ARM64: Support arbitrary offset in load/store pair.

src/arm64/assembler-arm64.cc

Index: src/arm64/assembler-arm64.cc
diff --git a/src/arm64/assembler-arm64.cc b/src/arm64/assembler-arm64.cc
index dc2d587f177d1ba3f7653b09ab2aac0448ed8d25..7f86e14a777c77109bb8d1441581f5c094b73d57 100644
--- a/src/arm64/assembler-arm64.cc
+++ b/src/arm64/assembler-arm64.cc
@@ -2503,6 +2503,12 @@ bool Assembler::IsImmLSScaled(ptrdiff_t offset, LSDataSize size) {
 }
 
 
+bool Assembler::IsImmLSPair(ptrdiff_t offset, LSDataSize size) {
+  bool offset_is_size_multiple = (((offset >> size) << size) == offset);
+  return offset_is_size_multiple && is_int7(offset >> size);
+}
+
+
 // Test if a given value can be encoded in the immediate field of a logical
 // instruction.
 // If it can be encoded, the function returns true, and values pointed to by n,