[turbofan] Add general support for sp-based frame access

src/compiler/frame-access-state.h

Index: src/compiler/frame-access-state.h
diff --git a/src/compiler/frame-access-state.h b/src/compiler/frame-access-state.h
new file mode 100644
index 0000000000000000000000000000000000000000..d6138277132cbd3f60b847dc07fcd096fae507e7
--- /dev/null
+++ b/src/compiler/frame-access-state.h
@@ -0,0 +1,44 @@
+// Copyright 2015 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.
+
+#ifndef V8_COMPILER_FRAME_ACCESS_STATE_H_
+#define V8_COMPILER_FRAME_ACCESS_STATE_H_
+
+#include "src/compiler/frame.h"
+
+class Frame;
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+class FrameAccessState : public ZoneObject {

[titzer, 2015/11/23 20:00:54]

What about moving this class into frame.h? The two are so tightly coupled that
they almost always would be used together, I guess.

[danno, 2015/11/24 12:02:00]

Done.

+ public:
+  explicit FrameAccessState(Frame* const frame)
+      : frame_(frame), access_frame_with_fp_(false), sp_delta_(0) {
+    UseDefaultFrameAccess();
+  }
+
+  Frame* const frame() const { return frame_; }
+
+  int sp_delta() const { return sp_delta_; }
+  void ClearSPDelta() { sp_delta_ = 0; }
+  void IncreaseSPDelta(int amount) { sp_delta_ += amount; }
+
+  bool access_frame_with_fp() const { return access_frame_with_fp_; }
+  void UseDefaultFrameAccess();
+  void UseFPToAccessFrame() { access_frame_with_fp_ = true; }

[titzer, 2015/11/23 20:00:54]

The name of these methods doesn't really indicate that they alter state. Maybe
SetFrameAccessToFP(bool)?

[danno, 2015/11/24 12:02:00]

Done.

+  void UseSPToAccessFrame() { access_frame_with_fp_ = false; }
+
+ private:
+  Frame* const frame_;
+  bool access_frame_with_fp_;
+  int sp_delta_;
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_FRAME_ACCESS_STATE_H_