Export of internal Abseil changes

--
be02479c8f5ddf18f0d711e86648a2a0a9823fb6 by Gennadiy Rozental <rogeeff@google.com>:

Suppress MSVC warning about unused return value

PiperOrigin-RevId: 348624511

--
10e6da15e34d84d314fc1eca1bcdeb96538a04d1 by Derek Mauro <dmauro@google.com>:

Add additional information to README.md

PiperOrigin-RevId: 348562436

--
57283e13d221d9a3f6678a1c6db1a41b4421b938 by Jorg Brown <jorg@google.com>:

Tweaks for better AArch64 support under MSVC

PiperOrigin-RevId: 348518028

--
48cb64ed90c71db6342dcf478a03bbb419b98500 by Christian Blichmann <cblichmann@google.com>:

Internal change

PiperOrigin-RevId: 348480642
GitOrigin-RevId: be02479c8f5ddf18f0d711e86648a2a0a9823fb6
Change-Id: I3614bf846ad1b99e34f507346da1252c6bbc13ba

5 files changed, 42 insertions, 19 deletions

diff --git a/README.md b/README.md
index f1802349..76f1d1e1 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,9 @@ standard library.
 - [About Abseil](#about)
 - [Quickstart](#quickstart)
 - [Building Abseil](#build)
+- [Support](#support)
 - [Codemap](#codemap)
+- [Releases](#releases)
 - [License](#license)
 - [Links](#links)
 
@@ -42,14 +44,22 @@ the Abseil code, running tests, and getting a simple binary working.
 <a name="build"></a>
 ## Building Abseil
 
-[Bazel](https://bazel.build) is the official build system for Abseil,
-which is supported on most major platforms (Linux, Windows, macOS, for example)
-and compilers. See the [quickstart](https://abseil.io/docs/cpp/quickstart) for
-more information on building Abseil using the Bazel build system.
+[Bazel](https://bazel.build) and [CMake](https://cmake.org/) are the official
+build systems for Abseil.
 
-<a name="cmake"></a>
-If you require CMake support, please check the
-[CMake build instructions](CMake/README.md).
+See the [quickstart](https://abseil.io/docs/cpp/quickstart) for more information
+on building Abseil using the Bazel build system.
+
+If you require CMake support, please check the [CMake build
+instructions](CMake/README.md) and [CMake
+Quickstart](https://abseil.io/docs/cpp/quickstart-cmake).
+
+## Support
+
+Abseil is officially supported on many platforms. See the [Abseil
+platform support
+guide](https://abseil.io/docs/cpp/platforms/platforms) for details on
+supported operating systems, compilers, CPUs, etc.
 
 ## Codemap
 
@@ -100,6 +110,15 @@ Abseil contains the following C++ library components:
 * [`utility`](absl/utility/)
   <br /> The `utility` library contains utility and helper code.
 
+## Releases
+
+Abseil recommends users "live-at-head" (update to the latest commit from the
+master branch as often as possible). However, we realize this philosophy doesn't
+work for every project, so we also provide [Long Term Support
+Releases](https://github.com/abseil/abseil-cpp/releases) to which we backport
+fixes for severe bugs. See our [release
+management](https://abseil.io/about/releases) document for more details.
+
 ## License
 
 The Abseil C++ library is licensed under the terms of the Apache
diff --git a/absl/numeric/internal/bits.h b/absl/numeric/internal/bits.h
index 50828156..af45700f 100644
--- a/absl/numeric/internal/bits.h
+++ b/absl/numeric/internal/bits.h
@@ -23,12 +23,6 @@
 // windows intrinsic functions.
 #if defined(_MSC_VER) && !defined(__clang__)
 #include <intrin.h>
-#if defined(_M_X64)
-#pragma intrinsic(_BitScanReverse64)
-#pragma intrinsic(_BitScanForward64)
-#endif
-#pragma intrinsic(_BitScanReverse)
-#pragma intrinsic(_BitScanForward)
 #endif
 
 #include "absl/base/attributes.h"
@@ -185,7 +179,8 @@ CountLeadingZeroes64(uint64_t x) {
 
