[llvm] [CodeGen] Remove static member function Register::virtReg2Index. NFC (PR #127962)

[Matt Arsenault via llvm-commits]

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@@ -77,7 +77,7 @@ static void emitOperand(const MCOperand &Op, SmallVectorImpl<char> &CB) {
   if (Op.isReg()) {
     // Emit the id index starting at 1 (0 is an invalid index).
     support::endian::write<uint32_t>(
-        CB, Register::virtReg2Index(Op.getReg()) + 1, llvm::endianness::little);
+        CB, Register(Op.getReg()).virtRegIndex() + 1, llvm::endianness::little);
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arsenm wrote:

Yes, this is bad 

https://github.com/llvm/llvm-project/pull/127962