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+// Copyright 2018 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/strings/string_view.h"
+
+#include <algorithm>
+#include <cstdint>
+#include <map>
+#include <random>
+#include <string>
+#include <unordered_set>
+#include <vector>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/attributes.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/macros.h"
+#include "absl/strings/str_cat.h"
+
+namespace {
+
+void BM_StringViewFromString(benchmark::State& state) {
+ std::string s(state.range(0), 'x');
+ std::string* ps = &s;
+ struct SV {
+ SV() = default;
+ explicit SV(const std::string& s) : sv(s) {}
+ absl::string_view sv;
+ } sv;
+ SV* psv = &sv;
+ benchmark::DoNotOptimize(ps);
+ benchmark::DoNotOptimize(psv);
+ for (auto _ : state) {
+ new (psv) SV(*ps);
+ benchmark::DoNotOptimize(sv);
+ }
+}
+BENCHMARK(BM_StringViewFromString)->Arg(12)->Arg(128);
+
+// Provide a forcibly out-of-line wrapper for operator== that can be used in
+// benchmarks to measure the impact of inlining.
+ABSL_ATTRIBUTE_NOINLINE
+bool NonInlinedEq(absl::string_view a, absl::string_view b) { return a == b; }
+
+// We use functions that cannot be inlined to perform the comparison loops so
+// that inlining of the operator== can't optimize away *everything*.
+ABSL_ATTRIBUTE_NOINLINE
+void DoEqualityComparisons(benchmark::State& state, absl::string_view a,
+ absl::string_view b) {
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(a == b);
+ }
+}
+
+void BM_EqualIdentical(benchmark::State& state) {
+ std::string x(state.range(0), 'a');
+ DoEqualityComparisons(state, x, x);
+}
+BENCHMARK(BM_EqualIdentical)->DenseRange(0, 3)->Range(4, 1 << 10);
+
+void BM_EqualSame(benchmark::State& state) {
+ std::string x(state.range(0), 'a');
+ std::string y = x;
+ DoEqualityComparisons(state, x, y);
+}
+BENCHMARK(BM_EqualSame)
+ ->DenseRange(0, 10)
+ ->Arg(20)
+ ->Arg(40)
+ ->Arg(70)
+ ->Arg(110)
+ ->Range(160, 4096);
+
+void BM_EqualDifferent(benchmark::State& state) {
+ const int len = state.range(0);
+ std::string x(len, 'a');
+ std::string y = x;
+ if (len > 0) {
+ y[len - 1] = 'b';
+ }
+ DoEqualityComparisons(state, x, y);
+}
+BENCHMARK(BM_EqualDifferent)->DenseRange(0, 3)->Range(4, 1 << 10);
+
+// This benchmark is intended to check that important simplifications can be
+// made with absl::string_view comparisons against constant strings. The idea is
+// that if constant strings cause redundant components of the comparison, the
+// compiler should detect and eliminate them. Here we use 8 different strings,
+// each with the same size. Provided our comparison makes the implementation
+// inline-able by the compiler, it should fold all of these away into a single
+// size check once per loop iteration.
+ABSL_ATTRIBUTE_NOINLINE
+void DoConstantSizeInlinedEqualityComparisons(benchmark::State& state,
+ absl::string_view a) {
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(a == "aaa");
+ benchmark::DoNotOptimize(a == "bbb");
+ benchmark::DoNotOptimize(a == "ccc");
+ benchmark::DoNotOptimize(a == "ddd");
+ benchmark::DoNotOptimize(a == "eee");
+ benchmark::DoNotOptimize(a == "fff");
+ benchmark::DoNotOptimize(a == "ggg");
+ benchmark::DoNotOptimize(a == "hhh");
+ }
+}
+void BM_EqualConstantSizeInlined(benchmark::State& state) {
+ std::string x(state.range(0), 'a');
+ DoConstantSizeInlinedEqualityComparisons(state, x);
+}
+// We only need to check for size of 3, and <> 3 as this benchmark only has to
+// do with size differences.
+BENCHMARK(BM_EqualConstantSizeInlined)->DenseRange(2, 4);
+
+// This benchmark exists purely to give context to the above timings: this is
+// what they would look like if the compiler is completely unable to simplify
+// between two comparisons when they are comparing against constant strings.
+ABSL_ATTRIBUTE_NOINLINE
+void DoConstantSizeNonInlinedEqualityComparisons(benchmark::State& state,
+ absl::string_view a) {
+ for (auto _ : state) {
+ // Force these out-of-line to compare with the above function.
