[turbofan] put spill slot reuse behind a flag

src/compiler/graph-visualizer.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/graph-visualizer.h"
 
 #include <sstream>
 #include <string>
 
 #include "src/code-stubs.h"
@@ skipping 706 matching lines @@
       int assigned_reg = op->index();
       if (op->IsDoubleRegister()) {
         os_ << " \"" << DoubleRegister::AllocationIndexToString(assigned_reg)
             << "\"";
       } else {
         DCHECK(op->IsRegister());
         os_ << " \"" << Register::AllocationIndexToString(assigned_reg) << "\"";
       }
     } 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();
       }
       if (range->TopLevel()->Kind() == DOUBLE_REGISTERS) {
         os_ << " \"double_stack:" << index << "\"";
       } else if (range->TopLevel()->Kind() == GENERAL_REGISTERS) {
         os_ << " \"stack:" << index << "\"";
       } else {
         os_ << " \"const(nostack):" << index << "\"";
@@ skipping 47 matching lines @@
 
 
 std::ostream& operator<<(std::ostream& os, const AsC1VAllocator& ac) {
   Zone tmp_zone(ac.allocator_->code()->zone()->isolate());
   GraphC1Visualizer(os, &tmp_zone).PrintAllocator(ac.phase_, ac.allocator_);
   return os;
 }
 }
 }
 }  // namespace v8::internal::compiler