[llvm] [MachineLoopInfo] Fix assertion failure on undef use operands (PR #100137)

[Matt Arsenault via llvm-commits]

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@@ -287,7 +287,7 @@ bool MachineLoop::isLoopInvariant(MachineInstr &I,
       }
     }
 
-    if (!MO.isUse())
+    if (!MO.readsReg())
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arsenm wrote:

this needs a mir test too 

https://github.com/llvm/llvm-project/pull/100137