Export of internal Abseil changes.

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3d20ce6cd6541579abecaba169d4b8716d511272 by Jon Cohen <cohenjon@google.com>:

Only use LSAN for clang version >= 3.5.  This should fix https://github.com/abseil/abseil-cpp/issues/244

PiperOrigin-RevId: 234675129

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e15bd4ec7a81aa95cc3d09fa1e0e81d58ae478fb by Conrad Parker <conradparker@google.com>:

Fix errors in apply() sample code

The following changes are made:
 * Make the example method public.
 * Give the two user functions different names to avoid confusion about
   whether apply() can select the correct overload of a function based
   on its tuple argument (it can't).
 * Pass tuple2 to the second example apply() invocation, instead of
   passing its contents individually.
 * Fix a s/tuple/tuple3/ typo in the third example apply() invocation.

PiperOrigin-RevId: 234223407

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de0ed71e21bc76ddf9fe715fdbaef74cd0df95c7 by Abseil Team <absl-team@google.com>:

First test if a macro is defined to avoid -Wundef.

ABSL clients may need to compile their code with the -Wundef warning
flag. It will be helpful if ABSL header files can be compiled without
the -Wundef warning.

How to avoid the -Wundef warning: If a macro may be undefined, we need
to first test whether the macro is defined before testing its value. We
can't rely on the C preprocessor rule that an undefined macro has the
value 0L.

PiperOrigin-RevId: 234201123

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fa484ad7dae0cac21140a96662809ecb0ec8eb5d by Abseil Team <absl-team@google.com>:

Internal change.

PiperOrigin-RevId: 234185697

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d69b1baef681e27954b065375ecf9c2320463b2b by Samuel Benzaquen <sbenza@google.com>:

Mix pointers more thoroughly.
Some pointer alignments interact badly with the mixing constant. By mixing twice we reduce this problem.

PiperOrigin-RevId: 234178401

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1041d0e474610f3a8fea0db90958857327d6da1c by Samuel Benzaquen <sbenza@google.com>:

Record rehashes in the hashtablez struct.
Only recording the probe length on insertion causes a huge overestimation of
the total probe length at any given time.

With natural growth, elements are inserted when the load factor is between
(max load/2, max load). However, after a rehash the majority of elements are
actually inserted when the load factor is less than max/2 and have a much lower
average probe length.

Also reset some values when the table is cleared.

PiperOrigin-RevId: 234013580

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299205caf3c89c47339f7409bc831746602cea84 by Mark Barolak <mbar@google.com>:

Fix a sample code snippet that assumes `absl::string_view::const_iterator` is `const char*`.  This is generally true, however in C++17 builds, absl::string_view is an alias for std::string_view and on MSVC, the std::string_view::const_iterator is an object instead of just a pointer.

PiperOrigin-RevId: 233844595

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af6c6370cf51a1e6c1469c79dfb2a486a4009136 by Abseil Team <absl-team@google.com>:

Internal change.

PiperOrigin-RevId: 233773470

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6e59e4b8e2bb6101b448f0f32b0bea81fe399ccf by Abseil Team <absl-team@google.com>:

fix typo in {Starts|Ends}WithIgnoreCase comment in match.h

PiperOrigin-RevId: 233662951
GitOrigin-RevId: 3d20ce6cd6541579abecaba169d4b8716d511272
Change-Id: Ib9a29b1c38c6aedf5d9f3f7f00596e8d30e864dd

absl/container/internal/hashtablez_sampler.h

@@ -33,6 +33,7 @@
 
 #include "absl/base/internal/per_thread_tls.h"
 #include "absl/base/optimization.h"
+#include "absl/container/internal/have_sse.h"
 #include "absl/synchronization/mutex.h"
 #include "absl/utility/utility.h"
 
@@ -82,10 +83,24 @@ struct HashtablezInfo {
   void* stack[kMaxStackDepth];
 };
 
+inline void RecordRehashSlow(HashtablezInfo* info, size_t total_probe_length) {
+#if SWISSTABLE_HAVE_SSE2
+  total_probe_length /= 16;
+#else
+  total_probe_length /= 8;
+#endif
+  info->total_probe_length.store(total_probe_length, std::memory_order_relaxed);
+  info->num_erases.store(0, std::memory_order_relaxed);
+}
+
 inline void RecordStorageChangedSlow(HashtablezInfo* info, size_t size,
                                      size_t capacity) {
   info->size.store(size, std::memory_order_relaxed);
   info->capacity.store(capacity, std::memory_order_relaxed);
+  if (size == 0) {
+    // This is a clear, reset the total/num_erases too.
+    RecordRehashSlow(info, 0);
+  }
 }
 
 void RecordInsertSlow(HashtablezInfo* info, size_t hash,
@@ -126,6 +141,11 @@ class HashtablezInfoHandle {
     RecordStorageChangedSlow(info_, size, capacity);
   }
 
+  inline void RecordRehash(size_t total_probe_length) {
+    if (ABSL_PREDICT_TRUE(info_ == nullptr)) return;
+    RecordRehashSlow(info_, total_probe_length);
+  }
+
   inline void RecordInsert(size_t hash, size_t distance_from_desired) {
     if (ABSL_PREDICT_TRUE(info_ == nullptr)) return;
     RecordInsertSlow(info_, hash, distance_from_desired);