ARM64: Optimize generated code for gaps

src/arm64/delayed-masm-arm64.h

+// Copyright 2013 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_ARM64_DELAYED_MASM_ARM64_H_
+#define V8_ARM64_DELAYED_MASM_ARM64_H_
+
+#include "src/lithium.h"
+
+namespace v8 {
+namespace internal {
+
+class LCodeGen;
+
+// This class delays the generation of some instructions. This way, we have a
+// chance to merge two instructions in one (with load/store pair).
+// Each instruction must either:
+//  - merge with the pending instruction and generate just one instruction.
+//  - emit the pending instruction and then generate the instruction (or set the
+//    pending instruction).
+class DelayedMasm BASE_EMBEDDED {
+ public:
+  DelayedMasm(LCodeGen* owner,
+              MacroAssembler* masm,
+              const Register& scratch_register)
+    : cgen_(owner), masm_(masm), scratch_register_(scratch_register),
+      scratch_register_used_(false), pending_(kNone), saved_value_(0) {
+#ifdef DEBUG
+    pending_register_ = no_reg;
+    pending_value_ = 0;
+    pending_pc_ = 0;
+    scratch_register_acquired_ = false;
+#endif
+  }
+  ~DelayedMasm() {
+    ASSERT(!scratch_register_acquired_);
+    ASSERT(!scratch_register_used_);
+    ASSERT(!pending());
+  }
+  inline void EndDelayedUse();
+
+  const Register& ScratchRegister() {
+    scratch_register_used_ = true;
+    return scratch_register_;
+  }
+  bool IsScratchRegister(const CPURegister& reg) {
+    return reg.Is(scratch_register_);
+  }
+  bool scratch_register_used() const { return scratch_register_used_; }
+  void reset_scratch_register_used() { scratch_register_used_ = false; }
+  // Acquire/Release scratch register for use outside this class.
+  void AcquireScratchRegister() {
+#ifdef DEBUG
+    ASSERT(!scratch_register_acquired_);
+    scratch_register_acquired_ = true;

[ulan, 2014/06/10 08:54:40]

Shouldn't we reset the saved value here since no longer control the scratch
register? 

[vincent.belliard, 2014/06/10 09:00:12]

This function is only used in debug to ensure that we don't use the scratch
register for a constant while the register is acquired.
If the scratch register is really used after acquired, the saved value will be
reset (or set to an other value).

[vincent.belliard, 2014/06/12 12:57:57]

Done.

+#endif
+  }
+  void ReleaseScratchRegister() {
+#ifdef DEBUG
+    ASSERT(scratch_register_acquired_);
+    scratch_register_acquired_ = false;
+#endif
+  }
+  bool pending() { return pending_ != kNone; }
+
+  // Extra layer over the macro-assembler instructions (which emits the
+  // potential pending instruction).
+  inline void Mov(const Register& rd,
+                  const Operand& operand,
+                  DiscardMoveMode discard_mode = kDontDiscardForSameWReg);
+  inline void Fmov(FPRegister fd, FPRegister fn);
+  inline void Fmov(FPRegister fd, double imm);
+  inline void LoadObject(Register result, Handle<Object> object);
+  // Instructions which try to merge which the pending instructions.
+  void StackSlotMove(LOperand* src, LOperand* dst);
+  // StoreConstant can only be used if the scratch register is not acquired.
+  void StoreConstant(uint64_t value, const MemOperand& operand);
+  void Load(const CPURegister& rd, const MemOperand& operand);
+  void Store(const CPURegister& rd, const MemOperand& operand);
+  // Emit the potential pending instruction.
+  void EmitPending();
+  // Reset the pending state.
+  void ResetPending() {
+    pending_ = kNone;
+#ifdef DEBUG
+    pending_register_ = no_reg;
+    MemOperand tmp;
+    pending_address_src_ = tmp;
+    pending_address_dst_ = tmp;
+    pending_value_ = 0;
+    pending_pc_ = 0;
+#endif
+  }
+  void InitializeRootRegister() {
+    masm_->InitializeRootRegister();
+  }
+
+ private:
+  // Set the saved value and load the ScratchRegister with it.
+  void SetSavedValue(uint64_t saved_value) {
+    ASSERT(saved_value != 0);
+    if (saved_value_ != saved_value) {
+      masm_->Mov(ScratchRegister(), saved_value);
+      saved_value_ = saved_value;
+    }
+  }
+  // Reset the saved value (i.e. the value of ScratchRegister is no longer
+  // known).
+  void ResetSavedValue() {
+    saved_value_ = 0;
+  }
+
+  LCodeGen* cgen_;
+  MacroAssembler* masm_;
+
+  // Register used to store a constant.
+  Register scratch_register_;
+  bool scratch_register_used_;
+
+  // Sometimes we store or load two values in two contiguous stack slots.
+  // In this case, we try to use the ldp/stp instructions to reduce code size.
+  // To be able to do that, instead of generating directly the instructions,
+  // we register with the following fields that an instruction needs to be
+  // generated. Then with the next instruction, if the instruction is
+  // consistent with the pending one for stp/ldp we generate ldp/stp. Else,
+  // if they are not consistent, we generate the pending instruction and we
+  // register the new instruction (which becomes pending).
+
+  // Enumeration of instructions which can be pending.
+  enum Pending {
+    kNone,
+    kStoreConstant,
+    kLoad, kStore,
+    kStackSlotMove
+  };
+  // The pending instruction.
+  Pending pending_;
+  // For kLoad, kStore: register which must be loaded/stored.
+  CPURegister pending_register_;
+  // For kLoad, kStackSlotMove: address of the load.
+  MemOperand pending_address_src_;
+  // For kStoreConstant, kStore, kStackSlotMove: address of the store.
+  MemOperand pending_address_dst_;
+  // For kStoreConstant: value to be stored.
+  uint64_t pending_value_;
+  // Value held into the ScratchRegister if the saved_value_ is not 0.
+  // For 0, we use xzr.
+  uint64_t saved_value_;
+#ifdef DEBUG
+  // Address where the pending instruction must be generated. It's only used to
+  // check that nothing else has been generated since we set the pending
+  // instruction.
+  int pending_pc_;
+  // If true, the scratch register has been acquired outside this class. The
+  // scratch register can no longer be used for constants.
+  bool scratch_register_acquired_;
+#endif
+};
+
+} }  // namespace v8::internal
+
+#endif  // V8_ARM64_DELAYED_MASM_ARM64_H_