Revert of Provide a tagged allocation top pointer.

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 0c3f231a3f17e382cbe33350150ec777922f2416..0490c388d9bbbb8c79a01639edd58a75abb338a8 100644
--- a/src/arm64/macro-assembler-arm64.cc
+++ b/src/arm64/macro-assembler-arm64.cc
@@ -3097,6 +3097,9 @@
     // The top pointer is not updated for allocation folding dominators.
     Str(result_end, MemOperand(top_address));
   }
+
+  // Tag the object.
+  ObjectTag(result, result);
 }
 
 
@@ -3166,7 +3169,7 @@
 
   if (emit_debug_code()) {
     Tst(result_end, kObjectAlignmentMask);
-    Check(ne, kUnalignedAllocationInNewSpace);
+    Check(eq, kUnalignedAllocationInNewSpace);
   }
 
   Ccmp(result_end, alloc_limit, NoFlag, cc);
@@ -3176,6 +3179,9 @@
     // The top pointer is not updated for allocation folding dominators.
     Str(result_end, MemOperand(top_address));
   }
+
+  // Tag the object.
+  ObjectTag(result, result);
 }
 
 void MacroAssembler::FastAllocate(int object_size, Register result,
@@ -3208,6 +3214,8 @@
   // Calculate new top and write it back.
   Adds(result_end, result, object_size);
   Str(result_end, MemOperand(top_address));
+
+  ObjectTag(result, result);
 }
 
 void MacroAssembler::FastAllocate(Register object_size, Register result,
@@ -3241,8 +3249,10 @@
 
   if (emit_debug_code()) {
     Tst(result_end, kObjectAlignmentMask);
-    Check(ne, kUnalignedAllocationInNewSpace);
-  }
+    Check(eq, kUnalignedAllocationInNewSpace);
+  }
+
+  ObjectTag(result, result);
 }
 
 void MacroAssembler::AllocateTwoByteString(Register result,