Export of internal Abseil changes.

--
ee19e203eca970ff88e8f25ce4e19c32e143b988 by Jon Cohen <cohenjon@google.com>:

Exception safety testing no longer uses absl::optional

PiperOrigin-RevId: 220336204

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460666eb0b316a8b4aeedc589644d53b05251bd1 by Derek Mauro <dmauro@google.com>:

Rework SwissTable SSE2 support
  - Use SSE2 on MSVC when available
    https://github.com/abseil/abseil-cpp/issues/210
  - Emulate _mm_cmpgt_epi8 with other SSE2 instructions when using
    -funsigned-char under GCC
    https://github.com/abseil/abseil-cpp/issues/209

PiperOrigin-RevId: 220312351

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1f4318ecedf8d539b7b698eb803d613ad6b69278 by Abseil Team <absl-team@google.com>:

Change CollectPerfectRatios to use 10 trials to smooth out the outliers in the
sample.

PiperOrigin-RevId: 220286579

--
6755abc2673553a7f578bb29c6e9ca8d991bc9c8 by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 220274307

--
8645b6187329ebf0aaf3c2de2888ba44466cd879 by Abseil Team <absl-team@google.com>:

* #endif for a header guard should reference the guard macro in a comment

PiperOrigin-RevId: 220206868

--
3987a7ad11319230910931cd2468b60b3fd1b85c by Gennadiy Civil <misterg@google.com>:

Internal Change

PiperOrigin-RevId: 220136674

--
cc908c1db2ee0d4523dc813e33f600583bb986c5 by Abseil Team <absl-team@google.com>:

absl: fix backoff logic in SpinLockWait

There are 3 bugs in loop variable handling:
1. It starts with 0, but AbslInternalSpinLockDelay ignores loop == 0.
So it does not actually wait when it should.
2. loop is incremented after successful state changes,
but it should not (why would be increase backoff delay after that?).
3. loop is incremented after CAS failures,
but it should not (why would be increase backoff delay after that?).

Use the same handling of loop as used in SpinLock.

PiperOrigin-RevId: 220136079

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a0a1c6ef5910ebd28e07215d7df03cc0da0b3eed by Abseil Team <absl-team@google.com>:

absl: relax unnecessarily strong memory ordering in SpinLock::SlowLock

We don't need to acquire visibility over anything when setting kSpinLockSleeper.
Replace the confusing and unnecessarily strong memory order with relaxed.

PiperOrigin-RevId: 220023380

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c50858b51af28b9fca1a62616324f85f3e84ea74 by Tom Manshreck <shreck@google.com>:

Update comments in flat_hash_map, node_hash_{set, map} and the containers developer guide

PiperOrigin-RevId: 219938692

--
e87b7d1a5f61e165b1c44d3b16d8d967197cdfce by CJ Johnson <johnsoncj@google.com>:

Rearranges the public methods of InlinedVector and cleans up the comments

PiperOrigin-RevId: 219896257

--
f3234c466f792e0fc4bfd21fc7919dba5e679375 by CJ Johnson <johnsoncj@google.com>:

Adds branch prediction to exceptional early exit cases of inlined vector's API

PiperOrigin-RevId: 219887173

--
4dfccf1a81ca0425912d3da25a8470f78c532ce4 by CJ Johnson <johnsoncj@google.com>:

Fixes the InlinedVector public interface to use the allocator type references instead of assuming the type
Also cleans up some cruft in formatting and comments

PiperOrigin-RevId: 219878876

--
4bb6a2b892abb10bd6a424db7e94ed8640802470 by Tom Manshreck <shreck@google.com>:

Add comments on constructor and assignment operator support to flat_hash_set

PiperOrigin-RevId: 219825338

--
c23f973e2f7f4feea0da36bf8a9c3f8a8954bb74 by Abseil Team <absl-team@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 219823847
GitOrigin-RevId: ee19e203eca970ff88e8f25ce4e19c32e143b988
Change-Id: I288c927ca481dc57340420dbb4c278a05cf15e83

1 files changed, 40 insertions, 0 deletions

diff --git a/absl/container/flat_hash_set.h b/absl/container/flat_hash_set.h
index 04fa73f1..a2584d66 100644
--- a/absl/container/flat_hash_set.h
+++ b/absl/container/flat_hash_set.h
@@ -102,6 +102,46 @@ class flat_hash_set
   using Base = typename flat_hash_set::raw_hash_set;
 
  public:
+  // Constructors and Assignment Operators
+  //
+  // A flat_hash_set supports the same overload set as `std::unordered_map`
+  // for construction and assignment:
+  //
+  // *  Default constructor
+  //
+  //    // No allocation for the table's elements is made.
+  //    absl::flat_hash_set<std::string> set1;
+  //
+  // * Initializer List constructor
+  //
+  //   absl::flat_hash_set<std::string> set2 =
+  //       {{"huey"}, {"dewey"}, {"louie"},};
+  //
+  // * Copy constructor
+  //
+  //   absl::flat_hash_set<std::string> set3(set2);
+  //
+  // * Copy assignment operator
+  //
+  //  // Hash functor and Comparator are copied as well
+  //  absl::flat_hash_set<std::string> set4;
+  //  set4 = set3;
+  //
+  // * Move constructor
+  //
+  //   // Move is guaranteed efficient
+  //   absl::flat_hash_set<std::string> set5(std::move(set4));
+  //
+  // * Move assignment operator
+  //
+  //   // May be efficient if allocators are compatible
+  //   absl::flat_hash_set<std::string> set6;
+  //   set6 = std::move(set5);
+  //
+  // * Range constructor
+  //
+  //   std::vector<std::string> v = {"a", "b"};
+  //   absl::flat_hash_set<std::string> set7(v.begin(), v.end());
   flat_hash_set() {}
   using Base::Base;