ARM64: Optimize generated code for gaps

src/arm64/lithium-gap-resolver-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_LITHIUM_GAP_RESOLVER_ARM64_H_
 #define V8_ARM64_LITHIUM_GAP_RESOLVER_ARM64_H_
 
 #include "src/v8.h"
 
 #include "src/lithium.h"
+#include "src/arm64/delayed-masm-arm64.h"
 
 namespace v8 {
 namespace internal {
 
 class LCodeGen;
 class LGapResolver;
 
+class DelayedGapMasm : public DelayedMasm {
+ public:
+  DelayedGapMasm(LCodeGen* owner, MacroAssembler* masm)
+    : DelayedMasm(owner, masm, root) {
+    // We use the root register as an extra scratch register.
+    // The root register has two advantages:
+    //  - It is not in crankshaft allocatable registers list, so it can't
+    //    interfere with the allocatable registers.
+    //  - We don't need to push it on the stack, as we can reload it with its
+    //    value once we have finish.
+  }
+  void EndDelayedUse();
+};
+
+
 class LGapResolver BASE_EMBEDDED {
  public:
   explicit LGapResolver(LCodeGen* owner);
 
   // Resolve a set of parallel moves, emitting assembler instructions.
   void Resolve(LParallelMove* parallel_move);
 
  private:
   // Build the initial list of moves.
   void BuildInitialMoveList(LParallelMove* parallel_move);
 
   // Perform the move at the moves_ index in question (possibly requiring
   // other moves to satisfy dependencies).
   void PerformMove(int index);
 
   // If a cycle is found in the series of moves, save the blocking value to
   // a scratch register.  The cycle must be found by hitting the root of the
   // depth-first search.
   void BreakCycle(int index);
 
   // After a cycle has been resolved, restore the value from the scratch
   // register to its proper destination.
   void RestoreValue();
 
   // Emit a move and remove it from the move graph.
   void EmitMove(int index);
 
   // Emit a move from one stack slot to another.
-  void EmitStackSlotMove(int index);
+  void EmitStackSlotMove(int index) {
+    masm_.StackSlotMove(moves_[index].source(), moves_[index].destination());
+  }
 
   // Verify the move list before performing moves.
   void Verify();
 
+  // Registers used to solve cycles.
+  const Register& SavedValueRegister() {
+    ASSERT(!masm_.ScratchRegister().IsAllocatable());
+    return masm_.ScratchRegister();
+  }
+  // The scratch register is used to break cycles and to store constant.
+  // These two methods switch from one mode to the other.
+  void AcquireSavedValueRegister() { masm_.AcquireScratchRegister(); }
+  void ReleaseSavedValueRegister() { masm_.ReleaseScratchRegister(); }
+  const FPRegister& SavedFPValueRegister() {
+    // We use the Crankshaft floating-point scratch register to break a cycle
+    // involving double values as the MacroAssembler will not need it for the
+    // operations performed by the gap resolver.
+    ASSERT(!crankshaft_fp_scratch.IsAllocatable());
+    return crankshaft_fp_scratch;
+  }
+
   LCodeGen* cgen_;
+  DelayedGapMasm masm_;
 
   // List of moves not yet resolved.
   ZoneList<LMoveOperands> moves_;
 
   int root_index_;
   bool in_cycle_;
   LOperand* saved_destination_;
-
-  // We use the root register as a scratch in a few places. When that happens,
-  // this flag is set to indicate that it needs to be restored.
-  bool need_to_restore_root_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM64_LITHIUM_GAP_RESOLVER_ARM64_H_