ARM64: Optimize generated code for gaps

src/arm64/assembler-arm64.h

Index: src/arm64/assembler-arm64.h
diff --git a/src/arm64/assembler-arm64.h b/src/arm64/assembler-arm64.h
index c0ad4d053b184141221b70363592a6ee104dde01..653c4290790696aef4b56d01d9d6aa21049ae98d 100644
--- a/src/arm64/assembler-arm64.h
+++ b/src/arm64/assembler-arm64.h
@@ -729,6 +729,16 @@ class MemOperand {
   // handle indexed modes.
   inline Operand OffsetAsOperand() const;
 
+  enum PairResult {
+    kNotPair,   // Can't use a pair instruction.
+    kPairAB,    // Can use a pair instruction (operandA has lower address).
+    kPairBA     // Can use a pair instruction (operandB has lower address).
+  };
+  // Check if two MemOperand are consistent for stp/ldp use.
+  static PairResult AreConsistentForPair(const MemOperand& operandA,
+                                         const MemOperand& operandB,
+                                         int access_size_log2 = kXRegSizeLog2);
+
  private:
   Register base_;
   Register regoffset_;