Add a perf-sanity test

test/perf-sanity.cc

@@ -0,0 +1,26 @@
+// A quick and dirty performance test.
+// For actual benchmarks see https://github.com/fmtlib/format-benchmark.
+
+#include <atomic>
+#include <chrono>
+#include <iterator>
+
+#include "fmt/format.h"
+
+int main() {
+  const int n = 10000000;
+
+  auto start = std::chrono::steady_clock::now();
+  for (int iteration = 0; iteration < n; ++iteration) {
+    auto buf = fmt::memory_buffer();
+    fmt::format_to(std::back_inserter(buf),
+                   "Hello, {}. The answer is {} and {}.", 1, 2345, 6789);
+  }
+  std::atomic_signal_fence(std::memory_order_acq_rel);  // Clobber memory.
+  auto end = std::chrono::steady_clock::now();
+
+  std::chrono::duration<double> duration = end - start;
+  double total_time = duration.count() * 1000;  // Convert to milliseconds.
+  fmt::print("Total time for formatting {} strings: {:.1f} ms.\n", n,
+             total_time);
+}