[turbofan]: Add a context relaxer reducer

src/compiler/js-context-relaxation.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/frame-states.h"
+#include "src/compiler/js-context-relaxation.h"
+#include "src/compiler/js-operator.h"
+#include "src/compiler/node.h"
+#include "src/compiler/node-properties.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+Reduction JSContextRelaxation::Reduce(Node* node) {
+  switch (node->opcode()) {
+    case IrOpcode::kJSCallFunction:
+    case IrOpcode::kJSToNumber: {
+      Node* frame_state = NodeProperties::GetFrameStateInput(node, 0);
+      Node* outer_frame = frame_state;
+      Node* original_context = NodeProperties::GetContextInput(node);
+      Node* candidate_new_context = original_context;
+      do {
+        FrameStateInfo frame_state_info(
+            OpParameter<FrameStateInfo>(outer_frame->op()));
+        const FrameStateFunctionInfo* function_info =
+            frame_state_info.function_info();
+        if (function_info == nullptr ||
+            (function_info->context_calling_mode() ==
+             CALL_CHANGES_NATIVE_CONTEXT)) {
+          break;
+        }
+        candidate_new_context = outer_frame->InputAt(kFrameStateContextInput);
+        outer_frame = outer_frame->InputAt(kFrameStateOuterStateInput);
+      } while (outer_frame->opcode() == IrOpcode::kFrameState);
+
+      while (true) {
+        switch (candidate_new_context->opcode()) {
+          case IrOpcode::kParameter:
+          case IrOpcode::kJSCreateModuleContext:
+          case IrOpcode::kJSCreateScriptContext:
+            if (candidate_new_context != original_context) {
+              NodeProperties::ReplaceContextInput(node, candidate_new_context);
+              return Changed(node);
+            } else {
+              return NoChange();
+            }
+          case IrOpcode::kJSCreateCatchContext:
+          case IrOpcode::kJSCreateWithContext:
+          case IrOpcode::kJSCreateBlockContext:
+            candidate_new_context =
+                NodeProperties::GetContextInput(candidate_new_context);
+            break;
+          default:
+            return NoChange();
+        }
+      }
+    }
+    default:
+      break;
+  }
+  return NoChange();
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8