[turbofan] Frame elision for code stubs

src/compiler/code-generator.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_CODE_GENERATOR_H_
 #define V8_COMPILER_CODE_GENERATOR_H_
 
 #include "src/compiler/gap-resolver.h"
 #include "src/compiler/instruction.h"
 #include "src/deoptimizer.h"
@@ skipping 39 matching lines @@
                          InstructionSequence* code, CompilationInfo* info);
 
   // Generate native code.
   Handle<Code> GenerateCode();
 
   InstructionSequence* code() const { return code_; }
   FrameAccessState* frame_access_state() const { return frame_access_state_; }
   Frame* frame() const { return frame_access_state_->frame(); }
   Isolate* isolate() const { return info_->isolate(); }
   Linkage* linkage() const { return linkage_; }
-
+  bool deconstruct_frame_when_leaving() const {
+    return deconstruct_frame_when_leaving_;
+  }
+  void set_deconstruct_frame_when_leaving(bool deconstruct) {
+    deconstruct_frame_when_leaving_ = deconstruct;
+  }
+  bool deconstruct_frame_between_blocks() const {
+    return deconstruct_frame_between_blocks_;
+  }
+  void set_deconstruct_frame_between_blocks(bool deconstruct) {
+    deconstruct_frame_between_blocks_ = deconstruct;
+  }
   Label* GetLabel(RpoNumber rpo) { return &labels_[rpo.ToSize()]; }
 
  private:
   MacroAssembler* masm() { return &masm_; }
   GapResolver* resolver() { return &resolver_; }
   SafepointTableBuilder* safepoints() { return &safepoints_; }
   Zone* zone() const { return code()->zone(); }
   CompilationInfo* info() const { return info_; }
 
   // Checks if {block} will appear directly after {current_block_} when
@@ skipping 28 matching lines @@
   void AssembleArchBoolean(Instruction* instr, FlagsCondition condition);
   void AssembleArchLookupSwitch(Instruction* instr);
   void AssembleArchTableSwitch(Instruction* instr);
 
   void AssembleDeoptimizerCall(int deoptimization_id,
                                Deoptimizer::BailoutType bailout_type);
 
   // Generates an architecture-specific, descriptor-specific prologue
   // to set up a stack frame.
   void AssemblePrologue();
+
+  // Setup the type of frame access, and the occupied slots, based on the
+  // needs of the block.
+  void SetupFrameAccessForBlock(const InstructionBlock* block);
+
+  void SetupStackPointer();
+
   // Generates an architecture-specific, descriptor-specific return sequence
   // to tear down a stack frame.
   void AssembleReturn();
 
   // Generates code to deconstruct a the caller's frame, including arguments.
   void AssembleDeconstructActivationRecord(int stack_param_delta);
 
+  void AssembleDeconstructFrameWhenLeaving() {
+    if (deconstruct_frame_when_leaving()) {
+      AssembleDeconstructFrame();
+      set_deconstruct_frame_between_blocks(false);
+      set_deconstruct_frame_when_leaving(false);
+    }
+  }
+
+  void AssembleDeconstructFrameBetweenBlocks() {
+    if (deconstruct_frame_between_blocks()) {
+      AssembleDeconstructFrame();
+      set_deconstruct_frame_between_blocks(false);
+      set_deconstruct_frame_when_leaving(false);
+    }
+  }
+
+  void AssembleDeconstructFrame();
+
   // Generates code to manipulate the stack in preparation for a tail call.
   void AssemblePrepareTailCall(int stack_param_delta);
 
   // Generates code to pop current frame if it is an arguments adaptor frame.
   void AssemblePopArgumentsAdaptorFrame(Register args_reg, Register scratch1,
                                         Register scratch2, Register scratch3);
 
   // ===========================================================================
   // ============== Architecture-specific gap resolver methods. ================
   // ===========================================================================
@@ skipping 94 matching lines @@
   ZoneVector<HandlerInfo> handlers_;
   ZoneDeque<DeoptimizationExit*> deoptimization_exits_;
   ZoneDeque<DeoptimizationState*> deoptimization_states_;
   ZoneDeque<Handle<Object>> deoptimization_literals_;
   size_t inlined_function_count_;
   TranslationBuffer translations_;
   int last_lazy_deopt_pc_;
   JumpTable* jump_tables_;
   OutOfLineCode* ools_;
   int osr_pc_offset_;
+  bool deconstruct_frame_when_leaving_;

[danno, 2016/03/16 18:18:11]

I don't think you want this variable here, I think it's much better encapsulated
in the frame_access_state. I would much prefer a boolean on the
frame_access_state called currently_has_frame_. If starts out as false, and you
can query it. As you run through the blocks, you set it depending on
must_construct/deconstruct frame.

There would also be a method called SetCurrentlyHasFrame, it would look
something like this (maybe better in two methods, ConstructFrame and
DeconstructFrame with appropriate asserts.

SetCurrentlyHasFrame(bool has_frame) {
  has_frame_ = has_frame;
  if (has_frame) {
    SetFrameAccessToDefault();
  } else {
    SetFrameAccessToSP();
  }
}

GetSPToFPSlotCount would also be simpler, and for the most part remains
unchanged.

GetSPToFPSlotCount() {
 int used_slots = has_frame_ ? frame_->GetSPToFPSlotCount() :
(kElidedFrameSlotCount - StandardFrameConstants::kFixedSlotCountAboveFp);
 return used_slots + sp_delta()
}

Then, at the end of the method, you just query frame_access_state()->has_frame()
to know if you need to deconstruct the frame.

[Mircea Trofin, 2016/03/16 20:20:46]

I agree, this was from my 3 month old prototype.

+  bool deconstruct_frame_between_blocks_;

[danno, 2016/03/16 18:18:11]

I don't think this boolean belongs here at all. See my comment in the .cc file
about pushing this into the block->must_deconstruct_frame() decision, and that
logic should be in the frame elision pass or in instruction selection or
wherever, but not here.

 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_CODE_GENERATOR_H