[turbofan]: Add a context relaxation Reducer

src/compiler/ast-graph-builder.cc

Index: src/compiler/ast-graph-builder.cc
diff --git a/src/compiler/ast-graph-builder.cc b/src/compiler/ast-graph-builder.cc
index 0abc9918df6595454e83f095732f71049ddc4088..1c8456d11e961e6091f14040c9011c5dcc94fbdb 100644
--- a/src/compiler/ast-graph-builder.cc
+++ b/src/compiler/ast-graph-builder.cc
@@ -452,7 +452,8 @@ AstGraphBuilder::AstGraphBuilder(Zone* local_zone, CompilationInfo* info,
           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);
 }
 
@@ -484,9 +485,10 @@ Node* AstGraphBuilder::GetFunctionClosure() {
 
 
 void AstGraphBuilder::CreateFunctionContext(bool constant_context) {
+  relaxed_context_ = NewOuterContextParam();
   function_context_.set(constant_context
                             ? jsgraph()->HeapConstant(info()->context())
-                            : NewOuterContextParam());
+                            : relaxed_context_);
 }