Provide a tagged allocation top pointer.

src/crankshaft/arm/lithium-codegen-arm.cc

Index: src/crankshaft/arm/lithium-codegen-arm.cc
diff --git a/src/crankshaft/arm/lithium-codegen-arm.cc b/src/crankshaft/arm/lithium-codegen-arm.cc
index 8eda5922f428547bfe55c7e7c5f11c07447bf94e..af35da341eb6ab63e51704ac35f1bf91c9cd96e1 100644
--- a/src/crankshaft/arm/lithium-codegen-arm.cc
+++ b/src/crankshaft/arm/lithium-codegen-arm.cc
@@ -5162,10 +5162,8 @@ void LCodeGen::DoDeferredAllocate(LAllocate* instr) {
     ExternalReference allocation_top =
         AllocationUtils::GetAllocationTopReference(isolate(), allocation_flags);
     Register top_address = scratch0();
-    __ sub(r0, r0, Operand(kHeapObjectTag));
     __ mov(top_address, Operand(allocation_top));
     __ str(r0, MemOperand(top_address));
-    __ add(r0, r0, Operand(kHeapObjectTag));
   }
 }