[llvm] [Instrumentation] Support verifying machine function (PR #90931)

[Matt Arsenault via llvm-commits]

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@@ -362,6 +363,14 @@ class TriggerVerifierErrorPass
     return PreservedAnalyses::none();
   }
 
+  PreservedAnalyses run(MachineFunction &MF, MachineFunctionAnalysisManager &) {
+    // Intentionally create a virtual register and set NoVRegs property.
+    auto &MRI = MF.getRegInfo();
+    MRI.createGenericVirtualRegister(LLT::scalar(8));
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arsenm wrote:

To be safe, it would be best to introduce an actual instruction with the register. IIRC we permit virtual registers that have no uses in the MIR 

https://github.com/llvm/llvm-project/pull/90931