Provide a tagged allocation top pointer.

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

Index: src/crankshaft/mips/lithium-codegen-mips.cc
diff --git a/src/crankshaft/mips/lithium-codegen-mips.cc b/src/crankshaft/mips/lithium-codegen-mips.cc
index d351db1c56017c73afe427cc9b99c5fa1122cd1d..fc2a5ed316e1f819bec1192766adebf46aeb43d6 100644
--- a/src/crankshaft/mips/lithium-codegen-mips.cc
+++ b/src/crankshaft/mips/lithium-codegen-mips.cc
@@ -5130,10 +5130,8 @@ void LCodeGen::DoDeferredAllocate(LAllocate* instr) {
     ExternalReference allocation_top =
         AllocationUtils::GetAllocationTopReference(isolate(), allocation_flags);
     Register top_address = scratch0();
-    __ Subu(v0, v0, Operand(kHeapObjectTag));
     __ li(top_address, Operand(allocation_top));
     __ sw(v0, MemOperand(top_address));
-    __ Addu(v0, v0, Operand(kHeapObjectTag));
   }
 }