[llvm] [FoldingSet] Switch to linear probing and Algorithm R deletion (PR #218190)

[Fangrui Song via llvm-commits]

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@@ -131,56 +132,23 @@ FoldingSetNodeID::Intern(BumpPtrAllocator &Allocator) const {
 }
 
 //===----------------------------------------------------------------------===//
-/// Helper functions for FoldingSetBase.
-
-/// GetNextPtr - In order to save space, each bucket is a
-/// singly-linked-list. In order to make deletion more efficient, we make
-/// the list circular, so we can delete a node without computing its hash.
-/// The problem with this is that the start of the hash buckets are not
-/// Nodes. If NextInBucketPtr is a bucket pointer, this method returns null:
-/// use GetBucketPtr when this happens.
-static FoldingSetBase::Node *GetNextPtr(void *NextInBucketPtr) {
-  // The low bit is set if this is the pointer back to the bucket.
-  if (reinterpret_cast<intptr_t>(NextInBucketPtr) & 1)
-    return nullptr;
-
-  return static_cast<FoldingSetBase::Node *>(NextInBucketPtr);
-}
-
-/// GetBucketPtr - Provides a casting of a bucket pointer for isNode
-/// testing.
-static void **GetBucketPtr(void *NextInBucketPtr) {
-  intptr_t Ptr = reinterpret_cast<intptr_t>(NextInBucketPtr);
-  assert((Ptr & 1) && "Not a bucket pointer");
-  return reinterpret_cast<void **>(Ptr & ~intptr_t(1));
-}
+// FoldingSetBase Implementation
 
-/// GetBucketFor - Hash the specified node ID and return the hash bucket for
-/// the specified ID.
-static void **GetBucketFor(unsigned Hash, void **Buckets, unsigned NumBuckets) {
-  // NumBuckets is always a power of 2.
-  unsigned BucketNum = Hash & (NumBuckets - 1);
-  return Buckets + BucketNum;
+/// Encode a hash as the token FindNodeOrInsertPos hands back. Never null, and
+/// unlike a bucket address it survives intervening insertions.
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MaskRay wrote:

Simplified comment

https://github.com/llvm/llvm-project/pull/218190