LineageOS/android_external_libcxx
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Improve performance of constructing filesystem::path from strings.

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This patch fixes a performance bug when constructing or appending to a path
from a string or c-string. Previously we called 'push_back' to append every
single character. This caused multiple re-allocation and copies when at most
one reallocation is necessary. The new behavior is to simply call
`string::append` so it can correctly handle reallocation.

For large strings this change is a ~4x improvement. This also makes our path
faster to construct than libstdc++'s.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@285530 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eric Fiselier
2016-10-30 23:53:50 +00:00
parent 271a19ec19
commit ad1a12c312
3 changed files with 22 additions and 14 deletions
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20
benchmarks/filesystem.bench.cpp
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@@ -21,10 +21,26 @@ void BM_PathConstructString(benchmark::State &st, GenInputs gen) {
benchmark::DoNotOptimize(P.native().data());
}
}
BENCHMARK_CAPTURE(BM_PathConstructString, iterate_elements,
BENCHMARK_CAPTURE(BM_PathConstructString, large_string,
getRandomStringInputs)->Arg(TestNumInputs);
template <class GenInputs>
void BM_PathConstructCStr(benchmark::State &st, GenInputs gen) {
using namespace fs;
const auto in = gen(st.range(0));
path PP;
for (auto& Part : in)
PP /= Part;
benchmark::DoNotOptimize(PP.native().data());
while (st.KeepRunning()) {
const path P(PP.native().c_str());
benchmark::DoNotOptimize(P.native().data());
}
}
BENCHMARK_CAPTURE(BM_PathConstructCStr, large_string,
getRandomStringInputs)->Arg(TestNumInputs);
template <class GenInputs>
void BM_PathIterateMultipleTimes(benchmark::State &st, GenInputs gen) {
using namespace fs;
@@ -85,6 +101,4 @@ void BM_PathIterateOnceBackwards(benchmark::State &st, GenInputs gen) {
BENCHMARK_CAPTURE(BM_PathIterateOnceBackwards, iterate_elements,
getRandomStringInputs)->Arg(TestNumInputs);
BENCHMARK_MAIN()