validation: reduce block index comparison overhead #33637

pull l0rinc wants to merge 7 commits into bitcoin:master from l0rinc:l0rinc/block_index_comparators changing 12 files +270 −43
  1. l0rinc commented at 1:54 AM on October 16, 2025: contributor

    Problem: Block-index ordering is used by chain selection and CheckBlockIndex(). The work comparator makes repeated out-of-line comparisons of chain work, sequence IDs, and addresses. CheckBlockIndex() is enabled by default on regtest, including functional tests, but disabled by default on mainnet.

    Fix: Inline the block-index comparators, compare the work-ordering key with std::tie, and use one three-way comparison per 32-bit word in arith_uint256. Ordering is unchanged. Fixed-order unit tests pin the expected results, and two differential fuzz targets compare against the original implementations.

    Measurement: Earlier GCC 15.0.1 and Clang 22.0.0 runs reported the following base-to-final improvements on the older stack. These are historical measurements, not fresh measurements of the current head.

    Compiler Synthetic 256-bit work comparisons CheckBlockIndex
    GCC 15.0.1 6.51× 1.62×
    Clang 22.0.0 6.80× 1.39×

    The current benchmark also covers 12-bit and 96-bit work values.

    <details> <summary>Measure the current comparison workloads</summary>

    cmake -B build -DBUILD_BENCH=ON -DCMAKE_BUILD_TYPE=Release &&
cmake --build build -j10 --target bench_bitcoin &&
build/bin/bench_bitcoin -filter='CBlockIndexWorkComparator.*|CheckBlockIndex' -min-time=5000

    Compare before and after builds with the same compiler and configuration. The quoted historical runs used benchmark commit b60450fae8 and final commit deb58eea2f.

    </details>

  2. DrahtBot added the label Refactoring on Oct 16, 2025
  3. DrahtBot commented at 1:54 AM on October 16, 2025: contributor

    <!--e57a25ab6845829454e8d69fc972939a-->

    The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

    <!--006a51241073e994b41acfe9ec718e94-->

    Code Coverage & Benchmarks

    For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33637.

    <!--021abf342d371248e50ceaed478a90ca-->

    Reviews

    See the guideline and AI policy for information on the review process.

    Type Reviewers
    Concept ACK mzumsande
    Approach ACK Raimo33
    Stale ACK laanwj, optout21

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    Conflicts

    Reviewers, this pull request conflicts with the following ones:

    • #33324 <sub><img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/33324.svg"></sub> (blocks: add resumable reobfuscation for existing block files by l0rinc)

    If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

    <!--5faf32d7da4f0f540f40219e4f7537a3-->

  4. Raimo33 commented at 9:16 AM on October 17, 2025: contributor

    Approach ACK

    I have tested the new block index comparator but I’ll refrain from acking the added benchmarks/tests

  5. in src/bench/blockstorage.cpp:40 in dc7e70e9ac outdated 
      35 | +
  36 | +        blocks.push_back(std::move(block));
  37 | +    }
  38 | +    std::ranges::shuffle(blocks, rng);
  39 | +
  40 | +    bench.run([&] {
    sipa commented at 3:00 PM on October 17, 2025:

    Mind using bench.batch(n * n).units("cmp") or so here, to put the output units in perspective?

    l0rinc commented at 5:55 AM on October 18, 2025:

    Done, updated the commit messages and PR descriptions as well.

  6. l0rinc force-pushed on Oct 18, 2025
  7. l0rinc renamed this:
    refactor: optimize block index comparisons (1.4-7.7x faster)
    refactor: optimize block index comparisons (1.4-6.8x faster)
    on Oct 18, 2025
  8. Christewart commented at 9:34 PM on October 18, 2025: contributor

    I attempted to run the script, not really sure what these results indicate. Just pasting what the results were

    <details>

    Darwin Chriss-MacBook-Pro.local 24.6.0 Darwin Kernel Version 24.6.0: Mon Jul 14 11:30:55 PDT 2025; root:xnu-11417.140.69~1/RELEASE_ARM64_T6031 arm64

