Fix unused var warnings in Release mode

Summary:
MSVC does not support unused attribute at this time. A separate assignment line fixes the issue probably by being counted as usage for MSVC and it no longer complains about unused var.
Closes https://github.com/facebook/rocksdb/pull/3048

Differential Revision: D6126272

Pulled By: maysamyabandeh

fbshipit-source-id: 4907865db45fd75a39a15725c0695aaa17509c1f

db/column_family.cc

@@ -463,7 +463,8 @@ ColumnFamilyData::~ColumnFamilyData() {
   if (dummy_versions_ != nullptr) {
     // List must be empty
     assert(dummy_versions_->TEST_Next() == dummy_versions_);
-    bool deleted __attribute__((unused)) = dummy_versions_->Unref();
+    bool deleted __attribute__((unused));
+    deleted = dummy_versions_->Unref();
     assert(deleted);
   }
 

db/compaction_iterator.cc

@@ -137,8 +137,8 @@ void CompactionIterator::Next() {
     if (merge_out_iter_.Valid()) {
       key_ = merge_out_iter_.key();
       value_ = merge_out_iter_.value();
-      bool valid_key __attribute__((__unused__)) =
-          ParseInternalKey(key_, &ikey_);
+      bool valid_key __attribute__((__unused__));
+      valid_key =  ParseInternalKey(key_, &ikey_);
       // MergeUntil stops when it encounters a corrupt key and does not
       // include them in the result, so we expect the keys here to be valid.
       assert(valid_key);
@@ -334,8 +334,8 @@ void CompactionIterator::NextFromInput() {
     // If there are no snapshots, then this kv affect visibility at tip.
     // Otherwise, search though all existing snapshots to find the earliest
     // snapshot that is affected by this kv.
-    SequenceNumber last_sequence __attribute__((__unused__)) =
-        current_user_key_sequence_;
+    SequenceNumber last_sequence __attribute__((__unused__));
+    last_sequence = current_user_key_sequence_;
     current_user_key_sequence_ = ikey_.sequence;
     SequenceNumber last_snapshot = current_user_key_snapshot_;
     SequenceNumber prev_snapshot = 0;  // 0 means no previous snapshot
@@ -538,8 +538,8 @@ void CompactionIterator::NextFromInput() {
         //       These will be correctly set below.
         key_ = merge_out_iter_.key();
         value_ = merge_out_iter_.value();
-        bool valid_key __attribute__((__unused__)) =
-            ParseInternalKey(key_, &ikey_);
+        bool valid_key __attribute__((__unused__));
+        valid_key = ParseInternalKey(key_, &ikey_);
         // MergeUntil stops when it encounters a corrupt key and does not
         // include them in the result, so we expect the keys here to valid.
         assert(valid_key);

db/db_impl_compaction_flush.cc

@@ -1678,10 +1678,10 @@ Status DBImpl::BackgroundCompaction(bool* made_progress,
     env_->Schedule(&DBImpl::BGWorkBottomCompaction, ca, Env::Priority::BOTTOM,
                    this, &DBImpl::UnscheduleCallback);
   } else {
-    int output_level  __attribute__((unused)) = c->output_level();
+    int output_level  __attribute__((unused));
+    output_level = c->output_level();
     TEST_SYNC_POINT_CALLBACK("DBImpl::BackgroundCompaction:NonTrivial",
                              &output_level);
-
     SequenceNumber earliest_write_conflict_snapshot;
     std::vector<SequenceNumber> snapshot_seqs =
         snapshots_.GetAll(&earliest_write_conflict_snapshot);

db/version_set.cc

@@ -1912,7 +1912,8 @@ void VersionStorageInfo::ExtendFileRangeOverlappingInterval(
 #endif
   *start_index = mid_index + 1;
   *end_index = mid_index;
-  int count __attribute__((unused)) = 0;
+  int count __attribute__((unused));
+  count = 0;
 
