Optimize filesystem::path by providing weaker exception guarantees.
path uses string::append to construct, append, and concatenate paths. Unfortunatly
string::append has a strong exception safety guaranteed and if it can't prove
that the iterator operations don't throw then it will allocate a temporary
string copy to append to. However this extra allocation and copy is very
undesirable for path which doesn't have the same exception guarantees.
To work around this this patch adds string::__append_forward_unsafe which exposes
the std::string::append interface for forward iterators without enforcing
that the iterator is noexcept.
llvm-svn: 285532
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: a55333003d33ceb5857c315093bdd7e58af4ee92
diff --git a/benchmarks/filesystem.bench.cpp b/benchmarks/filesystem.bench.cpp
index 2cea3f6..f7949a1 100644
--- a/benchmarks/filesystem.bench.cpp
+++ b/benchmarks/filesystem.bench.cpp
@@ -2,6 +2,7 @@
#include "benchmark/benchmark_api.h"
#include "GenerateInput.hpp"
+#include "test_iterators.h"
namespace fs = std::experimental::filesystem;
@@ -41,6 +42,39 @@
BENCHMARK_CAPTURE(BM_PathConstructCStr, large_string,
getRandomStringInputs)->Arg(TestNumInputs);
+
+template <template <class...> class ItType, class GenInputs>
+void BM_PathConstructIter(benchmark::State &st, GenInputs gen) {
+ using namespace fs;
+ using Iter = ItType<std::string::const_iterator>;
+ const auto in = gen(st.range(0));
+ path PP;
+ for (auto& Part : in)
+ PP /= Part;
+ auto Start = Iter(PP.native().begin());
+ auto End = Iter(PP.native().end());
+ benchmark::DoNotOptimize(PP.native().data());
+ benchmark::DoNotOptimize(Start);
+ benchmark::DoNotOptimize(End);
+ while (st.KeepRunning()) {
+ const path P(Start, End);
+ benchmark::DoNotOptimize(P.native().data());
+ }
+}
+template <class GenInputs>
+void BM_PathConstructInputIter(benchmark::State &st, GenInputs gen) {
+ BM_PathConstructIter<input_iterator>(st, gen);
+}
+template <class GenInputs>
+void BM_PathConstructForwardIter(benchmark::State &st, GenInputs gen) {
+ BM_PathConstructIter<forward_iterator>(st, gen);
+}
+BENCHMARK_CAPTURE(BM_PathConstructInputIter, large_string,
+ getRandomStringInputs)->Arg(TestNumInputs);
+BENCHMARK_CAPTURE(BM_PathConstructForwardIter, large_string,
+ getRandomStringInputs)->Arg(TestNumInputs);
+
+
template <class GenInputs>
void BM_PathIterateMultipleTimes(benchmark::State &st, GenInputs gen) {
using namespace fs;