[llvm] [mlir] eliminating g++ warnings (PR #105520)

[Matt Arsenault via llvm-commits]

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@@ -594,6 +594,8 @@ static bool compareSameArgs(IndexCmpPredicate pred) {
   case IndexCmpPredicate::ULT:
     return false;
   }
+  assert("unknown predicate in compareSameArgs" == nullptr);
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arsenm wrote:

llvm_unreachable, and delete dead return 

https://github.com/llvm/llvm-project/pull/105520