libc/test/src/__support/block_test.cpp - llvm-project - Git at Google

 //===-- Unittests for a block of memory -------------------------*- C++ -*-===//
 //
 // 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 <stddef.h>

 #include "src/__support/CPP/array.h"
 #include "src/__support/CPP/bit.h"
 #include "src/__support/CPP/span.h"
 #include "src/__support/block.h"
 #include "src/string/memcpy.h"
 #include "test/UnitTest/Test.h"

 using LIBC_NAMESPACE::Block;
 using LIBC_NAMESPACE::cpp::array;
 using LIBC_NAMESPACE::cpp::bit_ceil;
 using LIBC_NAMESPACE::cpp::byte;
 using LIBC_NAMESPACE::cpp::span;

 TEST(LlvmLibcBlockTest, CanCreateSingleAlignedBlock) {
   constexpr size_t kN = 1024;
   alignas(max_align_t) array<byte, kN> bytes;

   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block = *result;

   EXPECT_EQ(reinterpret_cast<uintptr_t>(block) % alignof(Block), size_t{0});
   EXPECT_TRUE(block->is_usable_space_aligned(alignof(max_align_t)));

   Block *last = block->next();
   ASSERT_NE(last, static_cast<Block *>(nullptr));
   EXPECT_EQ(reinterpret_cast<uintptr_t>(last) % alignof(Block), size_t{0});

   EXPECT_EQ(last->outer_size(), sizeof(Block));
   EXPECT_EQ(last->prev_free(), block);
   EXPECT_TRUE(last->used());

   size_t block_outer_size =
       reinterpret_cast<uintptr_t>(last) - reinterpret_cast<uintptr_t>(block);
   EXPECT_EQ(block->outer_size(), block_outer_size);
   EXPECT_EQ(block->inner_size(),
             block_outer_size - sizeof(Block) + Block::PREV_FIELD_SIZE);
   EXPECT_EQ(block->prev_free(), static_cast<Block *>(nullptr));
   EXPECT_FALSE(block->used());
 }

 TEST(LlvmLibcBlockTest, CanCreateUnalignedSingleBlock) {
   constexpr size_t kN = 1024;

   // Force alignment, so we can un-force it below
   alignas(max_align_t) array<byte, kN> bytes;
   span<byte> aligned(bytes);

   auto result = Block::init(aligned.subspan(1));
   EXPECT_TRUE(result.has_value());

   Block *block = *result;
   EXPECT_EQ(reinterpret_cast<uintptr_t>(block) % alignof(Block), size_t{0});
   EXPECT_TRUE(block->is_usable_space_aligned(alignof(max_align_t)));

   Block *last = block->next();
   ASSERT_NE(last, static_cast<Block *>(nullptr));
   EXPECT_EQ(reinterpret_cast<uintptr_t>(last) % alignof(Block), size_t{0});
 }

 TEST(LlvmLibcBlockTest, CannotCreateTooSmallBlock) {
   array<byte, 2> bytes;
   auto result = Block::init(bytes);
   EXPECT_FALSE(result.has_value());
 }

 TEST(LlvmLibcBlockTest, CanSplitBlock) {
   constexpr size_t kN = 1024;

   // Choose a split position such that the next block's usable space is 512
   // bytes from this one's. This should be sufficient for any machine's
   // alignment.
   const size_t kSplitN = Block::inner_size(512);

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   auto *block1 = *result;
   size_t orig_size = block1->outer_size();

   result = block1->split(kSplitN);
   ASSERT_TRUE(result.has_value());
   auto *block2 = *result;

   EXPECT_EQ(block1->inner_size(), kSplitN);
   EXPECT_EQ(block1->outer_size(),
             kSplitN - Block::PREV_FIELD_SIZE + sizeof(Block));

   EXPECT_EQ(block2->outer_size(), orig_size - block1->outer_size());
   EXPECT_FALSE(block2->used());
   EXPECT_EQ(reinterpret_cast<uintptr_t>(block2) % alignof(Block), size_t{0});
   EXPECT_TRUE(block2->is_usable_space_aligned(alignof(max_align_t)));

   EXPECT_EQ(block1->next(), block2);
   EXPECT_EQ(block2->prev_free(), block1);
 }

 TEST(LlvmLibcBlockTest, CanSplitBlockUnaligned) {
   constexpr size_t kN = 1024;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block1 = *result;
   size_t orig_size = block1->outer_size();

   constexpr size_t kSplitN = 513;

   result = block1->split(kSplitN);
   ASSERT_TRUE(result.has_value());
   Block *block2 = *result;

