[libc++] Don't run multithreaded stringstream benchmarks

[ldionne]

This results in invalid JSON output as reported
in google/benchmark#2039.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Louis Dionne (ldionne)

Changes

This results in invalid JSON output as reported
in google/benchmark#2039.

---

Full diff: https://github.com/llvm/llvm-project/pull/158294.diff

1 Files Affected:

• (modified) libcxx/test/benchmarks/stringstream.bench.cpp (+2-2)

diff --git a/libcxx/test/benchmarks/stringstream.bench.cpp b/libcxx/test/benchmarks/stringstream.bench.cpp
index b7c50a96ef51e..367024c49ac69 100644
--- a/libcxx/test/benchmarks/stringstream.bench.cpp
+++ b/libcxx/test/benchmarks/stringstream.bench.cpp
@@ -80,7 +80,7 @@ static void BM_Istream_numbers(benchmark::State& state) {
   while (state.KeepRunning())
     benchmark::DoNotOptimize(i += istream_numbers(sel.imbue));
 }
-BENCHMARK(BM_Istream_numbers)->DenseRange(0, 3)->UseRealTime()->Threads(1)->ThreadPerCpu();
+BENCHMARK(BM_Istream_numbers)->DenseRange(0, 3);
 
 static void BM_Ostream_number(benchmark::State& state) {
   LocaleSelector sel(state);
@@ -92,6 +92,6 @@ static void BM_Ostream_number(benchmark::State& state) {
     benchmark::DoNotOptimize(ss.str().c_str());
   }
 }
-BENCHMARK(BM_Ostream_number)->DenseRange(0, 3)->UseRealTime()->Threads(1)->ThreadPerCpu();
+BENCHMARK(BM_Ostream_number)->DenseRange(0, 3);
 
 BENCHMARK_MAIN();

[ldionne]

/libcxx-bot benchmark libcxx/test/benchmarks/stringstream.bench.cpp

Benchmark results:

Benchmark               Baseline    Candidate    Difference    % Difference
--------------------  ----------  -----------  ------------  --------------
BM_Istream_numbers/0     4273.79      4197.29        -76.50           -1.79
BM_Istream_numbers/1     4341.77      4294.81        -46.97           -1.08
BM_Istream_numbers/2     4721.12      4258.11       -463.01           -9.81
BM_Istream_numbers/3     4452.55      4167.05       -285.50           -6.41
BM_Ostream_number/0       105.01        99.99         -5.03           -4.79
BM_Ostream_number/1       138.38       129.90         -8.49           -6.13
BM_Ostream_number/2       137.09       130.61         -6.47           -4.72
BM_Ostream_number/3       103.95       101.45         -2.50           -2.41