[libc][stdlib] Add the FreelistHeap (#95066)

This is the actual freelist allocator which utilizes the generic
FreeList and the Block classes. We will eventually wrap the malloc
interface around this.

This is a part of #94270 to land in smaller patches.

2 files changed, 252 insertions, 0 deletions

diff --git a/libc/test/src/stdlib/CMakeLists.txt b/libc/test/src/stdlib/CMakeLists.txt
index d3954f0..f3033a4 100644
--- a/libc/test/src/stdlib/CMakeLists.txt
+++ b/libc/test/src/stdlib/CMakeLists.txt
@@ -79,6 +79,19 @@ add_libc_test(
     libc.src.__support.CPP.span
 )
 
+add_libc_test(
+  freelist_heap_test
+  SUITE
+    libc-stdlib-tests
+  SRCS
+    freelist_heap_test.cpp
+  DEPENDS
+    libc.src.__support.CPP.span
+    libc.src.stdlib.freelist_heap
+    libc.src.string.memcmp
+    libc.src.string.memcpy
+)
+
 add_fp_unittest(
   strtod_test
   SUITE
diff --git a/libc/test/src/stdlib/freelist_heap_test.cpp b/libc/test/src/stdlib/freelist_heap_test.cpp
new file mode 100644
index 0000000..b89f47f
--- /dev/null
+++ b/libc/test/src/stdlib/freelist_heap_test.cpp
@@ -0,0 +1,239 @@
+//===-- Unittests 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/span.h"
+#include "src/stdlib/freelist_heap.h"
+#include "src/string/memcmp.h"
+#include "src/string/memcpy.h"
+#include "test/UnitTest/Test.h"
+
+namespace LIBC_NAMESPACE {
+
+TEST(LlvmLibcFreeListHeap, CanAllocate) {
+  constexpr size_t N = 2048;
+  constexpr size_t ALLOC_SIZE = 512;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(0)};
+
+  FreeListHeap<> allocator(buf);
+
+  void *ptr = allocator.allocate(ALLOC_SIZE);
+
+  ASSERT_NE(ptr, static_cast<void *>(nullptr));
+  // In this case, the allocator should be returning us the start of the chunk.
+  EXPECT_EQ(ptr, static_cast<void *>(
+                     &buf[0] + FreeListHeap<>::BlockType::BLOCK_OVERHEAD));
+}
+
+TEST(LlvmLibcFreeListHeap, AllocationsDontOverlap) {
+  constexpr size_t N = 2048;
+  constexpr size_t ALLOC_SIZE = 512;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(0)};
+
+  FreeListHeap<> allocator(buf);
+
+  void *ptr1 = allocator.allocate(ALLOC_SIZE);
+  void *ptr2 = allocator.allocate(ALLOC_SIZE);
+
+  ASSERT_NE(ptr1, static_cast<void *>(nullptr));
+  ASSERT_NE(ptr2, static_cast<void *>(nullptr));
+
+  uintptr_t ptr1_start = reinterpret_cast<uintptr_t>(ptr1);
+  uintptr_t ptr1_end = ptr1_start + ALLOC_SIZE;
+  uintptr_t ptr2_start = reinterpret_cast<uintptr_t>(ptr2);
+
+  EXPECT_GT(ptr2_start, ptr1_end);
+}
+
+TEST(LlvmLibcFreeListHeap, CanFreeAndRealloc) {
+  // There's not really a nice way to test that free works, apart from to try
+  // and get that value back again.
+  constexpr size_t N = 2048;
+  constexpr size_t ALLOC_SIZE = 512;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(0)};
+
+  FreeListHeap<> allocator(buf);
+
+  void *ptr1 = allocator.allocate(ALLOC_SIZE);
+  allocator.free(ptr1);
+  void *ptr2 = allocator.allocate(ALLOC_SIZE);
+
+  EXPECT_EQ(ptr1, ptr2);
+}
+
+TEST(LlvmLibcFreeListHeap, ReturnsNullWhenAllocationTooLarge) {
+  constexpr size_t N = 2048;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(0)};
+
+  FreeListHeap<> allocator(buf);
+
+  EXPECT_EQ(allocator.allocate(N), static_cast<void *>(nullptr));
+}
+
+TEST(LlvmLibcFreeListHeap, ReturnsNullWhenFull) {
+  constexpr size_t N = 2048;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(0)};
+
+  FreeListHeap<> allocator(buf);
+
+  EXPECT_NE(allocator.allocate(N - FreeListHeap<>::BlockType::BLOCK_OVERHEAD),
+            static_cast<void *>(nullptr));
+  EXPECT_EQ(allocator.allocate(1), static_cast<void *>(nullptr));
+}
+
+TEST(LlvmLibcFreeListHeap, ReturnedPointersAreAligned) {
+  constexpr size_t N = 2048;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(0)};
+
+  FreeListHeap<> allocator(buf);
+
+  void *ptr1 = allocator.allocate(1);
+
+  // Should be aligned to native pointer alignment
+  uintptr_t ptr1_start = reinterpret_cast<uintptr_t>(ptr1);
+  size_t alignment = alignof(void *);
+
+  EXPECT_EQ(ptr1_start % alignment, static_cast<size_t>(0));
+
+  void *ptr2 = allocator.allocate(1);
+  uintptr_t ptr2_start = reinterpret_cast<uintptr_t>(ptr2);
+
+  EXPECT_EQ(ptr2_start % alignment, static_cast<size_t>(0));
