[turbofan] put spill slot reuse behind a flag

src/compiler/graph-visualizer.cc

Index: src/compiler/graph-visualizer.cc
diff --git a/src/compiler/graph-visualizer.cc b/src/compiler/graph-visualizer.cc
index 40b182a34c881352cef2b3242db5b1860e83e6a6..c9be0ac5ac2450f0f2bb2cde4a442aa0a264c11f 100644
--- a/src/compiler/graph-visualizer.cc
+++ b/src/compiler/graph-visualizer.cc
@@ -724,7 +724,8 @@ void GraphC1Visualizer::PrintLiveRange(LiveRange* range, const char* type) {
       }
     } else if (range->IsSpilled()) {
       int index = -1;
-      if (range->TopLevel()->GetSpillRange()->id() != -1) {
+      if (range->TopLevel()->GetSpillRange() != nullptr &&
+          range->TopLevel()->GetSpillRange()->id() != -1) {
         index = range->TopLevel()->GetSpillRange()->id();
       } else {
         index = range->TopLevel()->GetSpillOperand()->index();