+ benchmark::DoNotOptimize(NonInlinedEq(a, "aaa"));
+ benchmark::DoNotOptimize(NonInlinedEq(a, "bbb"));
+ benchmark::DoNotOptimize(NonInlinedEq(a, "ccc"));
+ benchmark::DoNotOptimize(NonInlinedEq(a, "ddd"));
+ benchmark::DoNotOptimize(NonInlinedEq(a, "eee"));
+ benchmark::DoNotOptimize(NonInlinedEq(a, "fff"));
+ benchmark::DoNotOptimize(NonInlinedEq(a, "ggg"));
+ benchmark::DoNotOptimize(NonInlinedEq(a, "hhh"));
+ }
+}
+
+void BM_EqualConstantSizeNonInlined(benchmark::State& state) {
+ std::string x(state.range(0), 'a');
+ DoConstantSizeNonInlinedEqualityComparisons(state, x);
+}
+// We only need to check for size of 3, and <> 3 as this benchmark only has to
+// do with size differences.
+BENCHMARK(BM_EqualConstantSizeNonInlined)->DenseRange(2, 4);
+
+void BM_CompareSame(benchmark::State& state) {
+ const int len = state.range(0);
+ std::string x;
+ for (int i = 0; i < len; i++) {
+ x += 'a';
+ }
+ std::string y = x;
+ absl::string_view a = x;
+ absl::string_view b = y;
+
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(a);
+ benchmark::DoNotOptimize(b);
+ benchmark::DoNotOptimize(a.compare(b));
+ }
+}
+BENCHMARK(BM_CompareSame)->DenseRange(0, 3)->Range(4, 1 << 10);
+
+void BM_CompareFirstOneLess(benchmark::State& state) {
+ const int len = state.range(0);
+ std::string x(len, 'a');
+ std::string y = x;
+ y.back() = 'b';
+ absl::string_view a = x;
+ absl::string_view b = y;
+
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(a);
+ benchmark::DoNotOptimize(b);
+ benchmark::DoNotOptimize(a.compare(b));
+ }
+}
+BENCHMARK(BM_CompareFirstOneLess)->DenseRange(1, 3)->Range(4, 1 << 10);
+
+void BM_CompareSecondOneLess(benchmark::State& state) {
+ const int len = state.range(0);
+ std::string x(len, 'a');
+ std::string y = x;
+ x.back() = 'b';
+ absl::string_view a = x;
+ absl::string_view b = y;
+
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(a);
+ benchmark::DoNotOptimize(b);
+ benchmark::DoNotOptimize(a.compare(b));
+ }
+}
+BENCHMARK(BM_CompareSecondOneLess)->DenseRange(1, 3)->Range(4, 1 << 10);
+
+void BM_find_string_view_len_one(benchmark::State& state) {
+ std::string haystack(state.range(0), '0');
+ absl::string_view s(haystack);
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(s.find("x")); // not present; length 1
+ }
+}
+BENCHMARK(BM_find_string_view_len_one)->Range(1, 1 << 20);
+
+void BM_find_string_view_len_two(benchmark::State& state) {
+ std::string haystack(state.range(0), '0');
+ absl::string_view s(haystack);
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(s.find("xx")); // not present; length 2
+ }
+}
+BENCHMARK(BM_find_string_view_len_two)->Range(1, 1 << 20);
+
+void BM_find_one_char(benchmark::State& state) {
+ std::string haystack(state.range(0), '0');
+ absl::string_view s(haystack);
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(s.find('x')); // not present
+ }
+}
+BENCHMARK(BM_find_one_char)->Range(1, 1 << 20);
+
+void BM_rfind_one_char(benchmark::State& state) {
+ std::string haystack(state.range(0), '0');
+ absl::string_view s(haystack);
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(s.rfind('x')); // not present
+ }
+}
+BENCHMARK(BM_rfind_one_char)->Range(1, 1 << 20);
+
+void BM_worst_case_find_first_of(benchmark::State& state, int haystack_len) {
+ const int needle_len = state.range(0);
+ std::string needle;
+ for (int i = 0; i < needle_len; ++i) {
+ needle += 'a' + i;
+ }
+ std::string haystack(haystack_len, '0'); // 1000 zeros.
+
+ absl::string_view s(haystack);
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(s.find_first_of(needle));
+ }
+}
+
+void BM_find_first_of_short(benchmark::State& state) {
+ BM_worst_case_find_first_of(state, 10);
+}
+
+void BM_find_first_of_medium(benchmark::State& state) {
+ BM_worst_case_find_first_of(state, 100);
+}
+
+void BM_find_first_of_long(benchmark::State& state) {
+ BM_worst_case_find_first_of(state, 1000);
+}
+
+BENCHMARK(BM_find_first_of_short)->DenseRange(0, 4)->Arg(8)->Arg(16)->Arg(32);
+BENCHMARK(BM_find_first_of_medium)->DenseRange(0, 4)->Arg(8)->Arg(16)->Arg(32);
+BENCHMARK(BM_find_first_of_long)->DenseRange(0, 4)->Arg(8)->Arg(16)->Arg(32);
+
+struct EasyMap : public std::map<absl::string_view, uint64_t> {
+ explicit EasyMap(size_t) {}
+};
+
+// This templated benchmark helper function is intended to stress operator== or
+// operator< in a realistic test. It surely isn't entirely realistic, but it's
+// a start. The test creates a map of type Map, a template arg, and populates
+// it with table_size key/value pairs. Each key has WordsPerKey words. After
+// creating the map, a number of lookups are done in random order. Some keys
+// are used much more frequently than others in this phase of the test.