+}
+
+TEST(LlvmLibcFreeListHeap, CanRealloc) {
+  constexpr size_t N = 2048;
+  constexpr size_t ALLOC_SIZE = 512;
+  constexpr size_t kNewAllocSize = 768;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(1)};
+
+  FreeListHeap<> allocator(buf);
+
+  void *ptr1 = allocator.allocate(ALLOC_SIZE);
+  void *ptr2 = allocator.realloc(ptr1, kNewAllocSize);
+
+  ASSERT_NE(ptr1, static_cast<void *>(nullptr));
+  ASSERT_NE(ptr2, static_cast<void *>(nullptr));
+}
+
+TEST(LlvmLibcFreeListHeap, ReallocHasSameContent) {
+  constexpr size_t N = 2048;
+  constexpr size_t ALLOC_SIZE = sizeof(int);
+  constexpr size_t kNewAllocSize = sizeof(int) * 2;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(1)};
+  // Data inside the allocated block.
+  cpp::byte data1[ALLOC_SIZE];
+  // Data inside the reallocated block.
+  cpp::byte data2[ALLOC_SIZE];
+
+  FreeListHeap<> allocator(buf);
+
+  int *ptr1 = reinterpret_cast<int *>(allocator.allocate(ALLOC_SIZE));
+  *ptr1 = 42;
+  memcpy(data1, ptr1, ALLOC_SIZE);
+  int *ptr2 = reinterpret_cast<int *>(allocator.realloc(ptr1, kNewAllocSize));
+  memcpy(data2, ptr2, ALLOC_SIZE);
+
+  ASSERT_NE(ptr1, static_cast<int *>(nullptr));
+  ASSERT_NE(ptr2, static_cast<int *>(nullptr));
+  // Verify that data inside the allocated and reallocated chunks are the same.
+  EXPECT_EQ(LIBC_NAMESPACE::memcmp(data1, data2, ALLOC_SIZE), 0);
+}
+
+TEST(LlvmLibcFreeListHeap, ReturnsNullReallocFreedPointer) {
+  constexpr size_t N = 2048;
+  constexpr size_t ALLOC_SIZE = 512;
+  constexpr size_t kNewAllocSize = 256;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(0)};
+
+  FreeListHeap<> allocator(buf);
+
+  void *ptr1 = allocator.allocate(ALLOC_SIZE);
+  allocator.free(ptr1);
+  void *ptr2 = allocator.realloc(ptr1, kNewAllocSize);
+
+  EXPECT_EQ(static_cast<void *>(nullptr), ptr2);
+}
+
+TEST(LlvmLibcFreeListHeap, ReallocSmallerSize) {
+  constexpr size_t N = 2048;
+  constexpr size_t ALLOC_SIZE = 512;
+  constexpr size_t kNewAllocSize = 256;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(0)};
+
+  FreeListHeap<> allocator(buf);
+
+  void *ptr1 = allocator.allocate(ALLOC_SIZE);
+  void *ptr2 = allocator.realloc(ptr1, kNewAllocSize);
+
+  // For smaller sizes, realloc will not shrink the block.
+  EXPECT_EQ(ptr1, ptr2);
+}
+
+TEST(LlvmLibcFreeListHeap, ReallocTooLarge) {
+  constexpr size_t N = 2048;
+  constexpr size_t ALLOC_SIZE = 512;
+  constexpr size_t kNewAllocSize = 4096;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(0)};
+
+  FreeListHeap<> allocator(buf);
+
+  void *ptr1 = allocator.allocate(ALLOC_SIZE);
+  void *ptr2 = allocator.realloc(ptr1, kNewAllocSize);
+
+  // realloc() will not invalidate the original pointer if realloc() fails
+  EXPECT_NE(static_cast<void *>(nullptr), ptr1);
+  EXPECT_EQ(static_cast<void *>(nullptr), ptr2);
+}
+
+TEST(LlvmLibcFreeListHeap, CanCalloc) {
+  constexpr size_t N = 2048;
+  constexpr size_t ALLOC_SIZE = 128;
+  constexpr size_t kNum = 4;
+  constexpr int size = kNum * ALLOC_SIZE;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(1)};
+  constexpr cpp::byte zero{0};
+
+  FreeListHeap<> allocator(buf);
+
+  cpp::byte *ptr1 =
+      reinterpret_cast<cpp::byte *>(allocator.calloc(kNum, ALLOC_SIZE));
+
+  // calloc'd content is zero.
+  for (int i = 0; i < size; i++)
+    EXPECT_EQ(ptr1[i], zero);
+}
+
+TEST(LlvmLibcFreeListHeap, CanCallocWeirdSize) {
+  constexpr size_t N = 2048;
+  constexpr size_t ALLOC_SIZE = 143;
+  constexpr size_t kNum = 3;
+  constexpr int size = kNum * ALLOC_SIZE;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(132)};
+  constexpr cpp::byte zero{0};
+
+  FreeListHeap<> allocator(buf);
+
+  cpp::byte *ptr1 =
+      reinterpret_cast<cpp::byte *>(allocator.calloc(kNum, ALLOC_SIZE));
+
+  // calloc'd content is zero.
+  for (int i = 0; i < size; i++)
+    EXPECT_EQ(ptr1[i], zero);
+}
+
+TEST(LlvmLibcFreeListHeap, CallocTooLarge) {
+  constexpr size_t N = 2048;
+  constexpr size_t ALLOC_SIZE = 2049;
+  alignas(FreeListHeap<>::BlockType) cpp::byte buf[N] = {cpp::byte(1)};
+
+  FreeListHeap<> allocator(buf);
+
+  EXPECT_EQ(allocator.calloc(1, ALLOC_SIZE), static_cast<void *>(nullptr));
+}
+
+} // namespace LIBC_NAMESPACE