[turbofan] Use Start as sentinel for frame states.

src/compiler/verifier.cc

 // Copyright 2014 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/verifier.h"
 
 #include <algorithm>
 #include <deque>
 #include <queue>
 #include <sstream>
@@ skipping 100 matching lines @@
 
   // Verify number of inputs matches up.
   int input_count = value_count + context_count + frame_state_count +
                     effect_count + control_count;
   CHECK_EQ(input_count, node->InputCount());
 
   // Verify that frame state has been inserted for the nodes that need it.
   for (int i = 0; i < frame_state_count; i++) {
     Node* frame_state = NodeProperties::GetFrameStateInput(node, i);
     CHECK(frame_state->opcode() == IrOpcode::kFrameState ||
-          // kFrameState uses undefined as a sentinel.
+          // kFrameState uses Start as a sentinel.
           (node->opcode() == IrOpcode::kFrameState &&
-           frame_state->opcode() == IrOpcode::kHeapConstant));
+           frame_state->opcode() == IrOpcode::kStart));
     CHECK(IsDefUseChainLinkPresent(frame_state, node));
     CHECK(IsUseDefChainLinkPresent(frame_state, node));
   }
 
   // Verify all value inputs actually produce a value.
   for (int i = 0; i < value_count; ++i) {
     Node* value = NodeProperties::GetValueInput(node, i);
     CHECK(value->op()->ValueOutputCount() > 0);
     CHECK(IsDefUseChainLinkPresent(value, node));
     CHECK(IsUseDefChainLinkPresent(value, node));
@@ skipping 978 matching lines @@
     // Check inputs for all nodes in the block.
     for (size_t i = 0; i < block->NodeCount(); i++) {
       Node* node = block->NodeAt(i);
       CheckInputsDominate(schedule, block, node, static_cast<int>(i) - 1);
     }
   }
 }
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8