Export of internal Abseil changes

--
a9ac6567c0933d786d68c10011e3f3ff9deedf89 by Greg Falcon <gfalcon@google.com>:

Add absl::FunctionRef, a type analogous to the proposed C++23 std::function_ref.

Like std::function, FunctionRef can be used to type-erase any callable (invokable) object.  However, FunctionRef works by reference: it does not store a copy of the type-erased object.  If the wrapped object is destroyed before the FunctionRef, the reference becomes dangling.

FunctionRef relates to std::function in much the same way that string_view relates to std::string.

Because of these limitations, FunctionRef is best used only as a function argument type, and only where the function will be invoked immediately (rather than saved for later use).  When `const std::function<...>&` is used in this way, `absl::FunctionRef<...>` is a better-performing replacement.

PiperOrigin-RevId: 275484044

--
1f7c4df3760f8b93e5a5baf40b070eca1d3f4c98 by Abseil Team <absl-team@google.com>:

Add FastHexToBufferZeroPad16() function for blazingly fast hex encoding of uint64_t.

PiperOrigin-RevId: 275420901

--
08d48ac004eba57cf2f1ada827181a2995f74807 by Abseil Team <absl-team@google.com>:

Avoid applying the workaround for MSVC's static initialization problems when using clang-cl.

PiperOrigin-RevId: 275366326

--
40be82bd2b34670b5458c0a72a0475086153c2d6 by Abseil Team <absl-team@google.com>:

Added comments to SimpleAtof()/SimpleAtod() that clarify that they
always use the "C" locale, unlike the standard functions strtod()
and strtof() referenced now in the comments.

PiperOrigin-RevId: 275355815

--
086779dacb3f6f2b3ab59947e94e79046bdb1fe1 by Jorg Brown <jorg@google.com>:

Move the hex conversion table used by escaping.cc into numbers.h so
that other parts of Abseil can more efficiently access it.

PiperOrigin-RevId: 275331251

--
3c4ed1b04e55d96a40cbe70fb70929ffbb0c0432 by Abseil Team <absl-team@google.com>:

Avoid applying the workaround for MSVC's static initialization problems when using clang-cl.

PiperOrigin-RevId: 275323858

--
56ceb58ab688c3761978308609b09a1ac2739c9a by Derek Mauro <dmauro@google.com>:

Add script for testing on Alpine Linux (for musl test coverage)

PiperOrigin-RevId: 275321244
GitOrigin-RevId: a9ac6567c0933d786d68c10011e3f3ff9deedf89
Change-Id: I39799fa03768ddb44f3166200c860e1da4461807

1 files changed, 140 insertions, 0 deletions

diff --git a/absl/functional/function_ref_benchmark.cc b/absl/functional/function_ref_benchmark.cc
new file mode 100644
index 0000000..f6dfcab
--- /dev/null
+++ b/absl/functional/function_ref_benchmark.cc
@@ -0,0 +1,140 @@
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/functional/function_ref.h"
+
+#include <memory>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/attributes.h"
+
+namespace absl {
+namespace {
+
+int dummy = 0;
+
+void FreeFunction() { benchmark::DoNotOptimize(dummy); }
+
+struct TrivialFunctor {
+  void operator()() const { benchmark::DoNotOptimize(dummy); }
+};
+
+struct LargeFunctor {
+  void operator()() const { benchmark::DoNotOptimize(this); }
+  std::string a, b, c;
+};
+
+template <typename Function, typename... Args>
+void ABSL_ATTRIBUTE_NOINLINE CallFunction(Function f, Args&&... args) {
+  f(std::forward<Args>(args)...);
+}
+
+template <typename Function, typename Callable, typename... Args>
+void ConstructAndCallFunctionBenchmark(benchmark::State& state,
+                                       const Callable& c, Args&&... args) {
+  for (auto _ : state) {
+    CallFunction<Function>(c, std::forward<Args>(args)...);
+  }
+}
+
+void BM_TrivialStdFunction(benchmark::State& state) {
+  ConstructAndCallFunctionBenchmark<std::function<void()>>(state,
+                                                           TrivialFunctor{});
+}
+BENCHMARK(BM_TrivialStdFunction);
+
+void BM_TrivialFunctionRef(benchmark::State& state) {
+  ConstructAndCallFunctionBenchmark<FunctionRef<void()>>(state,
+                                                         TrivialFunctor{});
+}
+BENCHMARK(BM_TrivialFunctionRef);
+
+void BM_LargeStdFunction(benchmark::State& state) {
+  ConstructAndCallFunctionBenchmark<std::function<void()>>(state,
+                                                           LargeFunctor{});
+}
+BENCHMARK(BM_LargeStdFunction);
+
+void BM_LargeFunctionRef(benchmark::State& state) {
+  ConstructAndCallFunctionBenchmark<FunctionRef<void()>>(state, LargeFunctor{});
+}
+BENCHMARK(BM_LargeFunctionRef);
+
+void BM_FunPtrStdFunction(benchmark::State& state) {
+  ConstructAndCallFunctionBenchmark<std::function<void()>>(state, FreeFunction);
+}
+BENCHMARK(BM_FunPtrStdFunction);
+
+void BM_FunPtrFunctionRef(benchmark::State& state) {
+  ConstructAndCallFunctionBenchmark<FunctionRef<void()>>(state, FreeFunction);
+}
+BENCHMARK(BM_FunPtrFunctionRef);
+
+// Doesn't include construction or copy overhead in the loop.
+template <typename Function, typename Callable, typename... Args>
+void CallFunctionBenchmark(benchmark::State& state, const Callable& c,
+                           Args... args) {
+  Function f = c;
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(&f);
+    f(args...);
+  }
+}
+
+struct FunctorWithTrivialArgs {
+  void operator()(int a, int b, int c) const {
+    benchmark::DoNotOptimize(a);
+    benchmark::DoNotOptimize(b);
+    benchmark::DoNotOptimize(c);
+  }
+};
+
+void BM_TrivialArgsStdFunction(benchmark::State& state) {
+  CallFunctionBenchmark<std::function<void(int, int, int)>>(
+      state, FunctorWithTrivialArgs{}, 1, 2, 3);
+}
+BENCHMARK(BM_TrivialArgsStdFunction);
+
+void BM_TrivialArgsFunctionRef(benchmark::State& state) {
+  CallFunctionBenchmark<FunctionRef<void(int, int, int)>>(
+      state, FunctorWithTrivialArgs{}, 1, 2, 3);
+}
+BENCHMARK(BM_TrivialArgsFunctionRef);
+
+struct FunctorWithNonTrivialArgs {
+  void operator()(std::string a, std::string b, std::string c) const {
+    benchmark::DoNotOptimize(&a);
+    benchmark::DoNotOptimize(&b);
+    benchmark::DoNotOptimize(&c);
+  }
+};
+
+void BM_NonTrivialArgsStdFunction(benchmark::State& state) {
+  std::string a, b, c;
+  CallFunctionBenchmark<
+      std::function<void(std::string, std::string, std::string)>>(
+      state, FunctorWithNonTrivialArgs{}, a, b, c);
+}
+BENCHMARK(BM_NonTrivialArgsStdFunction);
+
+void BM_NonTrivialArgsFunctionRef(benchmark::State& state) {
+  std::string a, b, c;
+  CallFunctionBenchmark<
+      FunctionRef<void(std::string, std::string, std::string)>>(
+      state, FunctorWithNonTrivialArgs{}, a, b, c);
+}
+BENCHMARK(BM_NonTrivialArgsFunctionRef);
+
+}  // namespace
+}  // namespace absl