   EXPECT_GE(block1->inner_size(), kSplitN);

   EXPECT_EQ(block2->outer_size(), orig_size - block1->outer_size());
   EXPECT_FALSE(block2->used());
   EXPECT_EQ(reinterpret_cast<uintptr_t>(block2) % alignof(Block), size_t{0});
   EXPECT_TRUE(block2->is_usable_space_aligned(alignof(max_align_t)));

   EXPECT_EQ(block1->next(), block2);
   EXPECT_EQ(block2->prev_free(), block1);
 }

 TEST(LlvmLibcBlockTest, CanSplitMidBlock) {
   // split once, then split the original block again to ensure that the
   // pointers get rewired properly.
   // I.e.
   // [[             BLOCK 1            ]]
   // block1->split()
   // [[       BLOCK1       ]][[ BLOCK2 ]]
   // block1->split()
   // [[ BLOCK1 ]][[ BLOCK3 ]][[ BLOCK2 ]]

   constexpr size_t kN = 1024;
   constexpr size_t kSplit1 = 512;
   constexpr size_t kSplit2 = 256;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block1 = *result;

   result = block1->split(kSplit1);
   ASSERT_TRUE(result.has_value());
   Block *block2 = *result;

   result = block1->split(kSplit2);
   ASSERT_TRUE(result.has_value());
   Block *block3 = *result;

   EXPECT_EQ(block1->next(), block3);
   EXPECT_EQ(block3->prev_free(), block1);
   EXPECT_EQ(block3->next(), block2);
   EXPECT_EQ(block2->prev_free(), block3);
 }

 TEST(LlvmLibcBlockTest, CannotSplitTooSmallBlock) {
   constexpr size_t kN = 64;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block = *result;

   result = block->split(block->inner_size() + 1);
   ASSERT_FALSE(result.has_value());
 }

 TEST(LlvmLibcBlockTest, CannotSplitBlockWithoutHeaderSpace) {
   constexpr size_t kN = 1024;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block = *result;

   result = block->split(block->inner_size() - sizeof(Block) + 1);
   ASSERT_FALSE(result.has_value());
 }

 TEST(LlvmLibcBlockTest, CannotMakeBlockLargerInSplit) {
   // Ensure that we can't ask for more space than the block actually has...
   constexpr size_t kN = 1024;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block = *result;

   result = block->split(block->inner_size() + 1);
   ASSERT_FALSE(result.has_value());
 }

 TEST(LlvmLibcBlockTest, CanMakeMinimalSizeFirstBlock) {
   // This block does support splitting with minimal payload size.
   constexpr size_t kN = 1024;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block = *result;

   result = block->split(0);
   ASSERT_TRUE(result.has_value());
   EXPECT_LE(block->outer_size(), sizeof(Block) + alignof(max_align_t));
 }

 TEST(LlvmLibcBlockTest, CanMakeMinimalSizeSecondBlock) {
   // Likewise, the split block can be minimal-width.
   constexpr size_t kN = 1024;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block1 = *result;

   result = block1->split(Block::prev_possible_block_start(
                              reinterpret_cast<uintptr_t>(block1->next())) -
                          reinterpret_cast<uintptr_t>(block1->usable_space()) +
                          Block::PREV_FIELD_SIZE);
   ASSERT_TRUE(result.has_value());
   EXPECT_LE((*result)->outer_size(), sizeof(Block) + alignof(max_align_t));
 }

 TEST(LlvmLibcBlockTest, CanMarkBlockUsed) {
   constexpr size_t kN = 1024;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block = *result;
   size_t orig_size = block->outer_size();

   block->mark_used();
   EXPECT_TRUE(block->used());
   EXPECT_EQ(block->outer_size(), orig_size);

   block->mark_free();
   EXPECT_FALSE(block->used());
 }

 TEST(LlvmLibcBlockTest, CannotSplitUsedBlock) {
   constexpr size_t kN = 1024;
   constexpr size_t kSplitN = 512;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block = *result;

   block->mark_used();
   result = block->split(kSplitN);
   ASSERT_FALSE(result.has_value());
 }

