[llvm] [AMDGPU] Update LiveVariables in SILowerControlFlow::combineMasks (PR #217844)

[Arseniy Obolenskiy via llvm-commits]

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@@ -636,10 +638,29 @@ void SILowerControlFlow::combineMasks(MachineInstr &MI) {
     return;
 
   Register Reg = MI.getOperand(OpToReplace).getReg();
+  MachineInstr *Def = MRI->getUniqueVRegDef(Reg);
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aobolensk wrote:

Ah, yes, I have not found the case when it is possible, let's add an assert then

https://github.com/llvm/llvm-project/pull/217844