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

[Fangrui Song via llvm-commits]

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@@ -137,7 +137,10 @@ template<> struct DenseMapInfo<unsigned long> {
   static inline unsigned long getTombstoneKey() { return ~0UL - 1L; }
 
   static unsigned getHashValue(const unsigned long& Val) {
-    return (unsigned)(Val * 37UL);
+    if constexpr (sizeof(Val) == 4)
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MaskRay wrote:

Now we have `densemap::detail::mix` with very low latency, we can use it unconditionally for now.

https://github.com/llvm/llvm-project/pull/95734