Overload new[] to properly align LRUCacheShard

Summary:
Also verify it fixes gcc7 compile failure #2672 (see also #2699)
Closes https://github.com/facebook/rocksdb/pull/2732

Differential Revision: D5620348

Pulled By: yiwu-arbug

fbshipit-source-id: 87db657ab734f23b1bfaaa9db9b9956d10eaef59

Makefile

@@ -259,19 +259,6 @@ default: all
 WARNING_FLAGS = -W -Wextra -Wall -Wsign-compare -Wshadow \
   -Wno-unused-parameter
 
-CCVERSION = $(shell $(CXX) -dumpversion)
-CCNAME = $(shell $(CXX) --version | awk 'NR==1' | cut -f1 -d " ")
-
-ifeq ($(CCNAME), clang)
-ifeq ($(CCVERSION), 4*)
-	CXXFLAGS += -faligned-new
-endif
-else
-ifeq ($(CCVERSION), 7)
-	CXXFLAGS += -faligned-new
-endif
-endif
-
 ifndef DISABLE_WARNING_AS_ERROR
 	WARNING_FLAGS += -Werror
 endif

cache/lru_cache.cc

@@ -234,11 +234,19 @@ void LRUCacheShard::EvictFromLRU(size_t charge,
 }
 
 void* LRUCacheShard::operator new(size_t size) {
-  return rocksdb::port::cacheline_aligned_alloc(size);
+  return port::cacheline_aligned_alloc(size);
+}
+
+void* LRUCacheShard::operator new[](size_t size) {
+  return port::cacheline_aligned_alloc(size);
 }
 
 void LRUCacheShard::operator delete(void *memblock) {
-  rocksdb::port::cacheline_aligned_free(memblock);
+  port::cacheline_aligned_free(memblock);
+}
+
+void LRUCacheShard::operator delete[](void* memblock) {
+  port::cacheline_aligned_free(memblock);
 }
 
 void LRUCacheShard::SetCapacity(size_t capacity) {

cache/lru_cache.h

@@ -205,8 +205,12 @@ class ALIGN_AS(CACHE_LINE_SIZE) LRUCacheShard : public CacheShard {
   // Overloading to aligned it to cache line size
   void* operator new(size_t);
 
+  void* operator new[](size_t);
+
   void operator delete(void *);
 
+  void operator delete[](void*);
+
  private:
   void LRU_Remove(LRUHandle* e);
   void LRU_Insert(LRUHandle* e);