[llvm] [TableGen] Complete the support for artificial registers (PR #183371)

[Mikael Holmen via llvm-commits]

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@@ -2444,6 +2488,8 @@ void CodeGenRegBank::inferMatchingSuperRegClass(
     TopoSigs.reset();
     for (const CodeGenRegister *Super : RC->getMembers()) {
       const CodeGenRegister *Sub = Super->getSubRegs().find(SubIdx)->second;
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mikaelholmen wrote:

I've verified that the
```Error: attempt to dereference a past-the-end iterator.```
error goes away if we move the Artificial bail out before the call to find.

https://github.com/llvm/llvm-project/pull/183371