[llvm] [SelectionDAG] Switch to LiveRegUnits (PR #84197)

[Matt Arsenault via llvm-commits]

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@@ -1113,7 +1113,7 @@ static void toggleKills(const MachineRegisterInfo &MRI, LivePhysRegs &LiveRegs,
       continue;
 
     // Things that are available after the instruction are killed by it.
-    bool IsKill = LiveRegs.available(MRI, Reg);
+    bool IsKill = LiveRegs.available(Reg);
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arsenm wrote:

Shouldn't set kill on reserved registers, although you might need an additional check. I think it would be best if the verifier didn't allow it 

https://github.com/llvm/llvm-project/pull/84197