[turbofan] Remove untested no-deoptimization code path from JSGlobalObjectSpecialization.

src/compiler/js-global-object-specialization.cc

Index: src/compiler/js-global-object-specialization.cc
diff --git a/src/compiler/js-global-object-specialization.cc b/src/compiler/js-global-object-specialization.cc
index e6f01b3efb3fc5e094b9e6693c5ea63bf4705bd3..0f4f75d98f7e55667546eab2c7acff2e3bcf17fa 100644
--- a/src/compiler/js-global-object-specialization.cc
+++ b/src/compiler/js-global-object-specialization.cc
@@ -27,11 +27,10 @@ struct JSGlobalObjectSpecialization::ScriptContextTableLookupResult {
 
 
 JSGlobalObjectSpecialization::JSGlobalObjectSpecialization(
-    Editor* editor, JSGraph* jsgraph, Flags flags,
+    Editor* editor, JSGraph* jsgraph,
     MaybeHandle<Context> native_context, CompilationDependencies* dependencies)
     : AdvancedReducer(editor),
       jsgraph_(jsgraph),
-      flags_(flags),
       native_context_(native_context),
       dependencies_(dependencies),
       type_cache_(TypeCache::Get()) {}
@@ -49,7 +48,6 @@ Reduction JSGlobalObjectSpecialization::Reduce(Node* node) {
   return NoChange();
 }
 
-
 Reduction JSGlobalObjectSpecialization::ReduceJSLoadGlobal(Node* node) {
   DCHECK_EQ(IrOpcode::kJSLoadGlobal, node->opcode());
   Handle<Name> name = LoadGlobalParametersOf(node->op()).name();
@@ -88,47 +86,36 @@ Reduction JSGlobalObjectSpecialization::ReduceJSLoadGlobal(Node* node) {
     return Replace(value);
   }
 
-  // Load from non-configurable, data property on the global can be lowered to
-  // a field load, even without deoptimization, because the property cannot be
-  // deleted or reconfigured to an accessor/interceptor property.  Yet, if
-  // deoptimization support is available, we can constant-fold certain global
-  // properties or at least lower them to field loads annotated with more
-  // precise type feedback.
-  Type* property_cell_value_type = Type::Tagged();
-  if (flags() & kDeoptimizationEnabled) {
-    // Record a code dependency on the cell if we can benefit from the
-    // additional feedback, or the global property is configurable (i.e.
-    // can be deleted or reconfigured to an accessor property).
-    if (property_details.cell_type() != PropertyCellType::kMutable ||
-        property_details.IsConfigurable()) {
-      dependencies()->AssumePropertyCell(property_cell);
-    }
+  // Record a code dependency on the cell if we can benefit from the
+  // additional feedback, or the global property is configurable (i.e.
+  // can be deleted or reconfigured to an accessor property).
+  if (property_details.cell_type() != PropertyCellType::kMutable ||
+      property_details.IsConfigurable()) {
+    dependencies()->AssumePropertyCell(property_cell);
+  }
 
-    // Load from constant/undefined global property can be constant-folded.
-    if ((property_details.cell_type() == PropertyCellType::kConstant ||
-         property_details.cell_type() == PropertyCellType::kUndefined)) {
-      Node* value = jsgraph()->Constant(property_cell_value);
-      ReplaceWithValue(node, value);
-      return Replace(value);
-    }
+  // Load from constant/undefined global property can be constant-folded.
+  if (property_details.cell_type() == PropertyCellType::kConstant ||
+      property_details.cell_type() == PropertyCellType::kUndefined) {
+    Node* value = jsgraph()->Constant(property_cell_value);
+    ReplaceWithValue(node, value);
+    return Replace(value);
+  }
 
-    // Load from constant type cell can benefit from type feedback.
-    if (property_details.cell_type() == PropertyCellType::kConstantType) {
-      // Compute proper type based on the current value in the cell.
-      if (property_cell_value->IsSmi()) {
-        property_cell_value_type = type_cache_.kSmi;
-      } else if (property_cell_value->IsNumber()) {
-        property_cell_value_type = type_cache_.kHeapNumber;
-      } else {
-        Handle<Map> property_cell_value_map(
-            Handle<HeapObject>::cast(property_cell_value)->map(), isolate());
-        property_cell_value_type =
-            Type::Class(property_cell_value_map, graph()->zone());
-      }
+  // Load from constant type cell can benefit from type feedback.
+  Type* property_cell_value_type = Type::Tagged();
+  if (property_details.cell_type() == PropertyCellType::kConstantType) {
+    // Compute proper type based on the current value in the cell.
+    if (property_cell_value->IsSmi()) {
+      property_cell_value_type = type_cache_.kSmi;
+    } else if (property_cell_value->IsNumber()) {
+      property_cell_value_type = type_cache_.kHeapNumber;
+    } else {
+      Handle<Map> property_cell_value_map(
+          Handle<HeapObject>::cast(property_cell_value)->map(), isolate());
+      property_cell_value_type =
+          Type::Class(property_cell_value_map, graph()->zone());
     }
-  } else if (property_details.IsConfigurable()) {
-    // Access to configurable global properties requires deoptimization support.
-    return NoChange();
   }
   Node* value = effect = graph()->NewNode(
       simplified()->LoadField(
@@ -178,9 +165,8 @@ Reduction JSGlobalObjectSpecialization::ReduceJSStoreGlobal(Node* node) {
       return NoChange();
     }
     case PropertyCellType::kConstant: {
-      // Store to constant property cell requires deoptimization support,
-      // because we might even need to eager deoptimize for mismatch.
-      if (!(flags() & kDeoptimizationEnabled)) return NoChange();
+      // Record a code dependency on the cell, and just deoptimize if the new
+      // value doesn't match the previous value stored inside the cell.
       dependencies()->AssumePropertyCell(property_cell);
       Node* check =
           graph()->NewNode(simplified()->ReferenceEqual(Type::Tagged()), value,
@@ -197,9 +183,8 @@ Reduction JSGlobalObjectSpecialization::ReduceJSStoreGlobal(Node* node) {
       break;
     }
     case PropertyCellType::kConstantType: {
-      // Store to constant-type property cell requires deoptimization support,
-      // because we might even need to eager deoptimize for mismatch.
-      if (!(flags() & kDeoptimizationEnabled)) return NoChange();
+      // Record a code dependency on the cell, and just deoptimize if the new
+      // values' type doesn't match the type of the previous value in the cell.
       dependencies()->AssumePropertyCell(property_cell);
       Node* check = graph()->NewNode(simplified()->ObjectIsSmi(), value);
       Type* property_cell_value_type = Type::TaggedSigned();
@@ -243,13 +228,11 @@ Reduction JSGlobalObjectSpecialization::ReduceJSStoreGlobal(Node* node) {
     }
     case PropertyCellType::kMutable: {
       // Store to non-configurable, data property on the global can be lowered
-      // to a field store, even without deoptimization, because the property
-      // cannot be deleted or reconfigured to an accessor/interceptor property.
+      // to a field store, even without recording a code dependency on the cell,
+      // because the property cannot be deleted or reconfigured to an accessor
+      // or interceptor property.
       if (property_details.IsConfigurable()) {
-        // With deoptimization support, we can lower stores even to configurable
-        // data properties on the global object, by adding a code dependency on
-        // the cell.
-        if (!(flags() & kDeoptimizationEnabled)) return NoChange();
+        // Protect lowering by recording a code dependency on the cell.
         dependencies()->AssumePropertyCell(property_cell);
       }
       effect = graph()->NewNode(