPP/type_traits.h
@@ -28,6 +28,10 @@
using true_type = cpp::integral_constant<bool, true>;
using false_type = cpp::integral_constant<bool, false>;
+template <class _Tp>
+struct is_trivially_copyable
+ : public integral_constant<bool, __is_trivially_copyable(_Tp)> {};
+
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>
Index: libc/src/__support/CPP/bit.h
===================================================================
--- libc/src/__support/CPP/bit.h
+++ 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 {
@@ -26,8 +27,10 @@
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");
#if defined(LLVM_LIBC_HAS_BUILTIN_BIT_CAST)
- return __builtin_bit_cast(To, from);
-#else
+ if constexpr (cpp::is_trivially_copyable<To>::value &&
+ cpp::is_trivially_copyable<From>::value)
+ return __builtin_bit_cast(To, from);
+#endif // defined(LLVM_LIBC_HAS_BUILTIN_BIT_CAST)
To to;
char *dst = reinterpret_cast<char *>(&to);
const char *src = reinterpret_cast<const char *>(&from);
@@ -38,7 +41,6 @@
dst[i] = src[i];
#endif // defined(LLVM_LIBC_HAS_BUILTIN_MEMCPY_INLINE)
return to;
-#endif // defined(LLVM_LIBC_HAS_BUILTIN_BIT_CAST)
}
} // namespace __llvm_libc::cpp
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