Reland r22247 "ARM64: Use UntagSmi helpers and clean up assertions."

src/arm64/assembler-arm64-inl.h

Index: src/arm64/assembler-arm64-inl.h
diff --git a/src/arm64/assembler-arm64-inl.h b/src/arm64/assembler-arm64-inl.h
index 444f2c4a9455316605d00da9d61a8f2f86ef2fca..a0bcb77e6b5cd7f0eb8bdadfe17119ba01728397 100644
--- a/src/arm64/assembler-arm64-inl.h
+++ b/src/arm64/assembler-arm64-inl.h
@@ -430,12 +430,16 @@ unsigned Operand::shift_amount() const {
 
 
 Operand Operand::UntagSmi(Register smi) {
+  STATIC_ASSERT(kXRegSizeInBits == static_cast<unsigned>(kSmiShift +
+                                                         kSmiValueSize));
   ASSERT(smi.Is64Bits());
   return Operand(smi, ASR, kSmiShift);
 }
 
 
 Operand Operand::UntagSmiAndScale(Register smi, int scale) {
+  STATIC_ASSERT(kXRegSizeInBits == static_cast<unsigned>(kSmiShift +
+                                                         kSmiValueSize));
   ASSERT(smi.Is64Bits());
   ASSERT((scale >= 0) && (scale <= (64 - kSmiValueSize)));
   if (scale > kSmiShift) {