 TEST(LlvmLibcBlockTest, CanMergeWithNextBlock) {
   // Do the three way merge from "CanSplitMidBlock", and let's
   // merge block 3 and 2
   constexpr size_t kN = 1024;
   constexpr size_t kSplit1 = 512;
   constexpr size_t kSplit2 = 256;
   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block1 = *result;
   size_t total_size = block1->outer_size();

   result = block1->split(kSplit1);
   ASSERT_TRUE(result.has_value());

   result = block1->split(kSplit2);
   size_t block1_size = block1->outer_size();
   ASSERT_TRUE(result.has_value());
   Block *block3 = *result;

   EXPECT_TRUE(block3->merge_next());

   EXPECT_EQ(block1->next(), block3);
   EXPECT_EQ(block3->prev_free(), block1);
   EXPECT_EQ(block1->outer_size(), block1_size);
   EXPECT_EQ(block3->outer_size(), total_size - block1->outer_size());
 }

 TEST(LlvmLibcBlockTest, CannotMergeWithFirstOrLastBlock) {
   constexpr size_t kN = 1024;
   constexpr size_t kSplitN = 512;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block1 = *result;

   // Do a split, just to check that the checks on next/prev are different...
   result = block1->split(kSplitN);
   ASSERT_TRUE(result.has_value());
   Block *block2 = *result;

   EXPECT_FALSE(block2->merge_next());
 }

 TEST(LlvmLibcBlockTest, CannotMergeUsedBlock) {
   constexpr size_t kN = 1024;
   constexpr size_t kSplitN = 512;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block = *result;

   // Do a split, just to check that the checks on next/prev are different...
   result = block->split(kSplitN);
   ASSERT_TRUE(result.has_value());

   block->mark_used();
   EXPECT_FALSE(block->merge_next());
 }

 TEST(LlvmLibcBlockTest, CanGetBlockFromUsableSpace) {
   array<byte, 1024> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block1 = *result;

   void *ptr = block1->usable_space();
   Block *block2 = Block::from_usable_space(ptr);
   EXPECT_EQ(block1, block2);
 }

 TEST(LlvmLibcBlockTest, CanGetConstBlockFromUsableSpace) {
   constexpr size_t kN = 1024;

   array<byte, kN> bytes{};
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   const Block *block1 = *result;

   const void *ptr = block1->usable_space();
   const Block *block2 = Block::from_usable_space(ptr);
   EXPECT_EQ(block1, block2);
 }

 TEST(LlvmLibcBlockTest, Allocate) {
   constexpr size_t kN = 1024;

   // Ensure we can allocate everything up to the block size within this block.
   for (size_t i = 0; i < kN; ++i) {
     array<byte, kN> bytes;
     auto result = Block::init(bytes);
     ASSERT_TRUE(result.has_value());
     Block *block = *result;

     if (i > block->inner_size())
       continue;

     auto info = Block::allocate(block, alignof(max_align_t), i);
     EXPECT_NE(info.block, static_cast<Block *>(nullptr));
   }

   // Ensure we can allocate a byte at every guaranteeable alignment.
   for (size_t i = 1; i < kN / alignof(max_align_t); ++i) {
     array<byte, kN> bytes;
     auto result = Block::init(bytes);
     ASSERT_TRUE(result.has_value());
     Block *block = *result;

     size_t alignment = i * alignof(max_align_t);
     if (Block::min_size_for_allocation(alignment, 1) > block->inner_size())
       continue;

     auto info = Block::allocate(block, alignment, 1);
     EXPECT_NE(info.block, static_cast<Block *>(nullptr));
   }
 }

 TEST(LlvmLibcBlockTest, AllocateAlreadyAligned) {
   constexpr size_t kN = 1024;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block = *result;
   uintptr_t orig_end = reinterpret_cast<uintptr_t>(block) + block->outer_size();

   constexpr size_t SIZE = Block::PREV_FIELD_SIZE + 1;

   auto [aligned_block, prev, next] =
       Block::allocate(block, alignof(max_align_t), SIZE);

   // Since this is already aligned, there should be no previous block.
   EXPECT_EQ(prev, static_cast<Block *>(nullptr));

   // Ensure we the block is aligned and large enough.
   EXPECT_NE(aligned_block, static_cast<Block *>(nullptr));
   EXPECT_TRUE(aligned_block->is_usable_space_aligned(alignof(max_align_t)));
   EXPECT_GE(aligned_block->inner_size(), SIZE);