    Apple clang version 17.0.0 (clang-1700.3.19.1)
Target: arm64-apple-darwin24.6.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

    |              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                4.97 |      201,237,014.91 |    0.4% |      5.49 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           43,777.21 |           22,842.94 |    0.3% |      5.41 | `CheckBlockIndex`

    |              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                1.89 |      529,694,702.31 |    0.1% |      5.50 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           38,303.87 |           26,107.02 |    0.1% |      5.35 | `CheckBlockIndex`

    |              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.31 |      432,334,219.11 |    0.6% |      5.45 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           33,598.60 |           29,763.15 |    0.2% |      5.32 | `CheckBlockIndex`

    |              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                0.78 |    1,287,258,159.19 |    0.1% |      5.46 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           31,055.32 |           32,200.61 |    0.1% |      5.30 | `CheckBlockIndex`

    </details

  9. l0rinc commented at 12:24 AM on October 19, 2025: contributor

    Thanks for the measurements @Christewart, this is how your measurements compare to mine (but most importantly how it compares to master): <img width="2385" height="883" alt="image" src="https://github.com/user-attachments/assets/96a59d25-292e-4e11-bd2c-3fb11a5b13cb" />

  10. laanwj approved
  11. laanwj commented at 8:44 AM on October 22, 2025: member

    Code review ACK c15d839aefba017e64f14cd9cd2779655352f4b6 i did not run the benchmarks but the code changes look good, using <=> makes sense.

  12. DrahtBot added the label Needs rebase on Oct 27, 2025
  13. l0rinc force-pushed on Oct 28, 2025
  14. l0rinc commented at 11:19 PM on October 28, 2025: contributor

    Rebased after #29640 - only change was adjusting the comment

  15. DrahtBot removed the label Needs rebase on Oct 28, 2025
  16. in src/test/blockchain_tests.cpp:127 in 08d098947a outdated 
     122 | +    auto old_comparator{[](const CBlockIndex* pa, const CBlockIndex* pb) -> bool {
 123 | +        // First sort by most total work, ...
 124 | +        if (pa->nChainWork > pb->nChainWork) return false;
 125 | +        if (pa->nChainWork < pb->nChainWork) return true;
 126 | +
 127 | +        // ... then by earliest time received, ...
    mzumsande commented at 8:41 PM on October 30, 2025:

    should take the latest comments from the old function after #29640

    l0rinc commented at 8:37 AM on October 31, 2025:

    ~I have already done that, which parts do you think I'm missing?~ Edit: ah in the tests, good point, let me update it

  17. in src/test/arith_uint256_tests.cpp:281 in 08d098947a outdated 
     274 | @@ -275,8 +275,43 @@ BOOST_AUTO_TEST_CASE( comparison ) // <= >= < >
 275 |          BOOST_CHECK(! (TmpL < R1L)); BOOST_CHECK(! (R1L > TmpL));
 276 |      }
 277 |  
 278 | -    BOOST_CHECK_LT(ZeroL,
 279 | -                   OneL);
 280 | +    BOOST_CHECK_LT(ZeroL, OneL);
 281 | +}
 282 | +
 283 | +BOOST_AUTO_TEST_CASE(comparison_equivalence)
    mzumsande commented at 9:13 PM on October 30, 2025:

    commit msg 08d098947aaeae67e3aeef262df1ecdbdbed744a: wway ->way

    l0rinc commented at 10:57 AM on October 31, 2025:

    done

  18. in src/test/blockchain_tests.cpp:120 in 08d098947a outdated 
     116 | @@ -117,6 +117,43 @@ BOOST_AUTO_TEST_CASE(num_chain_tx_max)
 117 |      BOOST_CHECK_EQUAL(block_index.m_chain_tx_count, std::numeric_limits<uint64_t>::max());
 118 |  }
 119 |  
 120 | +BOOST_AUTO_TEST_CASE(cblockindex_comparator_equivalence)
    mzumsande commented at 9:15 PM on October 30, 2025:

    this looks like a fuzz test, why not make it an actual fuzz target out of this?

    mzumsande commented at 9:18 PM on October 30, 2025:

    would suggest to add a bit more explanation, e.g. mentioning that old_comparator is a snapshot of an old implementation, so that people who look at this in years understand where it's coming from.

    l0rinc commented at 10:56 AM on October 31, 2025:

