Outline several fbstring/malloc functions

Summary: Outline all the non-trivial constructor and the destructor, `assign()`, and `append()` to reduce code size. The fast path of copy, and moves, are instead still inlined.

Reviewed By: philippv

Differential Revision: D3896612

fbshipit-source-id: 25050d4ba28d25da226a7bc49d5b542947d0c512

folly/Malloc.h

@@ -111,6 +111,7 @@ __attribute__((__weak__));
 #include <cstdlib>
 #include <cstring>
 
+#include <atomic>
 #include <new>
 
 #ifdef _LIBSTDCXX_FBSTRING
@@ -121,17 +122,21 @@ namespace folly {
 #endif
 
 // Cannot depend on Portability.h when _LIBSTDCXX_FBSTRING.
-// Disabled for nvcc because it fails on attributes on lambdas.
-#if defined(__GNUC__) && !defined(__NVCC__)
+#if defined(__GNUC__)
 #define FOLLY_MALLOC_NOINLINE __attribute__((__noinline__))
+// This is for checked malloc-like functions (returns non-null pointer
+// which cannot alias any outstanding pointer).
+#define FOLLY_MALLOC_CHECKED_MALLOC                     \
+  __attribute__((__returns_nonnull__, __malloc__))
 #else
 #define FOLLY_MALLOC_NOINLINE
+#define FOLLY_MALLOC_CHECKED_MALLOC
 #endif
 
 /**
  * Determine if we are using jemalloc or not.
  */
-inline bool usingJEMalloc() noexcept {
+FOLLY_MALLOC_NOINLINE inline bool usingJEMalloc() noexcept {
   // Checking for rallocx != NULL is not sufficient; we may be in a dlopen()ed
   // module that depends on libjemalloc, so rallocx is resolved, but the main
   // program might be using a different memory allocator.
@@ -140,7 +145,7 @@ inline bool usingJEMalloc() noexcept {
   // per-thread counter of allocated memory increases. This makes me
   // feel dirty inside. Also note that this requires jemalloc to have
   // been compiled with --enable-stats.
-  static const bool result = [] () FOLLY_MALLOC_NOINLINE noexcept {
+  static const bool result = [] () noexcept {
     // Some platforms (*cough* OSX *cough*) require weak symbol checks to be
     // in the form if (mallctl != nullptr). Not if (mallctl) or if (!mallctl)
     // (!!). http://goo.gl/xpmctm
@@ -235,7 +240,8 @@ inline void* checkedRealloc(void* ptr, size_t size) {
  * routine just tries to call realloc() (thus benefitting of potential
  * copy-free coalescing) unless there's too much slack memory.
  */
-inline void* smartRealloc(void* p,
+FOLLY_MALLOC_CHECKED_MALLOC FOLLY_MALLOC_NOINLINE inline void* smartRealloc(
+    void* p,
     const size_t currentSize,
     const size_t currentCapacity,
     const size_t newCapacity) {