   // Check the next block.
   EXPECT_NE(next, static_cast<Block *>(nullptr));
   EXPECT_EQ(aligned_block->next(), next);
   EXPECT_EQ(reinterpret_cast<uintptr_t>(next) + next->outer_size(), orig_end);
 }

 TEST(LlvmLibcBlockTest, AllocateNeedsAlignment) {
   constexpr size_t kN = 1024;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block = *result;

   uintptr_t orig_end = reinterpret_cast<uintptr_t>(block) + block->outer_size();

   // Now pick an alignment such that the usable space is not already aligned to
   // it. We want to explicitly test that the block will split into one before
   // it.
   size_t alignment = alignof(max_align_t);
   while (block->is_usable_space_aligned(alignment))
     alignment += alignof(max_align_t);

   auto [aligned_block, prev, next] = Block::allocate(block, alignment, 10);

   // Check the previous block was created appropriately. Since this block is the
   // first block, a new one should be made before this.
   EXPECT_NE(prev, static_cast<Block *>(nullptr));
   EXPECT_EQ(aligned_block->prev_free(), prev);
   EXPECT_EQ(prev->next(), aligned_block);
   EXPECT_EQ(prev->outer_size(), reinterpret_cast<uintptr_t>(aligned_block) -
                                     reinterpret_cast<uintptr_t>(prev));

   // Ensure we the block is aligned and the size we expect.
   EXPECT_NE(next, static_cast<Block *>(nullptr));
   EXPECT_TRUE(aligned_block->is_usable_space_aligned(alignment));

   // Check the next block.
   EXPECT_NE(next, static_cast<Block *>(nullptr));
   EXPECT_EQ(aligned_block->next(), next);
   EXPECT_EQ(reinterpret_cast<uintptr_t>(next) + next->outer_size(), orig_end);
 }

 TEST(LlvmLibcBlockTest, PreviousBlockMergedIfNotFirst) {
   constexpr size_t kN = 1024;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block = *result;

   // Split the block roughly halfway and work on the second half.
   auto result2 = block->split(kN / 2);
   ASSERT_TRUE(result2.has_value());
   Block *newblock = *result2;
   ASSERT_EQ(newblock->prev_free(), block);
   size_t old_prev_size = block->outer_size();

   // Now pick an alignment such that the usable space is not already aligned to
   // it. We want to explicitly test that the block will split into one before
   // it.
   size_t alignment = alignof(max_align_t);
   while (newblock->is_usable_space_aligned(alignment))
     alignment += alignof(max_align_t);

   // Ensure we can allocate in the new block.
   auto [aligned_block, prev, next] = Block::allocate(newblock, alignment, 1);

   // Now there should be no new previous block. Instead, the padding we did
   // create should be merged into the original previous block.
   EXPECT_EQ(prev, static_cast<Block *>(nullptr));
   EXPECT_EQ(aligned_block->prev_free(), block);
   EXPECT_EQ(block->next(), aligned_block);
   EXPECT_GT(block->outer_size(), old_prev_size);
 }

 TEST(LlvmLibcBlockTest, CanRemergeBlockAllocations) {
   // Finally to ensure we made the split blocks correctly via allocate. We
   // should be able to reconstruct the original block from the blocklets.
   //
   // This is the same setup as with the `AllocateNeedsAlignment` test case.
   constexpr size_t kN = 1024;

   array<byte, kN> bytes;
   auto result = Block::init(bytes);
   ASSERT_TRUE(result.has_value());
   Block *block = *result;

   Block *orig_block = block;
   size_t orig_size = orig_block->outer_size();

   Block *last = block->next();

   ASSERT_EQ(block->prev_free(), static_cast<Block *>(nullptr));

   // Now pick an alignment such that the usable space is not already aligned to
   // it. We want to explicitly test that the block will split into one before
   // it.
   size_t alignment = alignof(max_align_t);
   while (block->is_usable_space_aligned(alignment))
     alignment += alignof(max_align_t);

   auto [aligned_block, prev, next] = Block::allocate(block, alignment, 1);

   // Check we have the appropriate blocks.
   ASSERT_NE(prev, static_cast<Block *>(nullptr));
   ASSERT_EQ(aligned_block->prev_free(), prev);
   EXPECT_NE(next, static_cast<Block *>(nullptr));
   EXPECT_EQ(aligned_block->next(), next);
   EXPECT_EQ(next->next(), last);

