tblgen: Assert that InstRWs doesn't grows when we don't expect it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183690 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/CodeGenSchedule.cpp b/utils/TableGen/CodeGenSchedule.cpp
index 503dfc2..8015e34 100644
--- a/utils/TableGen/CodeGenSchedule.cpp
+++ b/utils/TableGen/CodeGenSchedule.cpp
@@ -891,6 +891,7 @@
 /// Infer classes from per-processor InstReadWrite definitions.
 void CodeGenSchedModels::inferFromInstRWs(unsigned SCIdx) {
   for (unsigned I = 0, E = SchedClasses[SCIdx].InstRWs.size(); I != E; ++I) {
+    assert(SchedClasses[SCIdx].InstRWs.size() == E && "InstrRWs was mutated!");
     Record *Rec = SchedClasses[SCIdx].InstRWs[I];
     const RecVec *InstDefs = Sets.expand(Rec);
     RecIter II = InstDefs->begin(), IE = InstDefs->end();