[PATCH] D142305: [ADT] llvm::bit_cast - use __builtin_bit_cast if available

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: kazu, dblaikie, MaskRay, barannikov88.
Herald added a project: All.
RKSimon requested review of this revision.
Herald added a project: LLVM.

If the compiler supports __builtin_bit_cast we should try to use it instead of std::memcpy (and avoid including the cstring header).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D142305

Files:
  llvm/include/llvm/ADT/bit.h


Index: llvm/include/llvm/ADT/bit.h
===================================================================
--- llvm/include/llvm/ADT/bit.h
+++ llvm/include/llvm/ADT/bit.h
@@ -16,10 +16,13 @@
 
 #include "llvm/Support/Compiler.h"
 #include <cstdint>
-#include <cstring>
 #include <limits>
 #include <type_traits>
 
+#if !__has_builtin(__builtin_bit_cast)
+#include <cstring>
+#endif
+
 #ifdef _MSC_VER
 // Declare these intrinsics manually rather including intrin.h. It's very
 // expensive, and bit.h is popular via MathExtras.h.
@@ -44,9 +47,13 @@
     typename = std::enable_if_t<std::is_trivially_copyable<To>::value>,
     typename = std::enable_if_t<std::is_trivially_copyable<From>::value>>
 [[nodiscard]] inline To bit_cast(const From &from) noexcept {
+#if __has_builtin(__builtin_bit_cast)
+  return __builtin_bit_cast(To, from);
+#else
   To to;
   std::memcpy(&to, &from, sizeof(To));
   return to;
+#endif
 }
 
 template <typename T, typename = std::enable_if_t<std::is_unsigned_v<T>>>


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