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

[Fangrui Song via llvm-commits]

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@@ -207,145 +175,110 @@ FoldingSetBase::~FoldingSetBase() { free(Buckets); }
 
 void FoldingSetBase::clear() {
   incrementEpoch();
-  // Set all but the last bucket to null pointers.
-  memset(Buckets, 0, NumBuckets * sizeof(void *));
-
-  // Set the very last bucket to be a non-null "pointer".
-  Buckets[NumBuckets] = reinterpret_cast<void *>(-1);
-
-  // Reset the node count to zero.
+  // Stale hashes are unreachable, so only the occupancy needs resetting.
+  if (NumBuckets)
+    memset(Buckets, 0, NumBuckets * sizeof(void *));
   NumNodes = 0;
 }
 
-void FoldingSetBase::GrowBucketCount(unsigned NewBucketCount,
-                                     const FoldingSetInfo &Info) {
-  assert((NewBucketCount > NumBuckets) &&
-         "Can't shrink a folding set with GrowBucketCount");
-  assert(isPowerOf2_32(NewBucketCount) && "Bad bucket count!");
+void FoldingSetBase::placeNode(Node *N, uint32_t Hash) {
+  unsigned Mask = NumBuckets - 1;
+  unsigned I = Hash & Mask;
+  while (Buckets[I]) {
+    // A second copy of N hashes here too, so the probe always passes it.
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MaskRay wrote:

Deleted 

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