    I strongly dislike code comments, I prefer explaining with live code over dead comments - and if people disagree they can always do a blame which instantly reveals the purpose since I also over-explain in commit messages usually. Are the names old_comparator in a cblockindex_comparator_equivalence not enough to make it obvious that? I I have added a comment anyway, let me know if it helps.

    l0rinc commented at 10:56 AM on October 31, 2025:

    I look at fuzz tests as exploratory tools that are hard to write and run and debug and do code coverage on - not trivial to maintain (see #33731), it's definitely not my go-to way to test something. This is just a randomized property based unit test - easy to debug, easy to run and understand. But looking at the tests again, I can make it more deterministic so that it hits all important branches which allows me to reduce the iteration count - code coverage and debugging shows this regularly tests each branch now (green line on left side): <img width="616" height="520" alt="image" src="https://github.com/user-attachments/assets/3afe6e0a-779e-4ecb-bd8c-1f4c3b8f1345" /> Added you as coauthor.

    dergoegge commented at 12:43 PM on November 6, 2025:

    I look at fuzz tests as exploratory tools that are hard to write and run and debug and do code coverage ... not trivial to maintain ... not my go-to way to test something

    There is a learning curve to writing and using fuzz testing but it is 100% worth getting in to. The maintenance aspect only relates to running them using libFuzzer on macOS.

    On average, coverage guided fuzzing will be magnitudes better at finding bugs than this style of unit test. For something as small as the comparator your approach is probably good enough, although you could just have a fixed list of test cases that enumerate all possibilities (for the old comparator) instead? (maybe you do already, didn't look)

  19. in src/node/blockstorage.h:90 in a5584716cb 
      86 | @@ -87,12 +87,20 @@ static constexpr uint32_t UNDO_DATA_DISK_OVERHEAD{STORAGE_HEADER_BYTES + uint256
  87 |  using BlockMap = std::unordered_map<uint256, CBlockIndex, BlockHasher>;
  88 |  
  89 |  struct CBlockIndexWorkComparator {
  90 | -    bool operator()(const CBlockIndex* pa, const CBlockIndex* pb) const;
  91 | +    // First sort by most total work (descending), then by earliest activatable time (ascending), then by pointer value (ascending).
    mzumsande commented at 9:48 PM on October 30, 2025:

    I find "ascending/descending" confusing here, I would have expected the opposites: "descending work" means most work first, but the strict weak ordering of C++ comparators would place the one with the lower work first.

    Would suggest something like "First compare by work (less first), then by earliest activatable time (higher sequence first), then by pointer value (higher first)."

    l0rinc commented at 10:56 AM on October 31, 2025:

    I wanted to use the SQL order-by terminology here

    Ascending order puts smaller values first, where “smaller” is defined in terms of the < operator. Similarly, descending order is determined with the > operator.

    But you're right, I inverted the terminology, added a dedicated test to check for hard-coded order (first param is increasing, second is decreasing), updated the comments (this is why I find comments a lazy solution, it's too easy to keep them up-to-date), added you as coauthor.

  20. mzumsande commented at 10:08 PM on October 30, 2025: contributor

    Concept ACK

    Not 100% sure yet about 2dd0f2ced35a268bcab661c671e7c70271cdd91f, seems like inlining gives most of the speedup, whereas the gain of using the spaceship operator (which comes at the cost of readability) is marginal.

  21. l0rinc force-pushed on Oct 31, 2025
  22. l0rinc force-pushed on Oct 31, 2025
  23. l0rinc commented at 1:13 PM on October 31, 2025: contributor

    Pushed, thanks for the review, you had a few good points, added you as coauthor.

    the gain of using the spaceship operator (which comes at the cost of readability) is marginal.

    the spaceship might not be very familiar to us yet, but it's arguably simpler, having fewer moving parts, and some compilers prefer that over the manual comparisons.

