[libc-commits] [libc] [libc] Implement dual freestore rotation for baremetal heap (PR #209811)

[Daniel Thornburgh via libc-commits]

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@@ -68,15 +83,79 @@ class FreeListHeap {
 
   bool is_valid_ptr(const void *ptr) const { return ptr >= begin && ptr < end; }
 
+  /// The store that allocations are served from.
+  LIBC_INLINE FreeStore &active_free_store() { return free_stores[active]; }
+
+  /// @returns The index of the store that receives newly freed blocks. With a
+  /// single free store this is the active store itself, so freed memory is
+  /// immediately available again.
+  LIBC_INLINE size_t quarantine_store_index() const {
+    return (active + 1) % NUM_FREE_STORES;
+  }
+
+  /// @returns Whether `neighbor`, a free block adjacent to a block owned by
+  /// `store_index`, can be merged into it.
+  LIBC_INLINE static bool can_merge(BlockRef neighbor, size_t store_index) {
+    // Blocks too small to be tracked are owned by no store, so they can always
+    // be absorbed. Anything else must belong to the same store: merging across
+    // stores would hand memory quarantined in an inactive store back out
+    // through the active one.
+    return FreeStore::too_small(neighbor) ||
+           neighbor.next().prev_free_store_index() ==
+               static_cast<int>(store_index);
+  }
+
+  /// Marks `block` free, coalesces it with the adjacent free blocks that may
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mysterymath wrote:

This took me a bit to parse: these blocks are already free, right? This just transfers them to the new store. If so, then "Marks `block` free" is *quite* confusing.

https://github.com/llvm/llvm-project/pull/209811