   // Handle 0 as a special case because __builtin_clzll(0) is undefined.
   return x == 0 ? 64 : __builtin_clzll(x);
-#elif defined(_MSC_VER) && !defined(__clang__) && defined(_M_X64)
+#elif defined(_MSC_VER) && !defined(__clang__) && \
+    (defined(_M_X64) || defined(_M_ARM64))
   // MSVC does not have __buitin_clzll. Use _BitScanReverse64.
   unsigned long result = 0;  // NOLINT(runtime/int)
   if (_BitScanReverse64(&result, x)) {
@@ -271,7 +266,8 @@ CountTrailingZeroesNonzero64(uint64_t x) {
   static_assert(sizeof(unsigned long long) == sizeof(x),  // NOLINT(runtime/int)
                 "__builtin_ctzll does not take 64-bit arg");
   return __builtin_ctzll(x);
-#elif defined(_MSC_VER) && !defined(__clang__) && defined(_M_X64)
+#elif defined(_MSC_VER) && !defined(__clang__) && \
+    (defined(_M_X64) || defined(_M_ARM64))
   unsigned long result = 0;  // NOLINT(runtime/int)
   _BitScanForward64(&result, x);
   return result;
diff --git a/absl/strings/numbers.h b/absl/strings/numbers.h
index ffc738fa..7966e250 100644
--- a/absl/strings/numbers.h
+++ b/absl/strings/numbers.h
@@ -1,3 +1,4 @@
+//
 // Copyright 2017 The Abseil Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
@@ -244,6 +245,13 @@ inline size_t FastHexToBufferZeroPad16(uint64_t val, char* out) {
 
 }  // namespace numbers_internal
 
+// SimpleAtoi()
+//
+// Converts a string to an integer, using `safe_strto?()` functions for actual
+// parsing, returning `true` if successful. The `safe_strto?()` functions apply
+// strict checking; the string must be a base-10 integer, optionally followed or
+// preceded by ASCII whitespace, with a value in the range of the corresponding
+// integer type.
 template <typename int_type>
 ABSL_MUST_USE_RESULT bool SimpleAtoi(absl::string_view str, int_type* out) {
   return numbers_internal::safe_strtoi_base(str, out, 10);
diff --git a/absl/strings/numbers_test.cc b/absl/strings/numbers_test.cc
index 27616bf8..4ab67fb6 100644
--- a/absl/strings/numbers_test.cc
+++ b/absl/strings/numbers_test.cc
@@ -46,7 +46,6 @@
 
 namespace {
 
-using absl::SimpleAtoi;
 using absl::numbers_internal::kSixDigitsToBufferSize;
 using absl::numbers_internal::safe_strto32_base;
 using absl::numbers_internal::safe_strto64_base;
@@ -56,6 +55,7 @@ using absl::numbers_internal::SixDigitsToBuffer;
 using absl::strings_internal::Itoa;
 using absl::strings_internal::strtouint32_test_cases;
 using absl::strings_internal::strtouint64_test_cases;
+using absl::SimpleAtoi;
 using testing::Eq;
 using testing::MatchesRegex;
 
@@ -380,7 +380,7 @@ TEST(NumbersTest, Atoi) {
   VerifySimpleAtoiGood<uint32_t>(42, 42);
   VerifySimpleAtoiGood<unsigned int>(42, 42);
   VerifySimpleAtoiGood<int64_t>(-42, -42);
-  VerifySimpleAtoiGood<long>(-42, -42);  // NOLINT: runtime-int
+  VerifySimpleAtoiGood<long>(-42, -42);  // NOLINT(runtime/int)
   VerifySimpleAtoiGood<uint64_t>(42, 42);
   VerifySimpleAtoiGood<size_t>(42, 42);
   VerifySimpleAtoiGood<std::string::size_type>(42, 42);
diff --git a/absl/strings/string_view_test.cc b/absl/strings/string_view_test.cc
index dcebb150..643af8f8 100644
--- a/absl/strings/string_view_test.cc
+++ b/absl/strings/string_view_test.cc
@@ -915,9 +915,9 @@ TEST(StringViewTest, At) {
   EXPECT_EQ(abc.at(1), 'b');
   EXPECT_EQ(abc.at(2), 'c');
 #ifdef ABSL_HAVE_EXCEPTIONS
-  EXPECT_THROW(abc.at(3), std::out_of_range);
+  EXPECT_THROW((void)abc.at(3), std::out_of_range);
 #else
-  ABSL_EXPECT_DEATH_IF_SUPPORTED(abc.at(3), "absl::string_view::at");
+  ABSL_EXPECT_DEATH_IF_SUPPORTED((void)abc.at(3), "absl::string_view::at");
 #endif
 }