Fix CLANG build break caused by the recent Persistent Cache change

Test Plan: USE_CLANG=1 make all check -j32

Reviewers: andrewkr, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: leveldb, andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D59313

utilities/persistent_cache/persistent_cache_test.h

@@ -58,7 +58,7 @@ class PersistentCacheTierTest : public testing::Test {
       std::thread th(fn);
       threads.push_back(std::move(th));
     }
-    return std::move(threads);
+    return threads;
   }
 
   // Wait for threads to join
@@ -75,7 +75,7 @@ class PersistentCacheTierTest : public testing::Test {
     max_keys_ = max_keys;
     // spawn threads
     auto fn = std::bind(&PersistentCacheTierTest::InsertImpl, this);
-    auto threads = std::move(SpawnThreads(nthreads, fn));
+    auto threads = SpawnThreads(nthreads, fn);
     // join with threads
     Join(std::move(threads));
     // Flush cache
@@ -90,7 +90,7 @@ class PersistentCacheTierTest : public testing::Test {
     // spawn threads
     auto fn =
         std::bind(&PersistentCacheTierTest::VerifyImpl, this, eviction_enabled);
-    auto threads = std::move(SpawnThreads(nthreads, fn));
+    auto threads = SpawnThreads(nthreads, fn);
     // join with threads
     Join(std::move(threads));
   }
@@ -232,7 +232,8 @@ class PersistentCacheDBTest : public DBTestBase {
 
   static uint32_t TestGetTickerCount(const Options& options,
                                      Tickers ticker_type) {
-    return options.statistics->getTickerCount(ticker_type);
+    return static_cast<uint32_t>(
+        options.statistics->getTickerCount(ticker_type));
   }
 
   // insert data to table

utilities/persistent_cache/volatile_tier_impl.cc

@@ -32,7 +32,7 @@ std::vector<PersistentCacheTier::TierStats> VolatileCacheTier::Stats() {
 
   std::vector<PersistentCacheTier::TierStats> tier_stats;
   if (next_tier()) {
-    tier_stats = std::move(next_tier()->Stats());
+    tier_stats = next_tier()->Stats();
   }
   tier_stats.push_back(stat);
   return tier_stats;
@@ -49,7 +49,7 @@ std::string VolatileCacheTier::PrintStats() {
      << "pagecache.volatilecache.miss_pct: " << stats_.CacheMissPct()
      << std::endl
      << PersistentCacheTier::PrintStats();
-  return std::move(ss.str());
+  return ss.str();
 }
 
 Status VolatileCacheTier::Insert(const Slice& page_key, const char* data,