Cleanup and optimize Range generation.

src/benchmark.cc

@@ -547,7 +547,7 @@ void BenchmarkImp::Args(const std::vector<int>& args)
 
 void BenchmarkImp::Ranges(const std::vector<std::pair<int, int>>& ranges) {
   std::vector<std::vector<int>> arglists(ranges.size());
-  int total = 1;
+  std::size_t total = 1;
   for (std::size_t i = 0; i < ranges.size(); i++) {
     AddRange(&arglists[i], ranges[i].first, ranges[i].second, range_multiplier_);
     total *= arglists[i].size();
@@ -555,14 +555,15 @@ void BenchmarkImp::Ranges(const std::vector<std::pair<int, int>>& ranges) {
 
   std::vector<std::size_t> ctr(arglists.size(), 0);
 
-  for (int i = 0; i < total; i++) {
+  for (std::size_t i = 0; i < total; i++) {
     std::vector<int> tmp;
+    tmp.reserve(arglists.size());
 
     for (std::size_t j = 0; j < arglists.size(); j++) {
       tmp.push_back(arglists[j][ctr[j]]);
     }
 
-    args_.push_back(tmp);
+    args_.push_back(std::move(tmp));
 
     for (std::size_t j = 0; j < arglists.size(); j++) {
       if (ctr[j] + 1 < arglists[j].size()) {