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[libc++] Fold __search_substring into _Traits::find in case the second string has length 1 #160076

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Merged
merged 1 commit into from
Sep 25, 2025
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Merged

[libc++] Fold __search_substring into _Traits::find in case the second string has length 1 #160076

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7 changes: 7 additions & 0 deletions libcxx/include/__string/char_traits.h
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Original file line number Diff line number Diff line change
Expand Up @@ -369,6 +369,13 @@ _LIBCPP_HIDE_FROM_ABI inline _LIBCPP_CONSTEXPR_SINCE_CXX14 const _CharT* __searc
if (__len1 < __len2)
return __last1;

if (__builtin_constant_p(__len2 == 1) && __len2 == 1) {
auto __res = _Traits::find(__first1, __len1, *__first2);
if (__res == nullptr)
return __last1;
return __res;
}

// First element of __first2 is loop invariant.
_CharT __f2 = *__first2;
while (true) {
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39 changes: 39 additions & 0 deletions libcxx/test/benchmarks/containers/string.bench.cpp
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Expand Up @@ -60,6 +60,45 @@ static void BM_StringFindMatch2(benchmark::State& state) {
}
BENCHMARK(BM_StringFindMatch2)->Range(1, MAX_STRING_LEN / 4);

static void BM_StringFindStringLiteral(benchmark::State& state) {
std::string s;

for (int i = 0; i < state.range(0); i++)
s += 'a';

s += 'b';

benchmark::DoNotOptimize(s.data());
benchmark::ClobberMemory();
size_t pos;

for (auto _ : state) {
benchmark::DoNotOptimize(pos = s.find("b"));
benchmark::ClobberMemory();
}
}

BENCHMARK(BM_StringFindStringLiteral)->RangeMultiplier(2)->Range(8, 8 << 10);

static void BM_StringFindCharLiteral(benchmark::State& state) {
std::string s;

for (int i = 0; i < state.range(0); i++)
s += 'a';

s += 'b';

benchmark::DoNotOptimize(s.data());
benchmark::ClobberMemory();
size_t pos;

for (auto _ : state) {
benchmark::DoNotOptimize(pos = s.find('b'));
benchmark::ClobberMemory();
}
}
BENCHMARK(BM_StringFindCharLiteral)->RangeMultiplier(2)->Range(8, 8 << 10);