  24. in src/test/arith_uint256_tests.cpp:286 in 2d03d94535 outdated 
     283 | +BOOST_AUTO_TEST_CASE(comparison_equivalence)
 284 | +{
 285 | +    struct TestableArithUint256 : arith_uint256 {
 286 | +        static int compare_original(const TestableArithUint256& a, const TestableArithUint256& b) {
 287 | +            constexpr int WIDTH = 8; // 256 / 32
 288 | +            for (int i = WIDTH - 1; i >= 0; i--) {
    optout21 commented at 12:31 PM on November 3, 2025:

    nit: --i is preferred

    l0rinc commented at 12:43 PM on November 3, 2025:

    Generally yes, but here I wanted to copy the original code as closely as possible

    l0rinc commented at 12:48 PM on November 3, 2025:

    Pushed anyway, thanks

  25. in src/test/blockchain_tests.cpp:137 in 2d03d94535 outdated 
     132 | +
 133 | +        // ... then by earliest activatable time, ...
 134 | +        if (pa->nSequenceId < pb->nSequenceId)
 135 | +            return false;
 136 | +        if (pa->nSequenceId > pb->nSequenceId)
 137 | +                return true;
    optout21 commented at 12:35 PM on November 3, 2025:

    nit: indentation seems off (extra indent)

    l0rinc commented at 12:48 PM on November 3, 2025:

    done, thanks

  26. optout21 commented at 12:44 PM on November 3, 2025: contributor

    utACK 5cbb9a40873203ea5a4dd0aa7127c9756da2f607

    An evident, localized micro-optimization in a hot-path. I haven't run measurements.

  27. DrahtBot requested review from laanwj on Nov 3, 2025
  28. DrahtBot requested review from mzumsande on Nov 3, 2025
  29. l0rinc force-pushed on Nov 3, 2025
  30. optout21 commented at 12:52 PM on November 3, 2025: contributor

    reACK 80bfeaa240611401c1ffa41f6968b1f79b621938 Rebase.

    Prev: reACK 78b43065a1746c19f74fe6380d765d5922e5c541 Rebase, no content changes. reACK 6e9061f8b7ad77df4566990121f5bebc1f9e6e15 utACK 237eec0f7ca095bc60e40ee94ba1a160a7064753 Re-acked (after 7 mins :D ), only minor/formatting changes since last review

  31. maflcko commented at 3:34 PM on November 6, 2025: member

    Profiling the performance regression in #33618 (comment) revealed that CBlockIndexWorkComparator and its underlying base_uint<256u>::CompareTo are hot paths during block validation, consuming ~4% of CPU time.

    I don't follow here. The issue is about the additional CWallet::WriteBestBlock overhead? CBlockIndexWorkComparator seems unrelated to the issue, at least I can't see how it changed the result between 29.x and 30.x.

    Instead of mentioning an unrelated issue, I think it could be better to mention what real-world effect this improvement has. I think that is -checkblockindex (default in regtest) and possibly LoadExternalBlockFile/LoadBlockIndex?

  32. l0rinc commented at 4:22 PM on November 6, 2025: contributor

    CBlockIndexWorkComparator seems unrelated to the issue

    The original issue won't be fixed since it's not exactly a bug, but we could still speed up the regression by optimizing another bottleneck. Since you found the etymology confusing, I have removed the details from the description, only mentioned #33618 (comment) for the flame graph that show this being one of the bottlenecks. Not the biggest one, but the one we can easily optimize and clean up.

    I think that is -checkblockindex (default in regtest)

    Yes, this was mentioned in the benchmarking section.

    possibly LoadExternalBlockFile/LoadBlockIndex

    Yes, it's used explicitly in Chainstate in FindMostWorkChain, PruneBlockIndexCandidates, ActivateBestChain and InvalidateBlock. And ChainstateManager in LoadBlockIndex, CheckBlockIndex, ActivateSnapshot and PopulateAndValidateSnapshot. But the setBlockIndexCandidates usages should already suffice as motivation, I'd say:

    git grep 'setBlockIndexCandidates.' src/validation.cpp | wc -l 
   44
  33. in src/node/blockstorage.h:94 in 237eec0f7c outdated 
      86 | @@ -87,12 +87,21 @@ static constexpr uint32_t UNDO_DATA_DISK_OVERHEAD{STORAGE_HEADER_BYTES + uint256
  87 |  using BlockMap = std::unordered_map<uint256, CBlockIndex, BlockHasher>;
  88 |  
  89 |  struct CBlockIndexWorkComparator {
  90 | -    bool operator()(const CBlockIndex* pa, const CBlockIndex* pb) const;
  91 | +    // First sort by most total work (ascending), then by earliest activatable time (descending), then by pointer value (descending).
  92 | +    // Pointer tiebreak should only happen with blocks loaded from disk, as those share the same id: 0 for blocks on the best chain, 1 for all others.
  93 | +    bool operator()(const CBlockIndex* pa, const CBlockIndex* pb) const noexcept
  94 | +    {
  95 | +        return std::tie(pa->nChainWork, pb->nSequenceId, pb)
    l0rinc commented at 10:50 PM on November 12, 2025:

