[Turbofan] Re-enable single splinter.

src/compiler/live-range-separator.cc

Index: src/compiler/live-range-separator.cc
diff --git a/src/compiler/live-range-separator.cc b/src/compiler/live-range-separator.cc
index 44e9dba7b58b13e9e80bc82f1a9cb6cb79b47f6a..d81885f68f6fd07b4f207db24cb4cc26e3f771bf 100644
--- a/src/compiler/live-range-separator.cc
+++ b/src/compiler/live-range-separator.cc
@@ -44,12 +44,14 @@ void CreateSplinter(TopLevelLiveRange *range, RegisterAllocationData *data,
     if (range->MayRequireSpillRange()) {
       data->CreateSpillRangeForLiveRange(range);
     }
-    TopLevelLiveRange *result = data->NextLiveRange(range->machine_type());
-    DCHECK_NULL(data->live_ranges()[result->vreg()]);
-    data->live_ranges()[result->vreg()] = result;
-
+    if (range->splinter() == nullptr) {
+      TopLevelLiveRange *splinter = data->NextLiveRange(range->machine_type());
+      DCHECK_NULL(data->live_ranges()[splinter->vreg()]);
+      data->live_ranges()[splinter->vreg()] = splinter;
+      range->SetSplinter(splinter);
+    }
     Zone *zone = data->allocation_zone();
-    range->Splinter(start, end, result, zone);
+    range->Splinter(start, end, zone);
   }
 }