Tweak ThreadLocal fast-path functions

Summary: [Folly] Tweak `ThreadLocal` fast-path functions. Mostly code golf.

Differential Revision: D9732836

fbshipit-source-id: fc48a7c067c6961413e6aa94106ae26f87d3d603

folly/ThreadLocal.h

@@ -67,13 +67,8 @@ class ThreadLocal {
       : constructor_(std::forward<F>(constructor)) {}
 
   T* get() const {
-    T* const ptr = tlp_.get();
-    if (LIKELY(ptr != nullptr)) {
-      return ptr;
-    }
-
-    // separated new item creation out to speed up the fast path.
-    return makeTlp();
+    auto const ptr = tlp_.get();
+    return FOLLY_LIKELY(!!ptr) ? ptr : makeTlp();
   }
 
   T* operator->() const {

folly/detail/ThreadLocalDetail.h

@@ -434,20 +434,19 @@ struct StaticMeta final : StaticMetaBase {
   }
 
   FOLLY_ALWAYS_INLINE static ElementWrapper& get(EntryID* ent) {
+    // Eliminate as many branches and as much extra code as possible in the
+    // cached fast path, leaving only one branch here and one indirection below.
     uint32_t id = ent->getOrInvalid();
 #ifdef FOLLY_TLD_USE_FOLLY_TLS
     static FOLLY_TLS ThreadEntry* threadEntry{};
     static FOLLY_TLS size_t capacity{};
-    // Eliminate as many branches and as much extra code as possible in the
-    // cached fast path, leaving only one branch here and one indirection below.
-    if (UNLIKELY(capacity <= id)) {
-      getSlowReserveAndCache(ent, id, threadEntry, capacity);
-    }
 #else
     ThreadEntry* threadEntry{};
     size_t capacity{};
-    getSlowReserveAndCache(ent, id, threadEntry, capacity);
 #endif
+    if (FOLLY_UNLIKELY(capacity <= id)) {
+      getSlowReserveAndCache(ent, id, threadEntry, capacity);
+    }
     return threadEntry->elements[id];
   }