[ADT] Update hash function of uint64_t for DenseMap (#95734)

(Background: See the comment:
https://github.com/llvm/llvm-project/pull/92083#issuecomment-2168121729)

It looks like the hash function for 64bits integers are not very good:

```
  static unsigned getHashValue(const unsigned long long& Val) {
    return (unsigned)(Val * 37ULL);
  }
```

Since the result is truncated to 32 bits. It looks like the higher 32
bits won't contribute to the result. So that `0x1'00000001` will have
the the same results to `0x2'00000001`, `0x3'00000001`, ...

Then we may meet a lot collisions in such cases. I feel it should
generally good to include higher 32 bits for hashing functions.

Not sure who's the appropriate reviewer, adding some people by
impressions.

0 files changed, 0 insertions, 0 deletions