[llvm] [TableGen] Rework error reporting for duplicate Feature/Processor. (PR #102257)

[Rahul Joshi via llvm-commits]

jurahul wrote:

> > Could you use line number as the tie breaker in the sort?
> 
> I did look into whether I can order them by `SMLoc` but did not find a way. Let me take a closer look.

It seems this works:


```
  auto GetSourceLocation = [](const Record *Rec) {
    const SMLoc Loc = Rec->getLoc()[0];
     const MemoryBuffer *MB =
        SrcMgr.getMemoryBuffer(SrcMgr.FindBufferContainingLoc(Loc));
    StringRef BufferID = MB->getBufferIdentifier();
    auto LineAndCol = SrcMgr.getLineAndColumn(Loc);
    return std::tuple(BufferID, LineAndCol.first, LineAndCol.second);
  };

  // Order First/Second by their lexical order if possible. Note that if they
  // are from different files, they will be ordered by file names. 
  if (GetSourceLocation(First) > GetSourceLocation(Second))
    std::swap(First, Second);
```

right before printing the error message. It's still not foolproof since it uses filename as the first key, so if fileA included fileB, I am assuming it will think fileA is the earlier def and one in fileB is second, so I am still keeping the message position ambiguous. The !/$ for getting this fully correct is not there. I'll update the PR soon.

https://github.com/llvm/llvm-project/pull/102257