Optimize testing for an index's existence in packed Arrays

src/arm64/full-codegen-arm64.cc

Index: src/arm64/full-codegen-arm64.cc
diff --git a/src/arm64/full-codegen-arm64.cc b/src/arm64/full-codegen-arm64.cc
index 710956ffd304b4f67297294a8448187246c8d805..66deb1e08516790a89a73b138bde83857aeb43ce 100644
--- a/src/arm64/full-codegen-arm64.cc
+++ b/src/arm64/full-codegen-arm64.cc
@@ -4067,6 +4067,39 @@ void FullCodeGenerator::EmitDebugIsActive(CallRuntime* expr) {
 }
 
 
+void FullCodeGenerator::EmitHasFastPackedElements(CallRuntime* expr) {
+  ZoneList<Expression*>* args = expr->arguments();
+  DCHECK(args->length() == 1);
+
+  VisitForAccumulatorValue(args->at(0));
+
+  Label materialize_true, materialize_false;
+  Label* if_true = NULL;
+  Label* if_false = NULL;
+  Label* fall_through = NULL;
+  context()->PrepareTest(&materialize_true, &materialize_false, &if_true,
+                         &if_false, &fall_through);
+
+  Register object = x0;
+  Register map = x10;
+  Register elements_kind = x11;
+
+  __ JumpIfSmi(object, if_false);
+  __ Ldr(map, FieldMemOperand(object, HeapObject::kMapOffset));
+  __ Ldrb(elements_kind, FieldMemOperand(map, Map::kBitField2Offset));
+  __ Lsr(elements_kind, elements_kind, Map::ElementsKindBits::kShift);
+  __ Cmp(elements_kind, Operand(FAST_SMI_ELEMENTS));
+  __ B(eq, if_true);
+  __ Cmp(elements_kind, Operand(FAST_ELEMENTS));
+  __ B(eq, if_true);
+  __ Cmp(elements_kind, Operand(FAST_DOUBLE_ELEMENTS));
+  PrepareForBailoutBeforeSplit(expr, true, if_true, if_false);
+  Split(eq, if_true, if_false, fall_through);
+
+  context()->Plug(if_true, if_false);
+}
+
+
 void FullCodeGenerator::VisitCallRuntime(CallRuntime* expr) {
   if (expr->function() != NULL &&
       expr->function()->intrinsic_type == Runtime::INLINE) {