[Parser] Enable new parser validation only in 'assertions' builds

Author: rintaro

lib/Frontend/CompilerInvocation.cpp

@@ -1691,7 +1691,7 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.DisableDynamicActorIsolation |=
       Args.hasArg(OPT_disable_dynamic_actor_isolation);
 
-#if SWIFT_ENABLE_EXPERIMENTAL_PARSER_VALIDATION
+#if !defined(NDEBUG) && SWIFT_ENABLE_EXPERIMENTAL_PARSER_VALIDATION
   /// Enable round trip parsing via the new swift parser unless it is disabled
   /// explicitly. The new Swift parser can have mismatches with C++ parser -
   /// rdar://118013482 Use this flag to disable round trip through the new