   // Now check for successful merges.
   EXPECT_TRUE(prev->merge_next());
   EXPECT_EQ(prev->next(), next);
   EXPECT_TRUE(prev->merge_next());
   EXPECT_EQ(prev->next(), last);

   // We should have the original buffer.
   EXPECT_EQ(prev, orig_block);
   EXPECT_EQ(prev->outer_size(), orig_size);
 }
	//===-- Unittests for a block of memory -------------------------- C++ --===//
	//
	// 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 <stddef.h>

	#include "src/__support/CPP/array.h"
	#include "src/__support/CPP/bit.h"
	#include "src/__support/CPP/span.h"
	#include "src/__support/block.h"
	#include "src/string/memcpy.h"
	#include "test/UnitTest/Test.h"

	using LIBC_NAMESPACE::Block;
	using LIBC_NAMESPACE::cpp::array;
	using LIBC_NAMESPACE::cpp::bit_ceil;
	using LIBC_NAMESPACE::cpp::byte;
	using LIBC_NAMESPACE::cpp::span;

	TEST(LlvmLibcBlockTest, CanCreateSingleAlignedBlock) {
	constexpr size_t kN = 1024;
	alignas(max_align_t) array<byte, kN> bytes;

	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;

	EXPECT_EQ(reinterpret_cast<uintptr_t>(block) % alignof(Block), size_t{0});
	EXPECT_TRUE(block->is_usable_space_aligned(alignof(max_align_t)));

	Block *last = block->next();
	ASSERT_NE(last, static_cast<Block *>(nullptr));
	EXPECT_EQ(reinterpret_cast<uintptr_t>(last) % alignof(Block), size_t{0});

	EXPECT_EQ(last->outer_size(), sizeof(Block));
	EXPECT_EQ(last->prev_free(), block);
	EXPECT_TRUE(last->used());

	size_t block_outer_size =
	reinterpret_cast<uintptr_t>(last) - reinterpret_cast<uintptr_t>(block);
	EXPECT_EQ(block->outer_size(), block_outer_size);
	EXPECT_EQ(block->inner_size(),
	block_outer_size - sizeof(Block) + Block::PREV_FIELD_SIZE);
	EXPECT_EQ(block->prev_free(), static_cast<Block *>(nullptr));
	EXPECT_FALSE(block->used());
	}

	TEST(LlvmLibcBlockTest, CanCreateUnalignedSingleBlock) {
	constexpr size_t kN = 1024;

	// Force alignment, so we can un-force it below
	alignas(max_align_t) array<byte, kN> bytes;
	span<byte> aligned(bytes);

	auto result = Block::init(aligned.subspan(1));
	EXPECT_TRUE(result.has_value());

	Block block = result;
	EXPECT_EQ(reinterpret_cast<uintptr_t>(block) % alignof(Block), size_t{0});
	EXPECT_TRUE(block->is_usable_space_aligned(alignof(max_align_t)));

	Block *last = block->next();
	ASSERT_NE(last, static_cast<Block *>(nullptr));
	EXPECT_EQ(reinterpret_cast<uintptr_t>(last) % alignof(Block), size_t{0});
	}

	TEST(LlvmLibcBlockTest, CannotCreateTooSmallBlock) {
	array<byte, 2> bytes;
	auto result = Block::init(bytes);
	EXPECT_FALSE(result.has_value());
	}

	TEST(LlvmLibcBlockTest, CanSplitBlock) {
	constexpr size_t kN = 1024;

	// Choose a split position such that the next block's usable space is 512
	// bytes from this one's. This should be sufficient for any machine's
	// alignment.
	const size_t kSplitN = Block::inner_size(512);

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	auto block1 = result;
	size_t orig_size = block1->outer_size();

	result = block1->split(kSplitN);
	ASSERT_TRUE(result.has_value());
	auto block2 = result;

	EXPECT_EQ(block1->inner_size(), kSplitN);
	EXPECT_EQ(block1->outer_size(),
	kSplitN - Block::PREV_FIELD_SIZE + sizeof(Block));

	EXPECT_EQ(block2->outer_size(), orig_size - block1->outer_size());
	EXPECT_FALSE(block2->used());
	EXPECT_EQ(reinterpret_cast<uintptr_t>(block2) % alignof(Block), size_t{0});
	EXPECT_TRUE(block2->is_usable_space_aligned(alignof(max_align_t)));