    I thought of eliminating the worst case here (when pa == pb, where it has to do the comparison for every byte) with something like:

    return pa != pb &&
       std::tie(pa->nChainWork, pb->nSequenceId, pb)
     < std::tie(pb->nChainWork, pa->nSequenceId, pa);

    But the benchmarks indicate that it's not really faster.

    <details><summary>benchmark with pointer duplicates</summary>

    // Copyright (c) 2025-present The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include <arith_uint256.h>
#include <bench/bench.h>
#include <chain.h>
#include <node/blockstorage.h>
#include <random.h>
#include <uint256.h>

#include <algorithm>
#include <memory>
#include <vector>

static void CBlockIndexWorkComparator(benchmark::Bench& bench)
{
    FastRandomContext rng{/*fDeterministic=*/true};

    constexpr size_t n{1'000};
    std::vector<std::shared_ptr<CBlockIndex>> blocks;
    blocks.reserve(n);
    for (size_t i{0}; i < n; ++i) {
        auto block{std::make_shared<CBlockIndex>()};
        block->nChainWork = UintToArith256(rng.rand256());
        block->nSequenceId = int32_t(rng.rand32());
        if (i % 10 == 1) {
            // Have some duplicates
            if (rng.randbool()) {
                block = blocks.back();
            } else {
                if (rng.randbool()) block->nChainWork = blocks.back()->nChainWork;
                if (rng.randbool()) block->nSequenceId = blocks.back()->nSequenceId;
            }
        }
        blocks.push_back(std::move(block));
    }
    std::ranges::shuffle(blocks, rng);

    const node::CBlockIndexWorkComparator comparator;
    bench.batch(n * n).unit("cmp").run([&] {
        for (size_t i{0}; i < n; ++i) {
            const auto* lhs{blocks[i].get()};
            for (size_t j{0}; j < n; ++j) {
                const auto* rhs{blocks[j].get()};
                const bool result{comparator(lhs, rhs)};
                ankerl::nanobench::doNotOptimizeAway(result);
            }
        }
    });
}

BENCHMARK(CBlockIndexWorkComparator, benchmark::PriorityLevel::HIGH);

    </details>

    b17504b611 refactor: optimize CBlockIndexWorkComparator with std::tie

    ns/cmp cmp/s err% ins/cmp cyc/cmp IPC bra/cmp miss% total benchmark
    2.13 469,485,340.38 0.2% 15.07 5.09 2.959 4.02 0.1% 11.01 CBlockIndexWorkComparator
    ns/op op/s err% ins/op cyc/op IPC bra/op miss% total benchmark
    90,265.10 11,078.48 0.1% 637,536.00 215,946.18 2.952 178,844.00 0.0% 10.84 CheckBlockIndex

    2b77e567d8 refactor: short-circuit CBlockIndex comparator for equality

    ns/cmp cmp/s err% ins/cmp cyc/cmp IPC bra/cmp miss% total benchmark
    2.60 385,002,212.20 0.0% 18.00 6.22 2.894 5.00 0.0% 11.00 CBlockIndexWorkComparator
    ns/op op/s err% ins/op cyc/op IPC bra/op miss% total benchmark
    94,110.53 10,625.80 0.0% 682,454.03 225,242.05 3.030 186,486.01 0.0% 11.00 CheckBlockIndex
  34. DrahtBot added the label Needs rebase on Nov 25, 2025
  35. l0rinc force-pushed on Nov 25, 2025
  37. DrahtBot removed the label Needs rebase on Nov 25, 2025
  38. l0rinc referenced this in commit d42c922e92 on Nov 26, 2025
  39. l0rinc commented at 5:13 PM on January 15, 2026: contributor

    Rebased to fix silent merge conflict.

