[llvm] [CodeGen] Fix stale LiveIntervals regmask tables after MachineBasicBl… (PR #209610)

[Nathan Corbyn via llvm-commits]

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@@ -482,6 +492,20 @@ class LiveIntervals {
   /// Compute RegMaskSlots and RegMaskBits.
   void computeRegMasks();
 
+  /// Shared implementation of insertMBBInMaps(). \p AssumeRegMaskEmpty is true
+  /// for every caller but splitAt(), which legitimately inserts a block already
+  /// populated with regmask-bearing instructions and fixes up the regmask
+  /// slices afterward via reassignRegMaskSlots(). When it is true \p MBB must
+  /// contain no regmask operands.
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cofibrant wrote:

This comment wants updating

https://github.com/llvm/llvm-project/pull/209610