[turbofan] CodeGenerator: Frame setup refactoring

src/compiler/frame.h

 // 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.
 
 #ifndef V8_COMPILER_FRAME_H_
 #define V8_COMPILER_FRAME_H_
 
 #include "src/bit-vector.h"
 #include "src/frames.h"
 
@@ skipping 64 matching lines @@
 //       |- - - - - - - - -|   |                        |
 // m+r+3 |  callee-saved r |   v                        v
 //  -----+-----------------+----- <-- stack ptr -------------
 //
 class Frame : public ZoneObject {
  public:
   explicit Frame(int fixed_frame_size_in_slots);
 
   inline int GetTotalFrameSlotCount() const { return frame_slot_count_; }
 
-  inline int GetSavedCalleeRegisterSlotCount() const {
-    return callee_saved_slot_count_;
-  }
   inline int GetSpillSlotCount() const { return spill_slot_count_; }
 
   void SetAllocatedRegisters(BitVector* regs) {
     DCHECK(allocated_registers_ == nullptr);
     allocated_registers_ = regs;
   }
 
   void SetAllocatedDoubleRegisters(BitVector* regs) {
     DCHECK(allocated_double_registers_ == nullptr);
     allocated_double_registers_ = regs;
   }
 
   bool DidAllocateDoubleRegisters() const {
     return !allocated_double_registers_->IsEmpty();
   }
 
-  int AlignSavedCalleeRegisterSlots(int alignment = kDoubleSize) {
-    DCHECK_EQ(0, callee_saved_slot_count_);
+  void AlignSavedCalleeRegisterSlots(int alignment = kDoubleSize) {
     int alignment_slots = alignment / kPointerSize;
     int delta = alignment_slots - (frame_slot_count_ & (alignment_slots - 1));
     if (delta != alignment_slots) {
       frame_slot_count_ += delta;
     }
-    return delta;
+    spill_slot_count_ += delta;

[Mircea Trofin, 2016/04/16 04:25:10]

Note to reviewers: I am not very happy with this. On one hand, aligning here
does change the layout of the
frame, and in a sense, it does this by adding unused spill slots. On the other
hand, I would prefer the 
number of actual spill slots be remembered. I'm concerned with potential access
by the runtime into these
padding slots.

Thoughts?

[Mircea Trofin, 2016/04/16 15:25:43]

FWIW, I see we do the same in AlignFrame. Still, is there any merit to my
concern?

   }
 
   void AllocateSavedCalleeRegisterSlots(int count) {
     frame_slot_count_ += count;
-    callee_saved_slot_count_ += count;
   }
 
   int AllocateSpillSlot(int width) {
-    DCHECK_EQ(0, callee_saved_slot_count_);
     int frame_slot_count_before = frame_slot_count_;
     int slot = AllocateAlignedFrameSlot(width);
     spill_slot_count_ += (frame_slot_count_ - frame_slot_count_before);
     return slot;
   }
 
   int AlignFrame(int alignment = kDoubleSize);
 
   int ReserveSpillSlots(size_t slot_count) {
-    DCHECK_EQ(0, callee_saved_slot_count_);
     DCHECK_EQ(0, spill_slot_count_);
     spill_slot_count_ += static_cast<int>(slot_count);
     frame_slot_count_ += static_cast<int>(slot_count);
     return frame_slot_count_ - 1;
   }
 
   static const int kContextSlot = 2 + StandardFrameConstants::kCPSlotCount;
   static const int kJSFunctionSlot = 3 + StandardFrameConstants::kCPSlotCount;
 
  private:
   int AllocateAlignedFrameSlot(int width) {
     DCHECK(width == 4 || width == 8);
     // Skip one slot if necessary.
     if (width > kPointerSize) {
       DCHECK(width == kPointerSize * 2);
       frame_slot_count_++;
       frame_slot_count_ |= 1;
     }
     return frame_slot_count_++;
   }
 
  private:
   int frame_slot_count_;
-  int callee_saved_slot_count_;
   int spill_slot_count_;
   BitVector* allocated_registers_;
   BitVector* allocated_double_registers_;
 
   DISALLOW_COPY_AND_ASSIGN(Frame);
 };
 
 
 // Represents an offset from either the stack pointer or frame pointer.
 class FrameOffset {
@@ skipping 18 matching lines @@
   int offset_;  // Encodes SP or FP in the low order bit.
 
   static const int kFromSp = 1;
   static const int kFromFp = 0;
 };
 
 // Encapsulates the mutable state maintained during code generation about the
 // current function's frame.
 class FrameAccessState : public ZoneObject {
  public:
-  explicit FrameAccessState(Frame* const frame)
+  explicit FrameAccessState(const Frame* const frame)
       : frame_(frame),
         access_frame_with_fp_(false),
         sp_delta_(0),
         has_frame_(false) {}
 
-  Frame* frame() const { return frame_; }
+  const Frame* frame() const { return frame_; }
   void MarkHasFrame(bool state);
 
   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_; }
 
   // Regardless of how we access slots on the stack - using sp or fp - do we
   // have a frame, at the current stage in code generation.
@@ skipping 11 matching lines @@
   }
   int GetSPToFPOffset() const { return GetSPToFPSlotCount() * kPointerSize; }
 
   // Get the frame offset for a given spill slot. The location depends on the
   // calling convention and the specific frame layout, and may thus be
   // architecture-specific. Negative spill slots indicate arguments on the
   // caller's frame.
   FrameOffset GetFrameOffset(int spill_slot) const;
 
  private:
-  Frame* const frame_;
+  const Frame* const frame_;
   bool access_frame_with_fp_;
   int sp_delta_;
   bool has_frame_;
 };
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_FRAME_H_