Vector ICs: Like megamorphic keyed koads, use a dummy vector for stores

src/ic/arm64/ic-arm64.cc

Index: src/ic/arm64/ic-arm64.cc
diff --git a/src/ic/arm64/ic-arm64.cc b/src/ic/arm64/ic-arm64.cc
index e0bf48b26008f3d3a44faa56ba65f7e35be9318d..e8ce317f0d4c8c58eadaac93d468a761975b4741 100644
--- a/src/ic/arm64/ic-arm64.cc
+++ b/src/ic/arm64/ic-arm64.cc
@@ -397,9 +397,9 @@ static void GenerateKeyedLoadWithNameKey(MacroAssembler* masm, Register key,
   DCHECK(!AreAliased(vector, slot, scratch1, scratch2, scratch3, scratch4));
   Handle<TypeFeedbackVector> dummy_vector = Handle<TypeFeedbackVector>::cast(
       masm->isolate()->factory()->keyed_load_dummy_vector());
-  int int_slot = dummy_vector->GetIndex(FeedbackVectorICSlot(0));
+  int slot_index = dummy_vector->GetIndex(FeedbackVectorICSlot(0));
   __ LoadRoot(vector, Heap::kKeyedLoadDummyVectorRootIndex);
-  __ Mov(slot, Operand(Smi::FromInt(int_slot)));
+  __ Mov(slot, Operand(Smi::FromInt(slot_index)));
 
   Code::Flags flags = Code::RemoveTypeAndHolderFromFlags(
       Code::ComputeHandlerFlags(Code::LOAD_IC));
@@ -663,6 +663,20 @@ void KeyedStoreIC::GenerateMegamorphic(MacroAssembler* masm,
   __ Ldr(x10, FieldMemOperand(key, HeapObject::kMapOffset));
   __ Ldrb(x10, FieldMemOperand(x10, Map::kInstanceTypeOffset));
   __ JumpIfNotUniqueNameInstanceType(x10, &slow);
+
+  if (FLAG_vector_stores) {
+    // The handlers in the stub cache expect a vector and slot. Since we won't
+    // change the IC from any downstream misses, a dummy vector can be used.
+    Register vector = VectorStoreICDescriptor::VectorRegister();
+    Register slot = VectorStoreICDescriptor::SlotRegister();
+    DCHECK(!AreAliased(vector, slot, x3, x4, x5, x6));
+    Handle<TypeFeedbackVector> dummy_vector = Handle<TypeFeedbackVector>::cast(
+        masm->isolate()->factory()->keyed_store_dummy_vector());
+    int slot_index = dummy_vector->GetIndex(FeedbackVectorICSlot(0));
+    __ LoadRoot(vector, Heap::kKeyedStoreDummyVectorRootIndex);
+    __ Mov(slot, Operand(Smi::FromInt(slot_index)));
+  }
+
   Code::Flags flags = Code::RemoveTypeAndHolderFromFlags(
       Code::ComputeHandlerFlags(Code::STORE_IC));
   masm->isolate()->stub_cache()->GenerateProbe(