[turbofan] Allow ReplaceWithValue to kill control.

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 176 matching lines @@
     case IrOpcode::kEnd:
       // End has no outputs.
       CHECK(node->op()->ValueOutputCount() == 0);
       CHECK(node->op()->EffectOutputCount() == 0);
       CHECK(node->op()->ControlOutputCount() == 0);
       // Type is empty.
       CheckNotTyped(node);
       break;
     case IrOpcode::kDead:
       // Dead is never connected to the graph.
-      UNREACHABLE();
+      // TODO(mstarzinger): Make the GraphReducer immediately perform control
+      // reduction in case control is killed. This will prevent {Dead} from
+      // being reachable after a phase finished. Then re-enable below assert.
+      // UNREACHABLE();
+      break;
     case IrOpcode::kBranch: {
       // Branch uses are IfTrue and IfFalse.
       int count_true = 0, count_false = 0;
       for (auto use : node->uses()) {
         CHECK(use->opcode() == IrOpcode::kIfTrue ||
               use->opcode() == IrOpcode::kIfFalse);
         if (use->opcode() == IrOpcode::kIfTrue) ++count_true;
         if (use->opcode() == IrOpcode::kIfFalse) ++count_false;
       }
       CHECK_EQ(1, count_true);
@@ skipping 918 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