[runtime/heap] Introduce CopyFixedArrayUpTo to match CopyFixedArrayAndGrow, copying to a smaller ar…

src/heap/heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/ast/scopeinfo.h"
 #include "src/base/bits.h"
@@ skipping 3763 matching lines @@
 AllocationResult Heap::CopyFixedArrayAndGrow(FixedArray* src, int grow_by,
                                              PretenureFlag pretenure) {
   int old_len = src->length();
   int new_len = old_len + grow_by;
   DCHECK(new_len >= old_len);
   HeapObject* obj = nullptr;
   {
     AllocationResult allocation = AllocateRawFixedArray(new_len, pretenure);
     if (!allocation.To(&obj)) return allocation;
   }
+
   obj->set_map_no_write_barrier(fixed_array_map());
   FixedArray* result = FixedArray::cast(obj);
   result->set_length(new_len);
 
   // Copy the content.
   DisallowHeapAllocation no_gc;
-  WriteBarrierMode mode = result->GetWriteBarrierMode(no_gc);
+  WriteBarrierMode mode = obj->GetWriteBarrierMode(no_gc);
   for (int i = 0; i < old_len; i++) result->set(i, src->get(i), mode);
   MemsetPointer(result->data_start() + old_len, undefined_value(), grow_by);
   return result;
 }
 
+AllocationResult Heap::CopyFixedArrayUpTo(FixedArray* src, int new_len,
+                                          PretenureFlag pretenure) {
+  if (new_len == 0) return empty_fixed_array();
+
+  DCHECK_LE(new_len, src->length());
+
+  HeapObject* obj = nullptr;
+  {
+    AllocationResult allocation = AllocateRawFixedArray(new_len, pretenure);
+    if (!allocation.To(&obj)) return allocation;
+  }
+  obj->set_map_no_write_barrier(fixed_array_map());
+
+  FixedArray* result = FixedArray::cast(obj);
+  result->set_length(new_len);
+
+  // Copy the content.
+  DisallowHeapAllocation no_gc;
+  WriteBarrierMode mode = result->GetWriteBarrierMode(no_gc);
+  for (int i = 0; i < new_len; i++) result->set(i, src->get(i), mode);
+  return result;
+}
 
 AllocationResult Heap::CopyFixedArrayWithMap(FixedArray* src, Map* map) {
   int len = src->length();
   HeapObject* obj = nullptr;
   {
     AllocationResult allocation = AllocateRawFixedArray(len, NOT_TENURED);
     if (!allocation.To(&obj)) return allocation;
   }
+  obj->set_map_no_write_barrier(map);
   if (InNewSpace(obj)) {
-    obj->set_map_no_write_barrier(map);
     CopyBlock(obj->address() + kPointerSize, src->address() + kPointerSize,
               FixedArray::SizeFor(len) - kPointerSize);
     return obj;
   }
-  obj->set_map_no_write_barrier(map);
   FixedArray* result = FixedArray::cast(obj);
   result->set_length(len);
 
   // Copy the content.
   DisallowHeapAllocation no_gc;
   WriteBarrierMode mode = result->GetWriteBarrierMode(no_gc);
   for (int i = 0; i < len; i++) result->set(i, src->get(i), mode);
   return result;
 }
 
@@ skipping 2393 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8