Specialize to ffid for non-monomorphic builtins.

src/lj_ir.h

@@ -194,6 +194,7 @@ IRFPMDEF(FPMENUM)
   _(STR_LEN,	offsetof(GCstr, len)) \
   _(FUNC_ENV,	offsetof(GCfunc, l.env)) \
   _(FUNC_PC,	offsetof(GCfunc, l.pc)) \
+  _(FUNC_FFID,	offsetof(GCfunc, l.ffid)) \
   _(THREAD_ENV,	offsetof(lua_State, env)) \
   _(TAB_META,	offsetof(GCtab, metatable)) \
   _(TAB_ARRAY,	offsetof(GCtab, array)) \

src/lj_record.c

@@ -648,7 +648,10 @@ static TRef rec_call_specialize(jit_State *J, GCfunc *fn, TRef tr)
     case FF_coroutine_wrap_aux:
     case FF_string_gmatch_aux:
       /* NYI: io_file_iter doesn't have an ffid, yet. */
-      /* NYI: specialize to ffid? Not strictly necessary, trace will stop. */
+      {  /* Specialize to the ffid. */
+	TRef trid = emitir(IRT(IR_FLOAD, IRT_U8), tr, IRFL_FUNC_FFID);
+	emitir(IRTG(IR_EQ, IRT_INT), trid, lj_ir_kint(J, fn->c.ffid));
+      }
       return tr;
     default:
       /* NYI: don't specialize to non-monomorphic C functions. */