[llvm] [LiveIns] Improve recomputeLiveIns() (PR #88951)

[Nikita Popov via llvm-commits]

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@@ -477,7 +481,7 @@ class MachineBasicBlock
   /// Remove entry from the livein set and return iterator to the next.
   livein_iterator removeLiveIn(livein_iterator I);
 
-  std::vector<RegisterMaskPair> getLiveIns() const { return LiveIns; }
+  const std::vector<RegisterMaskPair> getLiveIns() const { return LiveIns; }
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nikic wrote:

Was this supposed to be?
```suggestion
  const std::vector<RegisterMaskPair> &getLiveIns() const { return LiveIns; }
```

https://github.com/llvm/llvm-project/pull/88951