Report parent of stitched trace.

Thanks to Nick Zavaritsky.

src/jit/dump.lua

@@ -556,7 +556,7 @@ local function dump_trace(what, tr, func, pc, otr, oex)
   if what == "start" then
     if dumpmode.H then out:write('<pre class="ljdump">\n') end
     out:write("---- TRACE ", tr, " ", what)
-    if otr then out:write(" ", otr, "/", oex) end
+    if otr then out:write(" ", otr, "/", oex == -1 and "stitch" or oex) end
     out:write(" ", fmtfunc(func, pc), "\n")
   elseif what == "stop" or what == "abort" then
     out:write("---- TRACE ", tr, " ", what)

src/jit/v.lua

@@ -99,7 +99,7 @@ end
 local function dump_trace(what, tr, func, pc, otr, oex)
   if what == "start" then
     startloc = fmtfunc(func, pc)
-    startex = otr and "("..otr.."/"..oex..") " or ""
+    startex = otr and "("..otr.."/"..(oex == -1 and "stitch" or oex)..") " or ""
   else
     if what == "abort" then
       local loc = fmtfunc(func, pc)

src/lj_trace.c

@@ -446,6 +446,12 @@ static void trace_start(jit_State *J)
     if (J->parent) {
       setintV(L->top++, J->parent);
       setintV(L->top++, J->exitno);
+    } else {
+      BCOp op = bc_op(*J->pc);
+      if (op == BC_CALLM || op == BC_CALL || op == BC_ITERC) {
+	setintV(L->top++, J->exitno);  /* Parent of stitched trace. */
+	setintV(L->top++, -1);
+      }
     }
   );
   lj_record_setup(J);