Optimize testing for an index's existence in packed Arrays

src/arm/full-codegen-arm.cc

Index: src/arm/full-codegen-arm.cc
diff --git a/src/arm/full-codegen-arm.cc b/src/arm/full-codegen-arm.cc
index fbf3fec6c885ac0f23605ba0b02d93115a996593..57a1e39cbc55b68ec2333dc4265b409bc4fe2205 100644
--- a/src/arm/full-codegen-arm.cc
+++ b/src/arm/full-codegen-arm.cc
@@ -4378,6 +4378,40 @@ 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 = r0;
+  Register map = r1;
+  Register elements_kind = r2;
+
+  __ JumpIfSmi(object, if_false);
+  __ ldr(map, FieldMemOperand(object, HeapObject::kMapOffset));
+  __ ldrb(elements_kind, FieldMemOperand(map, Map::kBitField2Offset));
+  __ mov(elements_kind,
+         Operand(elements_kind, LSR, 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) {