Bug 1563046: Move operator LogModule* out of line in debug builds. r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D36675

--HG--
extra : moz-landing-system : lando

mfbt/Attributes.h

@@ -92,6 +92,15 @@
 #  define MOZ_NEVER_INLINE /* no support */
 #endif
 
+/*
+ * MOZ_NEVER_INLINE_DEBUG is a macro which expands to MOZ_NEVER_INLINE
+ * in debug builds, and nothing in opt builds.
+ */
+#if defined(DEBUG)
+#  define MOZ_NEVER_INLINE_DEBUG MOZ_NEVER_INLINE
+#else
+#  define MOZ_NEVER_INLINE_DEBUG /* don't inline in opt builds */
+#endif
 /*
  * MOZ_NORETURN, specified at the start of a function declaration, indicates
  * that the given function does not return.  (The function definition does not

xpcom/base/Logging.h

@@ -168,7 +168,7 @@ class LazyLogModule final {
   explicit constexpr LazyLogModule(const char* aLogName)
       : mLogName(aLogName), mLog(nullptr) {}
 
-  operator LogModule*() {
+  MOZ_NEVER_INLINE_DEBUG operator LogModule*() {
     // NB: The use of an atomic makes the reading and assignment of mLog
     //     thread-safe. There is a small chance that mLog will be set more
     //     than once, but that's okay as it will be set to the same LogModule