Export of internal Abseil changes

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04cb3b22497190170aa5b774e98080c5de2ba60b by Abseil Team <absl-team@google.com>:

Alternative bit mixer for LowLevelHash on ARM

LowLevelHash's bit-mixer is inefficient on ARM because it calculates a 128-bit product of two 64-bit numbers. On ARM, this requires a sequence of two instructions with a high combined latency and poor throughput. This change provides alternative bit-mixing code for ARM that uses only 64-bit arithmetic (multiplication, xor, and left-shifts) and speeds things up considerably.

The bit-mixing code for ARM was inspired by by Woothash[1] and xxh3[1]. Once I landed on a sequence of operations that provided good mixing, I used a test harness to search for the combination of shift / rotate factors that provided the best mixing, as indicated by SMHasher hash quality tests. The new mixing code passes 13 out of 15 of the hash quality test suites in SMHasher, with the two failures being in the noise range: e.g. 1 collision vs. zero expected in a keyset of ~8m keys.

  [1]: https://github.com/tommyettinger/waterhash/blob/49f5cf0b63b9/woothash.h#L16-L20
  [2]: https://github.com/Cyan4973/xxHash/blob/6853ddc36e46/xxhash.h#L3240-L3265

PiperOrigin-RevId: 391833008

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17a4de1f9d623155c75b19285d414cd55a487cd6 by Saleem Abdulrasool <abdulras@google.com>:

debugging: add support for unwinding on RISCV Linux

This adds partial support for unwinding the RISCV call stack.  It is largely
duplicated from the AArch64 support with alterations for the ELF RISCV psABI.
This covers RISCV64 and RISCV32, though not the ILP32E calling convention.

PiperOrigin-RevId: 391818522

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32c93e449327b2cea32b32f6365e84b420fe1ed3 by Gennadiy Rozental <rogeeff@google.com>:

New storage for types smaller than 8 bytes.

Also adding new read interface for types smaller than or rqual to 8 bytes to avoid passing the pointer.

PiperOrigin-RevId: 391726822

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e987ac08a7787801cbfc7d7c96649e97fa8cff1a by Abseil Team <absl-team@google.com>:

Extern template `find_first_non_full` to reduce linkage size for TU with single not inlined function.

PiperOrigin-RevId: 391718862

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73af9bfcb5bf045089133e18bbd20eb5bb699172 by Gennadiy Rozental <rogeeff@google.com>:

Make most non-mutable most int128 methods and friend free functions constexpr.

Some functions are implemented offline (at least in some configurations) and can't be made constexpr. Mutable methods can't be made constexpr until we drop c++11 support.

Fixes #978

PiperOrigin-RevId: 391706535
GitOrigin-RevId: 04cb3b22497190170aa5b774e98080c5de2ba60b
Change-Id: If051fad5ff004e2e82fa53618fc04a6fe3d2d4be

2 files changed, 8 insertions, 0 deletions

diff --git a/absl/container/internal/raw_hash_set.cc b/absl/container/internal/raw_hash_set.cc
index 3c72c41a..687bcb8a 100644
--- a/absl/container/internal/raw_hash_set.cc
+++ b/absl/container/internal/raw_hash_set.cc
@@ -59,6 +59,8 @@ void ConvertDeletedToEmptyAndFullToDeleted(ctrl_t* ctrl, size_t capacity) {
   std::memcpy(ctrl + capacity + 1, ctrl, NumClonedBytes());
   ctrl[capacity] = ctrl_t::kSentinel;
 }
+// Extern template instantiotion for inline function.
+template FindInfo find_first_non_full(const ctrl_t*, size_t, size_t);
 
 }  // namespace container_internal
 ABSL_NAMESPACE_END
diff --git a/absl/container/internal/raw_hash_set.h b/absl/container/internal/raw_hash_set.h
index ade2f584..18b1f5a4 100644
--- a/absl/container/internal/raw_hash_set.h
+++ b/absl/container/internal/raw_hash_set.h
@@ -570,6 +570,7 @@ inline probe_seq<Group::kWidth> probe(const ctrl_t* ctrl, size_t hash,
 // - the input is already a set
 // - there are enough slots
 // - the element with the hash is not in the table
+template <typename = void>
 inline FindInfo find_first_non_full(const ctrl_t* ctrl, size_t hash,
                                     size_t capacity) {
   auto seq = probe(ctrl, hash, capacity);
@@ -593,6 +594,11 @@ inline FindInfo find_first_non_full(const ctrl_t* ctrl, size_t hash,
   }
 }
 
+// Extern template for inline function keep possibility of inlining.
+// When compiler decided to not inline, no symbols will be added to the
+// corresponding translation unit.
+extern template FindInfo find_first_non_full(const ctrl_t*, size_t, size_t);
+
 // Reset all ctrl bytes back to ctrl_t::kEmpty, except the sentinel.
 inline void ResetCtrl(size_t capacity, ctrl_t* ctrl, const void* slot,
                       size_t slot_size) {