[llvm] [KnownBits] Add reduceUMin/reduceUMax support (PR #211310)

[Simon Pilgrim via llvm-commits]

================
@@ -873,6 +873,50 @@ KnownBits KnownBits::reduceAdd(unsigned NumElts) const {
   return Result;
 }
 
+KnownBits KnownBits::reduceUMin(unsigned NumElts) const {
+  if (NumElts == 0)
+    return KnownBits(getBitWidth());
+
+  unsigned BitWidth = getBitWidth();
+  KnownBits Result(BitWidth);
----------------
RKSimon wrote:

Move the NumElts == 0 case after this and reuse the Result variable:
```
  if (NumElts == 0)
    return Result;
```

https://github.com/llvm/llvm-project/pull/211310