[turbofan] relative_id of splinters and their children.

src/compiler/register-allocator.cc

Index: src/compiler/register-allocator.cc
diff --git a/src/compiler/register-allocator.cc b/src/compiler/register-allocator.cc
index ecf10ae5d64d9a44df3eead45b36bf98d080cf57..482448eb2e6b9dda25c4ab67ee632da0198f426a 100644
--- a/src/compiler/register-allocator.cc
+++ b/src/compiler/register-allocator.cc
@@ -871,6 +871,9 @@ void TopLevelLiveRange::Splinter(LifetimePosition start, LifetimePosition end,
   result->top_level_ = result;
 
   result->SetSplinteredFrom(this);
+  // Ensure the result's relative ID is unique within the IDs used for this
+  // virtual register's children and splinters.
+  result->relative_id_ = GetNextChildId();
 }