+template <typename Map, int WordsPerKey>
+void StringViewMapBenchmark(benchmark::State& state) {
+ const int table_size = state.range(0);
+ const double kFractionOfKeysThatAreHot = 0.2;
+ const int kNumLookupsOfHotKeys = 20;
+ const int kNumLookupsOfColdKeys = 1;
+ const char* words[] = {"the", "quick", "brown", "fox", "jumped",
+ "over", "the", "lazy", "dog", "and",
+ "found", "a", "large", "mushroom", "and",
+ "a", "couple", "crickets", "eating", "pie"};
+ // Create some keys that consist of words in random order.
+ std::random_device r;
+ std::seed_seq seed({r(), r(), r(), r(), r(), r(), r(), r()});
+ std::mt19937 rng(seed);
+ std::vector<std::string> keys(table_size);
+ std::vector<int> all_indices;
+ const int kBlockSize = 1 << 12;
+ std::unordered_set<std::string> t(kBlockSize);
+ std::uniform_int_distribution<int> uniform(0, ABSL_ARRAYSIZE(words) - 1);
+ for (int i = 0; i < table_size; i++) {
+ all_indices.push_back(i);
+ do {
+ keys[i].clear();
+ for (int j = 0; j < WordsPerKey; j++) {
+ absl::StrAppend(&keys[i], j > 0 ? " " : "", words[uniform(rng)]);
+ }
+ } while (!t.insert(keys[i]).second);
+ }
+
+ // Create a list of strings to lookup: a permutation of the array of
+ // keys we just created, with repeats. "Hot" keys get repeated more.
+ std::shuffle(all_indices.begin(), all_indices.end(), rng);
+ const int num_hot = table_size * kFractionOfKeysThatAreHot;
+ const int num_cold = table_size - num_hot;
+ std::vector<int> hot_indices(all_indices.begin(),
+ all_indices.begin() + num_hot);
+ std::vector<int> indices;
+ for (int i = 0; i < kNumLookupsOfColdKeys; i++) {
+ indices.insert(indices.end(), all_indices.begin(), all_indices.end());
+ }
+ for (int i = 0; i < kNumLookupsOfHotKeys - kNumLookupsOfColdKeys; i++) {
+ indices.insert(indices.end(), hot_indices.begin(), hot_indices.end());
+ }
+ std::shuffle(indices.begin(), indices.end(), rng);
+ ABSL_RAW_CHECK(
+ num_cold * kNumLookupsOfColdKeys + num_hot * kNumLookupsOfHotKeys ==
+ indices.size(),
+ "");
+ // After constructing the array we probe it with absl::string_views built from
+ // test_strings. This means operator== won't see equal pointers, so
+ // it'll have to check for equal lengths and equal characters.
+ std::vector<std::string> test_strings(indices.size());
+ for (int i = 0; i < indices.size(); i++) {
+ test_strings[i] = keys[indices[i]];
+ }
+
+ // Run the benchmark. It includes map construction but is mostly
+ // map lookups.
+ for (auto _ : state) {
+ Map h(table_size);
+ for (int i = 0; i < table_size; i++) {
+ h[keys[i]] = i * 2;
+ }
+ ABSL_RAW_CHECK(h.size() == table_size, "");
+ uint64_t sum = 0;
+ for (int i = 0; i < indices.size(); i++) {
+ sum += h[test_strings[i]];
+ }
+ benchmark::DoNotOptimize(sum);
+ }
+}
+
+void BM_StdMap_4(benchmark::State& state) {
+ StringViewMapBenchmark<EasyMap, 4>(state);
+}
+BENCHMARK(BM_StdMap_4)->Range(1 << 10, 1 << 16);
+
+void BM_StdMap_8(benchmark::State& state) {
+ StringViewMapBenchmark<EasyMap, 8>(state);
+}
+BENCHMARK(BM_StdMap_8)->Range(1 << 10, 1 << 16);
+
+void BM_CopyToStringNative(benchmark::State& state) {
+ std::string src(state.range(0), 'x');
+ absl::string_view sv(src);
+ std::string dst;
+ for (auto _ : state) {
+ dst.assign(sv.begin(), sv.end());
+ }
+}
+BENCHMARK(BM_CopyToStringNative)->Range(1 << 3, 1 << 12);
+
+void BM_AppendToStringNative(benchmark::State& state) {
+ std::string src(state.range(0), 'x');
+ absl::string_view sv(src);
+ std::string dst;
+ for (auto _ : state) {
+ dst.clear();
+ dst.insert(dst.end(), sv.begin(), sv.end());
+ }
+}
+BENCHMARK(BM_AppendToStringNative)->Range(1 << 3, 1 << 12);
+
+} // namespace
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