[turbofan] second attempt to fix second divergence in escape analysis

src/compiler/escape-analysis.cc

 // Copyright 2015 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/escape-analysis.h"
 
 #include <limits>
 
 #include "src/base/flags.h"
 #include "src/bootstrapper.h"
@@ skipping 183 matching lines @@
   bool AllFieldsClear() {
     for (size_t i = 0; i < fields_.size(); ++i) {
       if (fields_[i] != nullptr) {
         return false;
       }
     }
     return true;
   }
   bool UpdateFrom(const VirtualObject& other);
   bool MergeFrom(MergeCache* cache, Node* at, Graph* graph,
-                 CommonOperatorBuilder* common);
+                 CommonOperatorBuilder* common, bool initialMerge);
   void SetObjectState(Node* node) { object_state_ = node; }
   Node* GetObjectState() const { return object_state_; }
   bool IsCopyRequired() const { return status_ & kCopyRequired; }
   void SetCopyRequired() { status_ |= kCopyRequired; }
   bool NeedCopyForModification() {
     if (!IsCopyRequired() || !IsInitialized()) {
       return false;
     }
     return true;
   }
@@ skipping 257 matching lines @@
       if (old != cache->fields()[n]) {
         changed = true;
         NodeProperties::ReplaceValueInput(rep, cache->fields()[n], n);
       }
     }
   }
   return changed;
 }
 
 bool VirtualObject::MergeFrom(MergeCache* cache, Node* at, Graph* graph,
-                              CommonOperatorBuilder* common) {
+                              CommonOperatorBuilder* common,
+                              bool initialMerge) {
   DCHECK(at->opcode() == IrOpcode::kEffectPhi ||
          at->opcode() == IrOpcode::kPhi);
   bool changed = false;
   for (size_t i = 0; i < field_count(); ++i) {
+    if (!initialMerge && GetField(i) == nullptr) continue;
     Node* field = cache->GetFields(i);
     if (field && !IsCreatedPhi(i)) {
       changed = changed || GetField(i) != field;
       SetField(i, field);
       TRACE("    Field %zu agree on rep #%d\n", i, field->id());
     } else {
       size_t arity = at->opcode() == IrOpcode::kEffectPhi
                          ? at->op()->EffectInputCount()
                          : at->op()->ValueInputCount();
       if (cache->fields().size() == arity) {
@@ skipping 22 matching lines @@
     for (VirtualState* state : cache->states()) {
       if (VirtualObject* obj = state->VirtualObjectFromAlias(alias)) {
         cache->objects().push_back(obj);
         if (mergeObject == obj) {
           copy_merge_object = true;
         }
         fields = std::min(obj->field_count(), fields);
       }
     }
     if (cache->objects().size() == cache->states().size()) {
+      bool initialMerge = false;
       if (!mergeObject) {
+        initialMerge = true;
         VirtualObject* obj = new (zone)
             VirtualObject(cache->objects().front()->id(), this, zone, fields,
                           cache->objects().front()->IsInitialized());
         SetVirtualObject(alias, obj);
         mergeObject = obj;
         changed = true;
       } else if (copy_merge_object) {
         VirtualObject* obj = new (zone) VirtualObject(this, *mergeObject);
         SetVirtualObject(alias, obj);
         mergeObject = obj;
         changed = true;
       } else {
         changed = mergeObject->ResizeFields(fields) || changed;
       }
 #ifdef DEBUG
       if (FLAG_trace_turbo_escape) {
         PrintF("  Alias @%d, merging into %p virtual objects", alias,
                static_cast<void*>(mergeObject));
         for (size_t i = 0; i < cache->objects().size(); i++) {
           PrintF(" %p", static_cast<void*>(cache->objects()[i]));
         }
         PrintF("\n");
       }
 #endif  // DEBUG
-      changed = mergeObject->MergeFrom(cache, at, graph, common) || changed;
+      changed =
+          mergeObject->MergeFrom(cache, at, graph, common, initialMerge) ||
+          changed;
     } else {
       if (mergeObject) {
         TRACE("  Alias %d, virtual object removed\n", alias);
         changed = true;
       }
       SetVirtualObject(alias, nullptr);
     }
   }
   return changed;
 }
@@ skipping 1141 matching lines @@
     }
   }
   return false;
 }
 
 Graph* EscapeAnalysis::graph() const { return status_analysis_->graph(); }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8