Use the same registers for StoreIC and KeyedStoreIC.

src/arm64/stub-cache-arm64.cc

Index: src/arm64/stub-cache-arm64.cc
diff --git a/src/arm64/stub-cache-arm64.cc b/src/arm64/stub-cache-arm64.cc
index d52493e1536cf3ac8541193365f24c7237141ec8..c3b48a5815e6037c390e5367a7ad254eed9b4d39 100644
--- a/src/arm64/stub-cache-arm64.cc
+++ b/src/arm64/stub-cache-arm64.cc
@@ -1276,10 +1276,11 @@ Register* StoreStubCompiler::registers() {
 
 
 Register* KeyedStoreStubCompiler::registers() {
-  // receiver, name, scratch1, scratch2, scratch3.
+  // receiver, name, scratch1/map, scratch2, scratch3.
   Register receiver = KeyedStoreIC::ReceiverRegister();
   Register name = KeyedStoreIC::NameRegister();
-  static Register registers[] = { receiver, name, x3, x4, x5 };
+  Register map = KeyedStoreIC::MapRegister();
+  static Register registers[] = { receiver, name, map, x4, x5 };
   return registers;
 }
 
@@ -1370,7 +1371,10 @@ Handle<Code> BaseLoadStoreStubCompiler::CompilePolymorphicIC(
   Label* smi_target = IncludesNumberType(types) ? &number_case : &miss;
   __ JumpIfSmi(receiver(), smi_target);
 
+  // Polymorphic keyed stores may use the map register
   Register map_reg = scratch1();
+  ASSERT(kind() != Code::KEYED_STORE_IC ||
+         map_reg.is(KeyedStoreIC::MapRegister()));
   __ Ldr(map_reg, FieldMemOperand(receiver(), HeapObject::kMapOffset));
   int receiver_count = types->length();
   int number_of_handled_maps = 0;