	EXPECT_EQ(block1->next(), block2);
	EXPECT_EQ(block2->prev_free(), block1);
	}

	TEST(LlvmLibcBlockTest, CanSplitBlockUnaligned) {
	constexpr size_t kN = 1024;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block1 = result;
	size_t orig_size = block1->outer_size();

	constexpr size_t kSplitN = 513;

	result = block1->split(kSplitN);
	ASSERT_TRUE(result.has_value());
	Block block2 = result;

	EXPECT_GE(block1->inner_size(), kSplitN);

	EXPECT_EQ(block2->outer_size(), orig_size - block1->outer_size());
	EXPECT_FALSE(block2->used());
	EXPECT_EQ(reinterpret_cast<uintptr_t>(block2) % alignof(Block), size_t{0});
	EXPECT_TRUE(block2->is_usable_space_aligned(alignof(max_align_t)));

	EXPECT_EQ(block1->next(), block2);
	EXPECT_EQ(block2->prev_free(), block1);
	}

	TEST(LlvmLibcBlockTest, CanSplitMidBlock) {
	// split once, then split the original block again to ensure that the
	// pointers get rewired properly.
	// I.e.
	// [[ BLOCK 1 ]]
	// block1->split()
	// [[ BLOCK1 ]][[ BLOCK2 ]]
	// block1->split()
	// [[ BLOCK1 ]][[ BLOCK3 ]][[ BLOCK2 ]]

	constexpr size_t kN = 1024;
	constexpr size_t kSplit1 = 512;
	constexpr size_t kSplit2 = 256;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block1 = result;

	result = block1->split(kSplit1);
	ASSERT_TRUE(result.has_value());
	Block block2 = result;

	result = block1->split(kSplit2);
	ASSERT_TRUE(result.has_value());
	Block block3 = result;

	EXPECT_EQ(block1->next(), block3);
	EXPECT_EQ(block3->prev_free(), block1);
	EXPECT_EQ(block3->next(), block2);
	EXPECT_EQ(block2->prev_free(), block3);
	}

	TEST(LlvmLibcBlockTest, CannotSplitTooSmallBlock) {
	constexpr size_t kN = 64;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;

	result = block->split(block->inner_size() + 1);
	ASSERT_FALSE(result.has_value());
	}

	TEST(LlvmLibcBlockTest, CannotSplitBlockWithoutHeaderSpace) {
	constexpr size_t kN = 1024;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;

	result = block->split(block->inner_size() - sizeof(Block) + 1);
	ASSERT_FALSE(result.has_value());
	}

	TEST(LlvmLibcBlockTest, CannotMakeBlockLargerInSplit) {
	// Ensure that we can't ask for more space than the block actually has...
	constexpr size_t kN = 1024;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;

	result = block->split(block->inner_size() + 1);
	ASSERT_FALSE(result.has_value());
	}

	TEST(LlvmLibcBlockTest, CanMakeMinimalSizeFirstBlock) {
	// This block does support splitting with minimal payload size.
	constexpr size_t kN = 1024;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;

	result = block->split(0);
	ASSERT_TRUE(result.has_value());
	EXPECT_LE(block->outer_size(), sizeof(Block) + alignof(max_align_t));
	}

	TEST(LlvmLibcBlockTest, CanMakeMinimalSizeSecondBlock) {
	// Likewise, the split block can be minimal-width.
	constexpr size_t kN = 1024;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block1 = result;

	result = block1->split(Block::prev_possible_block_start(
	reinterpret_cast<uintptr_t>(block1->next())) -
	reinterpret_cast<uintptr_t>(block1->usable_space()) +
	Block::PREV_FIELD_SIZE);
	ASSERT_TRUE(result.has_value());
	EXPECT_LE((*result)->outer_size(), sizeof(Block) + alignof(max_align_t));
	}

	TEST(LlvmLibcBlockTest, CanMarkBlockUsed) {
	constexpr size_t kN = 1024;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;
	size_t orig_size = block->outer_size();

	block->mark_used();
	EXPECT_TRUE(block->used());
	EXPECT_EQ(block->outer_size(), orig_size);

	block->mark_free();
	EXPECT_FALSE(block->used());
	}

	TEST(LlvmLibcBlockTest, CannotSplitUsedBlock) {
	constexpr size_t kN = 1024;
	constexpr size_t kSplitN = 512;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;

	block->mark_used();
	result = block->split(kSplitN);
	ASSERT_FALSE(result.has_value());
	}

