Hydrogen array constructor cleanup and improvements

src/x64/code-stubs-x64.cc

Index: src/x64/code-stubs-x64.cc
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index ab3064fc26bfb5552a43ffcc7b91c0161b434bbc..c8bee9d90ecd546f3a9825a6a967c4868e7fe5a1 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -3739,12 +3739,7 @@ static void GenerateRecordCallTarget(MacroAssembler* masm) {
   // Special handling of the Array() function, which caches not only the
   // monomorphic Array function but the initial ElementsKind with special
   // sentinels
-  Handle<Object> terminal_kind_sentinel =
-      TypeFeedbackCells::MonomorphicArraySentinel(isolate,
-                                                  LAST_FAST_ELEMENTS_KIND);
   __ JumpIfNotSmi(rcx, &miss);
-  __ Cmp(rcx, terminal_kind_sentinel);
-  __ j(above, &miss);
   // Make sure the function is the Array() function
   __ LoadArrayFunction(rcx);
   __ cmpq(rdi, rcx);
@@ -6801,6 +6796,10 @@ static void CreateArrayDispatchOneArgument(MacroAssembler* masm) {
   __ Cmp(rbx, undefined_sentinel);
   __ j(equal, &normal_sequence);
 
+  // The type cell may have gone megamorphic, don't overwrite if so
+  __ movq(rcx, FieldOperand(rbx, kPointerSize));
+  __ JumpIfNotSmi(rcx, &normal_sequence);
+
   // Save the resulting elements kind in type info
   __ Integer32ToSmi(rdx, rdx);
   __ movq(FieldOperand(rbx, kPointerSize), rdx);