[llvm] [RegAlloc] Account for use availability when applying rematerializable weight discount (PR #159180)

[Matt Arsenault via llvm-commits]

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@@ -466,6 +466,10 @@ class LiveIntervals {
   /// have any segments or value numbers.
   LLVM_ABI void constructMainRangeFromSubranges(LiveInterval &LI);
 
+  /// \returns true if all registers used by \p OrigMI at \p OrigIdx are also
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arsenm wrote:

The consistent thing would be to use SlotIndex arguments 

https://github.com/llvm/llvm-project/pull/159180