	TEST(LlvmLibcBlockTest, CanMergeWithNextBlock) {
	// Do the three way merge from "CanSplitMidBlock", and let's
	// merge block 3 and 2
	constexpr size_t kN = 1024;
	constexpr size_t kSplit1 = 512;
	constexpr size_t kSplit2 = 256;
	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block1 = result;
	size_t total_size = block1->outer_size();

	result = block1->split(kSplit1);
	ASSERT_TRUE(result.has_value());

	result = block1->split(kSplit2);
	size_t block1_size = block1->outer_size();
	ASSERT_TRUE(result.has_value());
	Block block3 = result;

	EXPECT_TRUE(block3->merge_next());

	EXPECT_EQ(block1->next(), block3);
	EXPECT_EQ(block3->prev_free(), block1);
	EXPECT_EQ(block1->outer_size(), block1_size);
	EXPECT_EQ(block3->outer_size(), total_size - block1->outer_size());
	}

	TEST(LlvmLibcBlockTest, CannotMergeWithFirstOrLastBlock) {
	constexpr size_t kN = 1024;
	constexpr size_t kSplitN = 512;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block1 = result;

	// Do a split, just to check that the checks on next/prev are different...
	result = block1->split(kSplitN);
	ASSERT_TRUE(result.has_value());
	Block block2 = result;

	EXPECT_FALSE(block2->merge_next());
	}

	TEST(LlvmLibcBlockTest, CannotMergeUsedBlock) {
	constexpr size_t kN = 1024;
	constexpr size_t kSplitN = 512;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;

	// Do a split, just to check that the checks on next/prev are different...
	result = block->split(kSplitN);
	ASSERT_TRUE(result.has_value());

	block->mark_used();
	EXPECT_FALSE(block->merge_next());
	}

	TEST(LlvmLibcBlockTest, CanGetBlockFromUsableSpace) {
	array<byte, 1024> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block1 = result;

	void *ptr = block1->usable_space();
	Block *block2 = Block::from_usable_space(ptr);
	EXPECT_EQ(block1, block2);
	}

	TEST(LlvmLibcBlockTest, CanGetConstBlockFromUsableSpace) {
	constexpr size_t kN = 1024;

	array<byte, kN> bytes{};
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	const Block block1 = result;

	const void *ptr = block1->usable_space();
	const Block *block2 = Block::from_usable_space(ptr);
	EXPECT_EQ(block1, block2);
	}

	TEST(LlvmLibcBlockTest, Allocate) {
	constexpr size_t kN = 1024;

	// Ensure we can allocate everything up to the block size within this block.
	for (size_t i = 0; i < kN; ++i) {
	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;

	if (i > block->inner_size())
	continue;

	auto info = Block::allocate(block, alignof(max_align_t), i);
	EXPECT_NE(info.block, static_cast<Block *>(nullptr));
	}

	// Ensure we can allocate a byte at every guaranteeable alignment.
	for (size_t i = 1; i < kN / alignof(max_align_t); ++i) {
	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;

	size_t alignment = i * alignof(max_align_t);
	if (Block::min_size_for_allocation(alignment, 1) > block->inner_size())
	continue;

	auto info = Block::allocate(block, alignment, 1);
	EXPECT_NE(info.block, static_cast<Block *>(nullptr));
	}
	}

	TEST(LlvmLibcBlockTest, AllocateAlreadyAligned) {
	constexpr size_t kN = 1024;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;
	uintptr_t orig_end = reinterpret_cast<uintptr_t>(block) + block->outer_size();

	constexpr size_t SIZE = Block::PREV_FIELD_SIZE + 1;

	auto [aligned_block, prev, next] =
	Block::allocate(block, alignof(max_align_t), SIZE);

	// Since this is already aligned, there should be no previous block.
	EXPECT_EQ(prev, static_cast<Block *>(nullptr));

	// Ensure we the block is aligned and large enough.
	EXPECT_NE(aligned_block, static_cast<Block *>(nullptr));
	EXPECT_TRUE(aligned_block->is_usable_space_aligned(alignof(max_align_t)));
	EXPECT_GE(aligned_block->inner_size(), SIZE);

	// Check the next block.
	EXPECT_NE(next, static_cast<Block *>(nullptr));
	EXPECT_EQ(aligned_block->next(), next);
	EXPECT_EQ(reinterpret_cast<uintptr_t>(next) + next->outer_size(), orig_end);
	}

