[turbofan] Disable usage of {maybe_assigned} variable flag.

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/ast/compile-time-value.h"
 #include "src/ast/scopes.h"
 #include "src/compilation-info.h"
 #include "src/compiler.h"
@@ skipping 3341 matching lines @@
           value = BuildThrowReferenceError(variable, bailout_id);
         } else if (value->opcode() == IrOpcode::kPhi) {
           value = BuildHoleCheckThenThrow(value, variable, value, bailout_id);
         }
       }
       return value;
     }
     case VariableLocation::CONTEXT: {
       // Context variable (potentially up the context chain).
       int depth = current_scope()->ContextChainLength(variable->scope());
-      bool immutable = variable->maybe_assigned() == kNotAssigned;
+      // TODO(mstarzinger): The {maybe_assigned} flag computed during variable
+      // resolution is highly inaccurate and cannot be trusted. We are only
+      // taking this information into account when asm.js compilation is used.
+      bool immutable = variable->maybe_assigned() == kNotAssigned &&
+                       info()->is_function_context_specializing();
       const Operator* op =
           javascript()->LoadContext(depth, variable->index(), immutable);
       Node* value = NewNode(op, current_context());
       // TODO(titzer): initialization checks are redundant for already
       // initialized immutable context loads, but only specialization knows.
       // Maybe specializer should be a parameter to the graph builder?
       if (variable->binding_needs_init()) {
         // Perform check for uninitialized let/const variables.
         value = BuildHoleCheckThenThrow(value, variable, value, bailout_id);
       }
@@ skipping 982 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