Export of internal Abseil changes

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7f5caec21a1a88db6486b8bc2e5f6d5baba076ed by Derek Mauro <dmauro@google.com>:

Tag absl::StatusOr with [[nodiscard]] when it is available

[[nodiscard]] provides better diagnostics on classes than the current
ABSL_MUST_USE_RESULT, which expands to
__attribute__((warn_unused_result))

Ideally we would make ABSL_MUST_USE_RESULT expand to [[nodiscard]], but
we would need to fix all code to build with [[nodiscard]] first.

PiperOrigin-RevId: 422628161

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236be69f0f34ccaa3adc831075613847797e6557 by Jorg Brown <jorg@google.com>:

Make sure all of absl/strings compiles even with -Wsign-compare and -Wconversion warnings.

PiperOrigin-RevId: 422573904

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005669883a8794e6d19dc4bbb4f0e18032e2fbc9 by Chris Kennelly <ckennelly@google.com>:

Include sampling stride in hashtable sampling data.

This allows us to weight each sample to control for our sampling rate.

PiperOrigin-RevId: 421886935

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78046ce6b429b9f5b6c97b05e8448a791db93bbe by Abseil Team <absl-team@google.com>:

Use __builtin_bit_cast for absl::bit_cast when possible

This makes absl::bit_cast match the requirements of the standard when compiler support exists.

PiperOrigin-RevId: 421883999

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f397461f4bbeabd32437df0f2275663aeb51adb2 by Derek Mauro <dmauro@google.com>:

Tag absl::Status with [[nodiscard]] when it is available

[[nodiscard]] provides better diagnostics on classes than the current
ABSL_MUST_USE_RESULT, which expands to
__attribute__((warn_unused_result))

Ideally we would make ABSL_MUST_USE_RESULT expand to [[nodiscard]], but
we would need to fix all code to build with [[nodiscard]] first.

PiperOrigin-RevId: 421825565
GitOrigin-RevId: 7f5caec21a1a88db6486b8bc2e5f6d5baba076ed
Change-Id: I760b45b68f6012809c70c2a584e4144a99f98733

1 files changed, 14 insertions, 4 deletions

diff --git a/absl/base/casts.h b/absl/base/casts.h
index b16af233..bf100efa 100644
--- a/absl/base/casts.h
+++ b/absl/base/casts.h
@@ -44,8 +44,12 @@ struct is_bitcastable
           bool,
           sizeof(Dest) == sizeof(Source) &&
               type_traits_internal::is_trivially_copyable<Source>::value &&
-              type_traits_internal::is_trivially_copyable<Dest>::value &&
-              std::is_default_constructible<Dest>::value> {};
+              type_traits_internal::is_trivially_copyable<Dest>::value
+#if !ABSL_HAVE_BUILTIN(__builtin_bit_cast)
+              && std::is_default_constructible<Dest>::value
+#endif
+          > {
+};
 
 }  // namespace internal_casts
 
@@ -147,20 +151,26 @@ constexpr To implicit_cast(typename absl::internal::identity_t<To> to) {
 // introducing this undefined behavior (since the original value is never
 // accessed in the wrong way).
 //
-// NOTE: The requirements here are stricter than the bit_cast of standard
-// proposal P0476 due to the need for workarounds and lack of intrinsics.
+// NOTE: The requirements here are more strict than the bit_cast of standard
+// proposal P0476 when __builtin_bit_cast is not available.
 // Specifically, this implementation also requires `Dest` to be
 // default-constructible.
 template <
     typename Dest, typename Source,
     typename std::enable_if<internal_casts::is_bitcastable<Dest, Source>::value,
                             int>::type = 0>
+#if ABSL_HAVE_BUILTIN(__builtin_bit_cast)
+inline constexpr Dest bit_cast(const Source& source) {
+  return __builtin_bit_cast(Dest, source);
+}
+#else
 inline Dest bit_cast(const Source& source) {
   Dest dest;
   memcpy(static_cast<void*>(std::addressof(dest)),
          static_cast<const void*>(std::addressof(source)), sizeof(dest));
   return dest;
 }
+#endif
 
 // NOTE: This overload is only picked if the requirements of bit_cast are
 // not met. It is therefore UB, but is provided temporarily as previous