Generalize ExtractFixedArray's branch for Smis or Objects.

This CL extracts the branch into a new function. Previously, the branch
is only used to copy a FixedArray to a new FixedArray. The new function
generalizes this to allow copying from a FixedDoubleArray to a
FixedArray also. This function will be useful in a follow-up CL to copy
a FixedDoubleArray with holes into a FixedArray where holes are replaced
by undefined.

Bug: chromium:881273, v8:7980

Change-Id: I8a0e5f933fc152a12d67810f4cbcfdce094d44af
Reviewed-on: https://chromium-review.googlesource.com/1230913
Commit-Queue: Hai Dang <dhai@google.com>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56101}

src/code-stub-assembler.h

@@ -1554,8 +1554,8 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
   typedef base::Flags<ExtractFixedArrayFlag> ExtractFixedArrayFlags;
 
   // Copy a portion of an existing FixedArray or FixedDoubleArray into a new
-  // FixedArray, including special appropriate handling for empty arrays and COW
-  // arrays.
+  // array, including special appropriate handling for empty arrays and COW
+  // arrays. The result array will be of the same type as the original array.
   //
   // * |source| is either a FixedArray or FixedDoubleArray from which to copy
   // elements.
@@ -1591,6 +1591,33 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
                              SMI_PARAMETERS);
   }
 
+  // Copy a portion of an existing FixedArray or FixedDoubleArray into a new
+  // FixedArray, including special appropriate handling for COW arrays.
+  // * |source| is either a FixedArray or FixedDoubleArray from which to copy
+  // elements. |source| is assumed to be non-empty.
+  // * |first| is the starting element index to copy from.
+  // * |count| is the number of elements to copy out of the source array
+  // starting from and including the element indexed by |start|.
+  // * |capacity| determines the size of the allocated result array, with
+  // |capacity| >= |count|.
+  // * |source_map| is the map of the |source|.
+  // * |from_kind| is the elements kind that is consistent with |source| being
+  // a FixedArray or FixedDoubleArray. This function only cares about double vs.
+  // non-double, so as to distinguish FixedDoubleArray vs. FixedArray. It does
+  // not care about holeyness. For example, when |source| is a FixedArray,
+  // PACKED/HOLEY_ELEMENTS can be used, but not PACKED_DOUBLE_ELEMENTS.
+  // * The function uses |allocation_flags| and |extract_flags| to decide how to
+  // allocate the result FixedArray.
+  // * |parameter_mode| determines the parameter mode of |first|, |count| and
+  // |capacity|.
+  TNode<FixedArray> ExtractToFixedArray(
+      Node* source, Node* first, Node* count, Node* capacity, Node* source_map,
+      ElementsKind from_kind = PACKED_ELEMENTS,
+      AllocationFlags allocation_flags = AllocationFlag::kNone,
+      ExtractFixedArrayFlags extract_flags =
+          ExtractFixedArrayFlag::kAllFixedArrays,
+      ParameterMode parameter_mode = INTPTR_PARAMETERS);
+
   // Copy the entire contents of a FixedArray or FixedDoubleArray to a new
   // array, including special appropriate handling for empty arrays and COW
   // arrays.