[regalloc] Also use bundles for splinters

With this change, splinters inherit the bundle from
their parent and hence get the same registers allocated
(if possible) that are used by the parent. This might
improve performance and should reduce code size.

Change-Id: I0f3b5211cf47976a16b37204a1ce34d92725bc33
Reviewed-on: https://chromium-review.googlesource.com/c/1403126
Commit-Queue: Stephan Herhut <herhut@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58840}

src/compiler/backend/register-allocator.h

@@ -681,6 +681,7 @@ class V8_EXPORT_PRIVATE TopLevelLiveRange final : public LiveRange {
     splinter->relative_id_ = GetNextChildId();
     splinter->set_spill_type(spill_type());
     splinter->SetSplinteredFrom(this);
+    if (bundle_ != nullptr) splinter->set_bundle(bundle_);
   }
 
   void MarkHasPreassignedSlot() { has_preassigned_slot_ = true; }