[llvm] [SimplifyCFG] Fix Missing Case Computation for Arbitrary Width Integers (PR #77831)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

I don't think it is worth handing `switch i128` cases.
We can early exit if the bit width of condition value is larger than 64:
```
  auto *CondTy = cast<IntegerType>(SI->getCondition()->getType());
  if (CondTy->getIntegerBitWidth() > 64 ||
      !DL.fitsInLegalInteger(CondTy->getIntegerBitWidth()))
    return false;
```

https://github.com/llvm/llvm-project/pull/77831