static void BM_StringCtorDefault(benchmark::State& state) {
for (auto _ : state) {
std::string Default;
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17 changes: 17 additions & 0 deletions libcxx/test/std/strings/basic.string/string.ops/string_find/string_size.pass.cpp
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Expand Up @@ -43,14 +43,17 @@ TEST_CONSTEXPR_CXX20 void test0() {
test(S(""), S("abcdeabcde"), 1, S::npos);
test(S(""), S("abcdeabcdeabcdeabcde"), 1, S::npos);
test(S("abcde"), S(""), 0, 0);
test(S("abcde"), S("a"), 0, 0);
test(S("abcde"), S("abcde"), 0, 0);
test(S("abcde"), S("abcdeabcde"), 0, S::npos);
test(S("abcde"), S("abcdeabcdeabcdeabcde"), 0, S::npos);
test(S("abcde"), S(""), 1, 1);
test(S("abcde"), S("a"), 1, S::npos);
test(S("abcde"), S("abcde"), 1, S::npos);
test(S("abcde"), S("abcdeabcde"), 1, S::npos);
test(S("abcde"), S("abcdeabcdeabcdeabcde"), 1, S::npos);
test(S("abcde"), S(""), 2, 2);
test(S("abcde"), S("a"), 2, S::npos);
test(S("abcde"), S("abcde"), 2, S::npos);
test(S("abcde"), S("abcdeabcde"), 2, S::npos);
test(S("abcde"), S("abcdeabcdeabcdeabcde"), 2, S::npos);
Expand All @@ -59,58 +62,72 @@ TEST_CONSTEXPR_CXX20 void test0() {
test(S("abcde"), S("abcdeabcde"), 4, S::npos);
test(S("abcde"), S("abcdeabcdeabcdeabcde"), 4, S::npos);
test(S("abcde"), S(""), 5, 5);
test(S("abcde"), S("a"), 5, S::npos);
test(S("abcde"), S("abcde"), 5, S::npos);
test(S("abcde"), S("abcdeabcde"), 5, S::npos);
test(S("abcde"), S("abcdeabcdeabcdeabcde"), 5, S::npos);
test(S("abcde"), S(""), 6, S::npos);
test(S("abcde"), S("a"), 6, S::npos);
test(S("abcde"), S("abcde"), 6, S::npos);
test(S("abcde"), S("abcdeabcde"), 6, S::npos);
test(S("abcde"), S("abcdeabcdeabcdeabcde"), 6, S::npos);
test(S("abcdeabcde"), S(""), 0, 0);
test(S("abcdeabcde"), S("a"), 0, 0);
test(S("abcdeabcde"), S("abcde"), 0, 0);
test(S("abcdeabcde"), S("abcdeabcde"), 0, 0);
test(S("abcdeabcde"), S("abcdeabcdeabcdeabcde"), 0, S::npos);
test(S("abcdeabcde"), S(""), 1, 1);
test(S("abcdeabcde"), S("a"), 1, 5);
test(S("abcdeabcde"), S("abcde"), 1, 5);
test(S("abcdeabcde"), S("abcdeabcde"), 1, S::npos);
test(S("abcdeabcde"), S("abcdeabcdeabcdeabcde"), 1, S::npos);
test(S("abcdeabcde"), S(""), 5, 5);
test(S("abcdeabcde"), S("a"), 5, 5);
test(S("abcdeabcde"), S("abcde"), 5, 5);
test(S("abcdeabcde"), S("abcdeabcde"), 5, S::npos);
test(S("abcdeabcde"), S("abcdeabcdeabcdeabcde"), 5, S::npos);
test(S("abcdeabcde"), S(""), 9, 9);
test(S("abcdeabcde"), S("a"), 9, S::npos);
test(S("abcdeabcde"), S("abcde"), 9, S::npos);
test(S("abcdeabcde"), S("abcdeabcde"), 9, S::npos);
test(S("abcdeabcde"), S("abcdeabcdeabcdeabcde"), 9, S::npos);
test(S("abcdeabcde"), S(""), 10, 10);
test(S("abcdeabcde"), S("a"), 10, S::npos);
test(S("abcdeabcde"), S("abcde"), 10, S::npos);
test(S("abcdeabcde"), S("abcdeabcde"), 10, S::npos);
test(S("abcdeabcde"), S("abcdeabcdeabcdeabcde"), 10, S::npos);
test(S("abcdeabcde"), S(""), 11, S::npos);
test(S("abcdeabcde"), S("a"), 11, S::npos);
test(S("abcdeabcde"), S("abcde"), 11, S::npos);
test(S("abcdeabcde"), S("abcdeabcde"), 11, S::npos);
test(S("abcdeabcde"), S("abcdeabcdeabcdeabcde"), 11, S::npos);
test(S("abcdeabcdeabcdeabcde"), S(""), 0, 0);
test(S("abcdeabcdeabcdeabcde"), S("a"), 0, 0);
test(S("abcdeabcdeabcdeabcde"), S("abcde"), 0, 0);
test(S("abcdeabcdeabcdeabcde"), S("abcdeabcde"), 0, 0);
test(S("abcdeabcdeabcdeabcde"), S("abcdeabcdeabcdeabcde"), 0, 0);
test(S("abcdeabcdeabcdeabcde"), S(""), 1, 1);
test(S("abcdeabcdeabcdeabcde"), S("a"), 1, 5);
test(S("abcdeabcdeabcdeabcde"), S("abcde"), 1, 5);
test(S("abcdeabcdeabcdeabcde"), S("abcdeabcde"), 1, 5);
test(S("abcdeabcdeabcdeabcde"), S("abcdeabcdeabcdeabcde"), 1, S::npos);
test(S("abcdeabcdeabcdeabcde"), S(""), 10, 10);
test(S("abcdeabcdeabcdeabcde"), S("a"), 10, 10);
test(S("abcdeabcdeabcdeabcde"), S("abcde"), 10, 10);
test(S("abcdeabcdeabcdeabcde"), S("abcdeabcde"), 10, 10);
test(S("abcdeabcdeabcdeabcde"), S("abcdeabcdeabcdeabcde"), 10, S::npos);
test(S("abcdeabcdeabcdeabcde"), S(""), 19, 19);
test(S("abcdeabcdeabcdeabcde"), S("a"), 19, S::npos);
test(S("abcdeabcdeabcdeabcde"), S("abcde"), 19, S::npos);
test(S("abcdeabcdeabcdeabcde"), S("abcdeabcde"), 19, S::npos);
test(S("abcdeabcdeabcdeabcde"), S("abcdeabcdeabcdeabcde"), 19, S::npos);
test(S("abcdeabcdeabcdeabcde"), S(""), 20, 20);
test(S("abcdeabcdeabcdeabcde"), S("a"), 20, S::npos);
test(S("abcdeabcdeabcdeabcde"), S("abcde"), 20, S::npos);
test(S("abcdeabcdeabcdeabcde"), S("abcdeabcde"), 20, S::npos);
test(S("abcdeabcdeabcdeabcde"), S("abcdeabcdeabcdeabcde"), 20, S::npos);
test(S("abcdeabcdeabcdeabcde"), S(""), 21, S::npos);
test(S("abcdeabcdeabcdeabcde"), S("a"), 21, S::npos);
test(S("abcdeabcdeabcdeabcde"), S("abcde"), 21, S::npos);
test(S("abcdeabcdeabcdeabcde"), S("abcdeabcde"), 21, S::npos);
test(S("abcdeabcdeabcdeabcde"), S("abcdeabcdeabcdeabcde"), 21, S::npos);
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