[turbofan] Optimized lowering of DYNAMIC_LOCAL lookup slot loads.

src/compiler/ast-graph-builder.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/ast-graph-builder.h"
 
 #include "src/compiler.h"
 #include "src/compiler/ast-loop-assignment-analyzer.h"
 #include "src/compiler/control-builders.h"
 #include "src/compiler/js-type-feedback.h"
@@ skipping 2754 matching lines @@
   }
   return check_depths.ToIntegral();
 }
 
 
 uint32_t AstGraphBuilder::ComputeBitsetForDynamicContext(Variable* variable) {
   DCHECK_EQ(DYNAMIC_LOCAL, variable->mode());
   EnumSet<int, uint32_t> check_depths;
   for (Scope* s = current_scope(); s != nullptr; s = s->outer_scope()) {
     if (s->num_heap_slots() <= 0) continue;
-    if (!s->calls_sloppy_eval()) continue;
+    if (!s->calls_sloppy_eval() && s != variable->scope()) continue;
     int depth = current_scope()->ContextChainLength(s);
     if (depth > DynamicContextAccess::kMaxCheckDepth) {
       return DynamicContextAccess::kFullCheckRequired;
     }
     check_depths.Add(depth);
     if (s == variable->scope()) break;
   }
   return check_depths.ToIntegral();
 }
 
@@ skipping 247 matching lines @@
         states.AddToNode(value, bailout_id, combine);
       } else if (mode == DYNAMIC_LOCAL) {
         Variable* local = variable->local_if_not_shadowed();
         DCHECK(local->location() == Variable::CONTEXT);  // Must be context.
         int depth = current_scope()->ContextChainLength(local->scope());
         uint32_t check_bitset = ComputeBitsetForDynamicContext(variable);
         const Operator* op = javascript()->LoadDynamicContext(
             name, check_bitset, depth, local->index());
         value = NewNode(op, current_context());
         PrepareFrameState(value, bailout_id, combine);
-        // TODO(mstarzinger): Hole checks are missing here when optimized.
+        VariableMode local_mode = local->mode();
+        if (local_mode == CONST_LEGACY) {
+          // Perform check for uninitialized legacy const variables.
+          Node* undefined = jsgraph()->UndefinedConstant();
+          value = BuildHoleCheckSilent(value, undefined, value);
+        } else if (local_mode == LET || local_mode == CONST) {
+          // Perform check for uninitialized let/const variables.
+          value = BuildHoleCheckThrow(value, local, value, bailout_id);
+        }
       } else if (mode == DYNAMIC) {
         uint32_t check_bitset = DynamicGlobalAccess::kFullCheckRequired;
         const Operator* op = javascript()->LoadDynamicGlobal(
             name, check_bitset, feedback, contextual_mode);
         value = NewNode(op, current_context());
         states.AddToNode(value, bailout_id, combine);
       }
       return value;
     }
   }
@@ skipping 725 matching lines @@
     // Phi does not exist yet, introduce one.
     value = NewPhi(inputs, value, control);
     value->ReplaceInput(inputs - 1, other);
   }
   return value;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8