[turbofan]: Add a context relaxation Reducer

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 434 matching lines @@
       input_buffer_(nullptr),
       exit_controls_(local_zone),
       loop_assignment_analysis_(loop),
       state_values_cache_(jsgraph),
       liveness_analyzer_(static_cast<size_t>(info->scope()->num_stack_slots()),
                          local_zone),
       frame_state_function_info_(common()->CreateFrameStateFunctionInfo(
           FrameStateType::kJavaScriptFunction,
           info->num_parameters_including_this(),
           info->scope()->num_stack_slots(), info->shared_info())),
-      js_type_feedback_(js_type_feedback) {
+      js_type_feedback_(js_type_feedback),
+      relaxed_context_(nullptr) {
   InitializeAstVisitor(info->isolate(), local_zone);
 }
 
 
 Node* AstGraphBuilder::GetFunctionClosureForContext() {
   Scope* declaration_scope = current_scope()->DeclarationScope();
   if (declaration_scope->is_script_scope() ||
       declaration_scope->is_module_scope()) {
     // Contexts nested in the native context have a canonical empty function as
     // their closure, not the anonymous closure containing the global code.
@@ skipping 11 matching lines @@
     const Operator* op = common()->Parameter(
         Linkage::kJSFunctionCallClosureParamIndex, "%closure");
     Node* node = NewNode(op, graph()->start());
     function_closure_.set(node);
   }
   return function_closure_.get();
 }
 
 
 void AstGraphBuilder::CreateFunctionContext(bool constant_context) {
+  relaxed_context_ = NewOuterContextParam();
   function_context_.set(constant_context
                             ? jsgraph()->HeapConstant(info()->context())
-                            : NewOuterContextParam());
+                            : relaxed_context_);
 }
 
 
 Node* AstGraphBuilder::NewOuterContextParam() {
   // Parameter (arity + 1) is special for the outer context of the function
   const Operator* op =
       common()->Parameter(info()->num_parameters_including_this(), "%context");
   return NewNode(op, graph()->start());
 }
 
@@ skipping 3677 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