Make BitField3 a raw uint32 field, and move to the start of the map.

src/arm64/macro-assembler-arm64.cc

Index: src/arm64/macro-assembler-arm64.cc
diff --git a/src/arm64/macro-assembler-arm64.cc b/src/arm64/macro-assembler-arm64.cc
index c5ce99be9924c624b493a166fe5f0da71561700d..e632ae6bca8a0b3fd56464677d451ee304d81bda 100644
--- a/src/arm64/macro-assembler-arm64.cc
+++ b/src/arm64/macro-assembler-arm64.cc
@@ -1329,15 +1329,14 @@ void MacroAssembler::NumberOfOwnDescriptors(Register dst, Register map) {
 
 void MacroAssembler::EnumLengthUntagged(Register dst, Register map) {
   STATIC_ASSERT(Map::EnumLengthBits::kShift == 0);
-  Ldrsw(dst, UntagSmiFieldMemOperand(map, Map::kBitField3Offset));
+  Ldrsw(dst, FieldMemOperand(map, Map::kBitField3Offset));
   And(dst, dst, Map::EnumLengthBits::kMask);
 }
 
 
 void MacroAssembler::EnumLengthSmi(Register dst, Register map) {
-  STATIC_ASSERT(Map::EnumLengthBits::kShift == 0);
-  Ldr(dst, FieldMemOperand(map, Map::kBitField3Offset));
-  And(dst, dst, Smi::FromInt(Map::EnumLengthBits::kMask));
+  EnumLengthUntagged(dst, map);
+  SmiTag(dst, dst);
 }
 
 
@@ -4519,7 +4518,7 @@ void MacroAssembler::CheckMapDeprecated(Handle<Map> map,
                                         Label* if_deprecated) {
   if (map->CanBeDeprecated()) {
     Mov(scratch, Operand(map));
-    Ldrsw(scratch, UntagSmiFieldMemOperand(scratch, Map::kBitField3Offset));
+    Ldrsw(scratch, FieldMemOperand(scratch, Map::kBitField3Offset));
     TestAndBranchIfAnySet(scratch, Map::Deprecated::kMask, if_deprecated);
   }
 }