[llvm] [CodeGen] Use non-static Register::virtRegIndex() instead of static Register::virtReg2Index. NFC (PR #125031)

[Matt Arsenault via llvm-commits]

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@@ -698,7 +698,7 @@ bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
         Def->getParent()->insert(std::next(InsertPos), MI);
       } else
         LLVM_DEBUG(dbgs() << "Dropping debug info for dead vreg"
-                          << Register::virtReg2Index(Reg) << "\n");
+                          << Reg.virtRegIndex() << "\n");
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arsenm wrote:

I wouldn't consider exact debug printing to be F. It should be included for debug log consistency anyway 

https://github.com/llvm/llvm-project/pull/125031