  40. l0rinc force-pushed on Jan 15, 2026
  41. DrahtBot added the label CI failed on Jan 15, 2026
  42. DrahtBot commented at 7:13 PM on January 15, 2026: contributor

    <!--85328a0da195eb286784d51f73fa0af9-->

    🚧 At least one of the CI tasks failed. <sub>Task iwyu: https://github.com/bitcoin/bitcoin/actions/runs/21039886920/job/60501264056</sub> <sub>LLM reason (✨ experimental): IWYU reported a failure after adjusting includes in src/node/blockstorage.h, causing the CI to fail.</sub>

    <details><summary>Hints</summary>

    Try to run the tests locally, according to the documentation. However, a CI failure may still happen due to a number of reasons, for example:

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    • An intermittent issue.

    Leave a comment here, if you need help tracking down a confusing failure.

    </details>

  43. l0rinc force-pushed on Jan 15, 2026
  44. DrahtBot removed the label CI failed on Jan 15, 2026
  45. DrahtBot added the label Needs rebase on Feb 2, 2026
  46. l0rinc commented at 10:44 AM on February 2, 2026: contributor

    Rebased after conflict with https://github.com/bitcoin/bitcoin/pull/34179/changes#diff-ed3f90693a242b38b9719af171de8f55183576957676dfa358945bea22276bd5R139, ready for review again.

  47. l0rinc force-pushed on Feb 2, 2026
  48. DrahtBot removed the label Needs rebase on Feb 2, 2026
  49. sipa commented at 5:16 PM on February 2, 2026: member

    You should really add a fuzz test here to compare old and new behavior as suggested before; it's the perfect use case for it, as it avoids the need for putting presumed knowledge about potential bugs in the unit tests you create.

  50. l0rinc force-pushed on Feb 2, 2026
  51. l0rinc commented at 9:46 PM on February 2, 2026: contributor

    You should really add a fuzz test here to compare old and new behavior

    Thanks for the hint, I've split the differential fuzzer and kept the simple unit tests o lock in the expected ordering of both comparators. After a while (if fuzzers can't find any difference) we should be able to remove the fuzzers while keeping only the unit tests.

  52. maflcko commented at 7:07 AM on February 3, 2026: member

    As pointed out earlier, most of the speedup comes from a move-only inline (https://github.com/bitcoin/bitcoin/pull/33637#pullrequestreview-3401558839)?

    I think it would be better to just submit a trivial to review move-only change stand-alone, which wouldn't need in-depth review and dedicated differential unit/fuzz tests. Or at least the move-only change should be the first change. This way, it is easier to see if the other changes are worth it to review/test at all.

  53. l0rinc commented at 11:44 AM on February 3, 2026: contributor

    As pointed out earlier, most of the speedup comes from a move-only inline

    That's actually what enables the other ones to shine, but I don't mind reordering the commits to make it obvious. The biggest optimization is the spaceship (with inline), it's now the last commit.

    <img width="1499" height="869" alt="image" src="https://github.com/user-attachments/assets/fd838e94-9523-40f0-92e3-1a9774d17056" />

    <details> <summary>Measurements</summary>

    for commit in 8b54cc2e71b015b651d7dcbfc3033c1f76c37e4e 9304b3b225f4dcc06b007d073035a586e1806951 0473240b4f8d29016778ebd73745c610c2b437e8 d64d9432a06879e57702f8188a764eb3fc8f2751 c2f69e78ba69ee4232c5190a41509e142b039e8b 7cb0c5f1fc70d57277689d114ab2da14af2a0696 df0153a846036f94e51ab70b7c91491b138d3569; do \
    git fetch origin $commit >/dev/null 2>&1 && git checkout $commit >/dev/null 2>&1 && echo "" && git log -1 --pretty='%h %s' && \
    rm -rfd build >/dev/null 2>&1 && cmake -B build -DBUILD_BENCH=ON -DCMAKE_BUILD_TYPE=Release >/dev/null 2>&1 && \
    cmake --build build -j$(nproc) >/dev/null 2>&1 && \
    for _ in $(seq 3); do \
      sleep 5; \
      sudo taskpolicy -t 5 -l 5 nice -n -20 ./build/bin/bench_bitcoin -filter='CBlockIndexWorkComparator|CheckBlockIndex' -min-time=1000; \
    done; \
done


8b54cc2e71 bench: add benchmark to measure `CBlockIndexWorkComparator` performance