   // check backwards from 'mid' to lower indices
   for (int i = mid_index; i >= 0 ; i--) {

env/mock_env.cc

@@ -379,7 +379,8 @@ class TestMemLogger : public Logger {
       const time_t seconds = now_tv.tv_sec;
       struct tm t;
       memset(&t, 0, sizeof(t));
-      auto ret __attribute__((__unused__)) = localtime_r(&seconds, &t);
+      struct tm* ret __attribute__((__unused__));
+      ret = localtime_r(&seconds, &t);
       assert(ret);
       p += snprintf(p, limit - p,
                     "%04d/%02d/%02d-%02d:%02d:%02d.%06d ",

monitoring/thread_status_updater.cc

@@ -252,7 +252,8 @@ void ThreadStatusUpdater::EraseColumnFamilyInfo(const void* cf_key) {
     ConstantColumnFamilyInfo& cf_info = cf_pair->second;
     auto db_pair = db_key_map_.find(cf_info.db_key);
     assert(db_pair != db_key_map_.end());
-    size_t result __attribute__((unused)) = db_pair->second.erase(cf_key);
+    size_t result __attribute__((unused));
+    result = db_pair->second.erase(cf_key);
     assert(result);
     cf_info_map_.erase(cf_pair);
   }

port/win/env_win.cc

@@ -74,7 +74,9 @@ WinEnvIO::WinEnvIO(Env* hosted_env)
 
   {
     LARGE_INTEGER qpf;
-    BOOL ret = QueryPerformanceFrequency(&qpf);
+    // No init as the compiler complains about unused var
+    BOOL ret;
+    ret = QueryPerformanceFrequency(&qpf);
     assert(ret == TRUE);
     perf_counter_frequency_ = qpf.QuadPart;
   }

port/win/io_win.cc

@@ -279,7 +279,8 @@ Status WinMmapFile::MapNewRegion() {
 
     if (hMap_ != NULL) {
       // Unmap the previous one
-      BOOL ret = ::CloseHandle(hMap_);
+      BOOL ret;
+      ret = ::CloseHandle(hMap_);
       assert(ret);
       hMap_ = NULL;
     }
@@ -1020,7 +1021,8 @@ Status WinDirectory::Fsync() { return Status::OK(); }
 /// WinFileLock
 
 WinFileLock::~WinFileLock() {
-  BOOL ret = ::CloseHandle(hFile_);
+  BOOL ret;
+  ret = ::CloseHandle(hFile_);
   assert(ret);
 }
 

utilities/blob_db/blob_db_impl.cc

@@ -1312,7 +1312,8 @@ Status BlobDBImpl::CloseBlobFile(std::shared_ptr<BlobFile> bfile) {
     WriteLock wl(&mutex_);
 
     if (bfile->HasTTL()) {
-      size_t erased __attribute__((__unused__)) = open_blob_files_.erase(bfile);
+      size_t erased __attribute__((__unused__));
+      erased = open_blob_files_.erase(bfile);
       assert(erased == 1);
     } else {
       auto iter = std::find(open_simple_files_.begin(),

utilities/document/json_document.cc

@@ -48,7 +48,8 @@ void InitJSONDocument(std::unique_ptr<char[]>* data,
   fbson::FbsonWriter writer;
   bool res __attribute__((unused)) = writer.writeStartArray();
   assert(res);
-  uint32_t bytesWritten __attribute__((unused)) = f(writer);
+  uint32_t bytesWritten __attribute__((unused));
+  bytesWritten = f(writer);
   assert(bytesWritten != 0);
   res = writer.writeEndArray();
   assert(res);

utilities/persistent_cache/block_cache_tier_metadata.cc

@@ -63,7 +63,8 @@ bool BlockCacheTierMetadata::Lookup(const Slice& key, LBA* lba) {
 BlockInfo* BlockCacheTierMetadata::Remove(const Slice& key) {
   BlockInfo lookup_key(key);
   BlockInfo* binfo = nullptr;
-  bool ok __attribute__((__unused__)) = block_index_.Erase(&lookup_key, &binfo);
+  bool ok __attribute__((__unused__));
+  ok = block_index_.Erase(&lookup_key, &binfo);
   assert(ok);
   return binfo;
 }

utilities/write_batch_with_index/write_batch_with_index.cc

@@ -480,7 +480,8 @@ void WriteBatchWithIndex::Rep::AddNewEntry(uint32_t column_family_id) {
                           wb_data.size() - last_entry_offset);
   // Extract key
   Slice key;
-  bool success __attribute__((__unused__)) =
+  bool success __attribute__((__unused__));
+  success =
       ReadKeyFromWriteBatchEntry(&entry_ptr, &key, column_family_id != 0);
   assert(success);