[turbofan] Don't eliminate FinishRegion nodes.

src/compiler/typed-optimization.cc

 // Copyright 2016 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/typed-optimization.h"
 
 #include "src/compilation-dependencies.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/node-properties.h"
 #include "src/compiler/simplified-operator.h"
@@ skipping 15 matching lines @@
       false_type_(Type::Constant(factory()->false_value(), graph()->zone())),
       type_cache_(TypeCache::Get()) {}
 
 TypedOptimization::~TypedOptimization() {}
 
 Reduction TypedOptimization::Reduce(Node* node) {
   // Check if the output type is a singleton.  In that case we already know the
   // result value and can simply replace the node if it's eliminable.
   if (!NodeProperties::IsConstant(node) && NodeProperties::IsTyped(node) &&
       node->op()->HasProperty(Operator::kEliminatable)) {
+    // TODO(v8:5303): We must not eliminate FinishRegion here. This special
+    // case can be removed once we have separate operators for value and
+    // effect regions.
+    if (node->opcode() == IrOpcode::kFinishRegion) return NoChange();
     // We can only constant-fold nodes here, that are known to not cause any
     // side-effect, may it be a JavaScript observable side-effect or a possible
     // eager deoptimization exit (i.e. {node} has an operator that doesn't have
     // the Operator::kNoDeopt property).
     Type* upper = NodeProperties::GetType(node);
     if (upper->IsInhabited()) {
       if (upper->IsConstant()) {
         Node* replacement = jsgraph()->Constant(upper->AsConstant()->Value());
         ReplaceWithValue(node, replacement);
         return Changed(replacement);
@@ skipping 202 matching lines @@
 
 Isolate* TypedOptimization::isolate() const { return jsgraph()->isolate(); }
 
 SimplifiedOperatorBuilder* TypedOptimization::simplified() const {
   return jsgraph()->simplified();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8