[libc-commits] [libc] [libc][stdlib] Add the FreelistHeap (PR #95066)

[via libc-commits]

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@@ -0,0 +1,189 @@
+//===-- Interface for freelist_heap ---------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDLIB_FREELIST_HEAP_H
+#define LLVM_LIBC_SRC_STDLIB_FREELIST_HEAP_H
+
+#include <stddef.h>
+
+#include "block.h"
+#include "freelist.h"
+#include "src/__support/CPP/optional.h"
+#include "src/__support/CPP/span.h"
+#include "src/string/memory_utils/inline_memcpy.h"
+#include "src/string/memory_utils/inline_memset.h"
+
+namespace LIBC_NAMESPACE {
+
+using cpp::optional;
+using cpp::span;
+
+static constexpr cpp::array<size_t, 6> DEFAULT_BUCKETS{16,  32,  64,
+                                                       128, 256, 512};
+
+template <size_t NUM_BUCKETS = DEFAULT_BUCKETS.size()> class FreeListHeap {
+public:
+  using BlockType = Block<>;
+
+  struct HeapStats {
+    size_t total_bytes;
+    size_t bytes_allocated;
+    size_t cumulative_allocated;
+    size_t cumulative_freed;
+    size_t total_allocate_calls;
+    size_t total_free_calls;
+  };
+  FreeListHeap(span<cpp::byte> region);
+
+  void *allocate(size_t size);
+  void free(void *ptr);
+  void *realloc(void *ptr, size_t size);
+  void *calloc(size_t num, size_t size);
+
+  const HeapStats &heap_stats() const { return heap_stats_; }
+
+private:
+  span<cpp::byte> block_to_span(BlockType *block) {
+    return span<cpp::byte>(block->usable_space(), block->inner_size());
+  }
+
+  void InvalidFreeCrash() { __builtin_trap(); }
+
+  span<cpp::byte> region_;
+  FreeList<NUM_BUCKETS> freelist_;
+  HeapStats heap_stats_;
+};
+
+template <size_t NUM_BUCKETS>
+FreeListHeap<NUM_BUCKETS>::FreeListHeap(span<cpp::byte> region)
+    : region_(region), freelist_(DEFAULT_BUCKETS), heap_stats_() {
+  auto result = BlockType::init(region);
+  BlockType *block = *result;
+
+  freelist_.add_chunk(block_to_span(block));
+
+  heap_stats_.total_bytes = region.size();
+}
+
+template <size_t NUM_BUCKETS>
+void *FreeListHeap<NUM_BUCKETS>::allocate(size_t size) {
+  // Find a chunk in the freelist. Split it if needed, then return
+  auto chunk = freelist_.find_chunk(size);
+
+  if (chunk.data() == nullptr)
+    return nullptr;
+  freelist_.remove_chunk(chunk);
+
+  BlockType *chunk_block = BlockType::from_usable_space(chunk.data());
+
+  // Split that chunk. If there's a leftover chunk, add it to the freelist
+  optional<BlockType *> result = BlockType::split(chunk_block, size);
+  if (result)
+    freelist_.add_chunk(block_to_span(*result));
+
+  chunk_block->mark_used();
+
+  heap_stats_.bytes_allocated += size;
+  heap_stats_.cumulative_allocated += size;
+  heap_stats_.total_allocate_calls += 1;
+
+  return chunk_block->usable_space();
+}
+
+template <size_t NUM_BUCKETS> void FreeListHeap<NUM_BUCKETS>::free(void *ptr) {
+  cpp::byte *bytes = static_cast<cpp::byte *>(ptr);
+
+  if (bytes < region_.data() || bytes >= region_.data() + region_.size()) {
+    InvalidFreeCrash();
----------------
PiJoules wrote:

Done. I believe this is permissible since it's UB if `free` was passed an invalid ptr anyway.

https://github.com/llvm/llvm-project/pull/95066