Bug 577764 - TM: avoid a dead guard at the end of loop fragments. r=dvander.

js/src/jstracer.cpp

@@ -4717,17 +4717,17 @@ TraceRecorder::closeLoop(SlotMap& slotMap, VMSideExit* exit)
         }
     } else {
         exit->exitType = LOOP_EXIT;
+        exit->target = tree;
         debug_only_printf(LC_TMTreeVis, "TREEVIS CHANGEEXIT EXIT=%p TYPE=%s\n", (void*)exit,
                           getExitName(LOOP_EXIT));
 
         JS_ASSERT((fragment == fragment->root) == !!loopLabel);
         if (loopLabel) {
             lir->insBranch(LIR_j, NULL, loopLabel);
-            lir->ins1(LIR_livep, lirbuf->state);
+            fragment->lastIns = lir->ins1(LIR_livep, lirbuf->state);
+        } else {
+            fragment->lastIns = lir->insGuard(LIR_x, NULL, createGuardRecord(exit));
         }
-
-        exit->target = tree;
-        fragment->lastIns = lir->insGuard(LIR_x, NULL, createGuardRecord(exit));
     }
 
     CHECK_STATUS_A(compile());