Refactor and improve inlined double-aligned allocations

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 f950368404804ada7d78da991bc0b6ca2464a288..9e948a92b724b0ceaa8516cf2eb5305df430e65f 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -333,7 +333,11 @@ static void GenerateFastCloneShallowArrayCommon(
 
   // Allocate both the JS array and the elements array in one big
   // allocation. This avoids multiple limit checks.
-  __ AllocateInNewSpace(size, rax, rbx, rdx, fail, TAG_OBJECT);
+  AllocationFlags flags = TAG_OBJECT;
+  if (mode == FastCloneShallowArrayStub::CLONE_DOUBLE_ELEMENTS) {
+    flags = static_cast<AllocationFlags>(DOUBLE_ALIGNMENT | flags);
+  }
+  __ AllocateInNewSpace(size, rax, rbx, rdx, fail, flags);
 
   // Copy the JS array part.
   for (int i = 0; i < JSArray::kSize; i += kPointerSize) {