Optimize testing for an index's existence in packed Arrays

src/ia32/full-codegen-ia32.cc

Index: src/ia32/full-codegen-ia32.cc
diff --git a/src/ia32/full-codegen-ia32.cc b/src/ia32/full-codegen-ia32.cc
index 672b46bb2568859538118bc11e82d28c74f877d1..68ef3291b6f868d02fbe892ad88790abc40f44b0 100644
--- a/src/ia32/full-codegen-ia32.cc
+++ b/src/ia32/full-codegen-ia32.cc
@@ -4321,6 +4321,35 @@ 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);
+
+  __ JumpIfSmi(eax, if_false);
+  __ mov(eax, FieldOperand(eax, HeapObject::kMapOffset));
+  __ movzx_b(eax, FieldOperand(eax, Map::kBitField2Offset));
+  __ shr(eax, Map::ElementsKindBits::kShift);
+  __ cmp(eax, Immediate(FAST_SMI_ELEMENTS));
+  __ j(equal, if_true);
+  __ cmp(eax, Immediate(FAST_ELEMENTS));
+  __ j(equal, if_true);
+  __ cmp(eax, Immediate(FAST_DOUBLE_ELEMENTS));
+  PrepareForBailoutBeforeSplit(expr, true, if_true, if_false);
+  Split(equal, 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) {