[turbofan] Merge group spill ranges.

src/compiler/greedy-allocator.h

Index: src/compiler/greedy-allocator.h
diff --git a/src/compiler/greedy-allocator.h b/src/compiler/greedy-allocator.h
index 186779b052ae52c6c479366b0474f1a131dca5f1..b7398b38622a1a6855d2dc8935c059015fc264bc 100644
--- a/src/compiler/greedy-allocator.h
+++ b/src/compiler/greedy-allocator.h
@@ -179,6 +179,12 @@ class GreedyAllocator final : public RegisterAllocator {
   // - the portion after the call.
   LiveRange* GetRemainderAfterSplittingAroundFirstCall(LiveRange* range);
 
+  // While we attempt to merge spill ranges later on in the allocation pipeline,
+  // we want to ensure group elements get merged. Waiting until later may hinder
+  // merge-ability, since the pipeline merger (being naive) may create conflicts
+  // between spill ranges of group members.
+  void TryReuseSpillRangesForGroups();
+
   // Necessary heuristic: spill when all else failed.
   void SpillRangeAsLastResort(LiveRange* range);