Export of internal Abseil changes.

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6258612abc571fa7f51f34046b410c73486505fe by Derek Mauro <dmauro@google.com>:

Rollback checking the return value of pthread functions in thread_identity.cc.

PiperOrigin-RevId: 248381230

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fda6acddab04fc53eeb84ec253de4a9655bf9a36 by CJ Johnson <johnsoncj@google.com>:

Removes too-restrictive benchmark abstraction in inlined_vector_benchmark

PiperOrigin-RevId: 248366325

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68674991e63c919de8a3eebced5adec6466ec8fe by Abseil Team <absl-team@google.com>:

Check for pthread_setmask() failure.

Log a fatal error message if pthread_setmask() fails.

PiperOrigin-RevId: 248347115

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45389e44c0d1badafb6b560cae3df99fc8bd16ac by Derek Mauro <dmauro@google.com>:

Fix a -Wredundant-move warning in GCC 9.

PiperOrigin-RevId: 248338682

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12cfbacf599084a8ac6bf4395026cbf193c85a26 by Derek Mauro <dmauro@google.com>:

Check the return value of pthread functions in thread_identity.cc.

PiperOrigin-RevId: 248327118

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2bc69998e68cfee96e812ce800e83cce7a715091 by Benjamin Barenblat <bbaren@google.com>:

Encourage judicious use of ABSL_PREDICT_{TRUE,FALSE}

Recommend that users use branch prediction annotations only on hot,
consistently mispredicted branches.

PiperOrigin-RevId: 248222450
GitOrigin-RevId: 6258612abc571fa7f51f34046b410c73486505fe
Change-Id: I09d409f9a3941ee926b8476b5473f9c4899cc3ff

4 files changed, 19 insertions, 11 deletions

diff --git a/absl/base/internal/low_level_alloc.cc b/absl/base/internal/low_level_alloc.cc
index 5a8199e6..36e4f1ba 100644
--- a/absl/base/internal/low_level_alloc.cc
+++ b/absl/base/internal/low_level_alloc.cc
@@ -294,7 +294,10 @@ class SCOPED_LOCKABLE ArenaLock {
     arena_->mu.Unlock();
 #ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
     if (mask_valid_) {
-      pthread_sigmask(SIG_SETMASK, &mask_, nullptr);
+      const int err = pthread_sigmask(SIG_SETMASK, &mask_, nullptr);
+      if (err != 0) {
+        ABSL_RAW_LOG(FATAL, "pthread_sigmask failed: %d", err);
+      }
     }
 #endif
     left_ = true;
diff --git a/absl/base/optimization.h b/absl/base/optimization.h
index 6974f1f6..0dcbef32 100644
--- a/absl/base/optimization.h
+++ b/absl/base/optimization.h
@@ -163,6 +163,12 @@
 // Compilers can use the information that a certain branch is not likely to be
 // taken (for instance, a CHECK failure) to optimize for the common case in
 // the absence of better information (ie. compiling gcc with `-fprofile-arcs`).
+//
+// Recommendation: Modern CPUs dynamically predict branch execution paths,
+// typically with accuracy greater than 97%. As a result, annotating every
+// branch in a codebase is likely counterproductive; however, annotating
+// specific branches that are both hot and consistently mispredicted is likely
+// to yield performance improvements.
 #if ABSL_HAVE_BUILTIN(__builtin_expect) || \
     (defined(__GNUC__) && !defined(__clang__))
 #define ABSL_PREDICT_FALSE(x) (__builtin_expect(x, 0))
diff --git a/absl/container/inlined_vector_benchmark.cc b/absl/container/inlined_vector_benchmark.cc
index 7bb3271b..d906997a 100644
--- a/absl/container/inlined_vector_benchmark.cc
+++ b/absl/container/inlined_vector_benchmark.cc
@@ -405,12 +405,6 @@ class NontrivialType {
 
 using NontrivialVec = absl::InlinedVector<NontrivialType, kInlineElements>;
 
-#define BENCHMARK_OPERATION(BM_Function)                      \
-  BENCHMARK_TEMPLATE(BM_Function, TrivialVec, kSmallSize);    \
-  BENCHMARK_TEMPLATE(BM_Function, TrivialVec, kLargeSize);    \
-  BENCHMARK_TEMPLATE(BM_Function, NontrivialVec, kSmallSize); \
-  BENCHMARK_TEMPLATE(BM_Function, NontrivialVec, kLargeSize)
-
 template <typename VecT, typename PrepareVec, typename TestVec>
 void BatchedBenchmark(benchmark::State& state, PrepareVec prepare_vec,
                       TestVec test_vec) {
@@ -432,13 +426,18 @@ void BatchedBenchmark(benchmark::State& state, PrepareVec prepare_vec,
   }
 }
 
-template <typename VecT, size_t Size>
+template <typename VecT, size_t FromSize>
 void BM_Clear(benchmark::State& state) {
   BatchedBenchmark<VecT>(
       state,
-      /* prepare_vec = */ [](VecT* vec) { vec->resize(Size); },
+      /* prepare_vec = */ [](VecT* vec) { vec->resize(FromSize); },
       /* test_vec = */ [](VecT* vec) { vec->clear(); });
 }
-BENCHMARK_OPERATION(BM_Clear);
+
+BENCHMARK_TEMPLATE(BM_Clear, TrivialVec, kSmallSize);
+BENCHMARK_TEMPLATE(BM_Clear, TrivialVec, kLargeSize);
+
+BENCHMARK_TEMPLATE(BM_Clear, NontrivialVec, kSmallSize);
+BENCHMARK_TEMPLATE(BM_Clear, NontrivialVec, kLargeSize);
 
 }  // namespace
diff --git a/absl/hash/hash_test.cc b/absl/hash/hash_test.cc
index 92c64ad5..449e77b4 100644
--- a/absl/hash/hash_test.cc
+++ b/absl/hash/hash_test.cc
@@ -470,7 +470,7 @@ TEST(IsHashableTest, PoisonHash) {
 struct NoOp {
   template <typename HashCode>
   friend HashCode AbslHashValue(HashCode h, NoOp n) {
-    return std::move(h);
+    return h;
   }
 };