	TEST(LlvmLibcBlockTest, AllocateNeedsAlignment) {
	constexpr size_t kN = 1024;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;

	uintptr_t orig_end = reinterpret_cast<uintptr_t>(block) + block->outer_size();

	// Now pick an alignment such that the usable space is not already aligned to
	// it. We want to explicitly test that the block will split into one before
	// it.
	size_t alignment = alignof(max_align_t);
	while (block->is_usable_space_aligned(alignment))
	alignment += alignof(max_align_t);

	auto [aligned_block, prev, next] = Block::allocate(block, alignment, 10);

	// Check the previous block was created appropriately. Since this block is the
	// first block, a new one should be made before this.
	EXPECT_NE(prev, static_cast<Block *>(nullptr));
	EXPECT_EQ(aligned_block->prev_free(), prev);
	EXPECT_EQ(prev->next(), aligned_block);
	EXPECT_EQ(prev->outer_size(), reinterpret_cast<uintptr_t>(aligned_block) -
	reinterpret_cast<uintptr_t>(prev));

	// Ensure we the block is aligned and the size we expect.
	EXPECT_NE(next, static_cast<Block *>(nullptr));
	EXPECT_TRUE(aligned_block->is_usable_space_aligned(alignment));

	// Check the next block.
	EXPECT_NE(next, static_cast<Block *>(nullptr));
	EXPECT_EQ(aligned_block->next(), next);
	EXPECT_EQ(reinterpret_cast<uintptr_t>(next) + next->outer_size(), orig_end);
	}

	TEST(LlvmLibcBlockTest, PreviousBlockMergedIfNotFirst) {
	constexpr size_t kN = 1024;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;

	// Split the block roughly halfway and work on the second half.
	auto result2 = block->split(kN / 2);
	ASSERT_TRUE(result2.has_value());
	Block newblock = result2;
	ASSERT_EQ(newblock->prev_free(), block);
	size_t old_prev_size = block->outer_size();

	// Now pick an alignment such that the usable space is not already aligned to
	// it. We want to explicitly test that the block will split into one before
	// it.
	size_t alignment = alignof(max_align_t);
	while (newblock->is_usable_space_aligned(alignment))
	alignment += alignof(max_align_t);

	// Ensure we can allocate in the new block.
	auto [aligned_block, prev, next] = Block::allocate(newblock, alignment, 1);

	// Now there should be no new previous block. Instead, the padding we did
	// create should be merged into the original previous block.
	EXPECT_EQ(prev, static_cast<Block *>(nullptr));
	EXPECT_EQ(aligned_block->prev_free(), block);
	EXPECT_EQ(block->next(), aligned_block);
	EXPECT_GT(block->outer_size(), old_prev_size);
	}

	TEST(LlvmLibcBlockTest, CanRemergeBlockAllocations) {
	// Finally to ensure we made the split blocks correctly via allocate. We
	// should be able to reconstruct the original block from the blocklets.
	//
	// This is the same setup as with the `AllocateNeedsAlignment` test case.
	constexpr size_t kN = 1024;

	array<byte, kN> bytes;
	auto result = Block::init(bytes);
	ASSERT_TRUE(result.has_value());
	Block block = result;

	Block *orig_block = block;
	size_t orig_size = orig_block->outer_size();

	Block *last = block->next();

	ASSERT_EQ(block->prev_free(), static_cast<Block *>(nullptr));

	// Now pick an alignment such that the usable space is not already aligned to
	// it. We want to explicitly test that the block will split into one before
	// it.
	size_t alignment = alignof(max_align_t);
	while (block->is_usable_space_aligned(alignment))
	alignment += alignof(max_align_t);

	auto [aligned_block, prev, next] = Block::allocate(block, alignment, 1);

	// Check we have the appropriate blocks.
	ASSERT_NE(prev, static_cast<Block *>(nullptr));
	ASSERT_EQ(aligned_block->prev_free(), prev);
	EXPECT_NE(next, static_cast<Block *>(nullptr));
	EXPECT_EQ(aligned_block->next(), next);
	EXPECT_EQ(next->next(), last);

	// Now check for successful merges.
	EXPECT_TRUE(prev->merge_next());
	EXPECT_EQ(prev->next(), next);
	EXPECT_TRUE(prev->merge_next());
	EXPECT_EQ(prev->next(), last);

	// We should have the original buffer.
	EXPECT_EQ(prev, orig_block);
	EXPECT_EQ(prev->outer_size(), orig_size);
	}