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                4.41 |      226,584,742.96 |    0.8% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           38,253.37 |           26,141.49 |    0.9% |      1.09 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                4.35 |      229,642,637.11 |    0.2% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           38,213.19 |           26,168.97 |    0.5% |      1.10 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                4.37 |      228,881,057.73 |    0.3% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           38,287.78 |           26,117.99 |    0.4% |      1.10 | `CheckBlockIndex`

9304b3b225 test: add sorting tests for `CBlockIndexWorkComparator` and `arith_uint256`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                4.39 |      227,961,262.13 |    0.5% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           38,333.93 |           26,086.55 |    0.2% |      1.10 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                4.39 |      227,728,690.97 |    0.7% |      1.11 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           39,671.02 |           25,207.32 |    0.3% |      1.10 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                4.40 |      227,294,352.21 |    0.5% |      1.09 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           38,971.06 |           25,660.07 |    1.1% |      1.10 | `CheckBlockIndex`

0473240b4f move-only: inline `CBlockIndex` comparators to header

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.88 |      347,302,616.35 |    0.3% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           36,701.33 |           27,246.97 |    0.3% |      1.10 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.87 |      348,283,873.30 |    0.2% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           36,790.73 |           27,180.76 |    0.6% |      1.10 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.87 |      348,095,671.92 |    0.2% |      1.09 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           36,534.37 |           27,371.49 |    0.3% |      1.10 | `CheckBlockIndex`

d64d9432a0 test/fuzz: add equivalence coverage for comparison refactors

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.88 |      347,680,941.08 |    0.5% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           37,044.83 |           26,994.32 |    1.1% |      1.08 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.90 |      345,339,421.65 |    0.6% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           37,174.31 |           26,900.30 |    1.4% |      1.09 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.88 |      346,925,394.89 |    0.3% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           37,287.05 |           26,818.96 |    1.6% |      1.09 | `CheckBlockIndex`

c2f69e78ba refactor: optimize `CBlockIndexWorkComparator` with `std::tie`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.00 |      499,008,850.73 |    0.2% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           33,476.29 |           29,871.88 |    1.0% |      1.10 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.03 |      493,360,414.53 |    0.5% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           33,342.34 |           29,991.90 |    0.6% |      1.10 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.01 |      498,514,389.19 |    0.5% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           32,297.54 |           30,962.11 |    0.9% |      1.10 | `CheckBlockIndex`

7cb0c5f1fc refactor: inline `arith_uint256` comparison operator

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.18 |      459,159,880.91 |    0.2% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           32,006.20 |           31,243.95 |    0.7% |      1.10 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.18 |      458,414,231.91 |    0.3% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           31,780.27 |           31,466.07 |    0.5% |      1.10 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                2.19 |      457,429,572.18 |    0.2% |      1.10 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           32,536.14 |           30,735.06 |    1.2% |      1.09 | `CheckBlockIndex`

df0153a846 refactor: optimize `arith_uint256` comparison with spaceship operator

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                0.68 |    1,473,011,136.06 |    0.5% |      1.06 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           27,528.11 |           36,326.51 |    0.2% |      1.10 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                0.69 |    1,451,170,702.42 |    1.0% |      1.07 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           27,875.27 |           35,874.09 |    0.4% |      1.10 | `CheckBlockIndex`

|              ns/cmp |               cmp/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                0.68 |    1,477,110,677.23 |    0.2% |      1.06 | `CBlockIndexWorkComparator`

|               ns/op |                op/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|           29,059.25 |           34,412.45 |    0.7% |      1.12 | `CheckBlockIndex`

    </details>

    Besides moving the inlines earlier, I also added noexcept to operator<=>(const base_uint and split the general unit test (which we should have regardless of the upcoming changes, they set the baseline to document current behavior) and the fuzz tests which probe and compare against the old code. Added the best measurements of 3 from above to the non-test commit messages for reference.

  54. l0rinc force-pushed on Feb 3, 2026
  55. sedited requested review from optout21 on Jul 24, 2026
  56. DrahtBot added the label Needs rebase on Aug 21, 2026
  57. optout21 commented at 1:02 PM on August 21, 2026: contributor

    reACK 703165e6d3b9fbd58b9c31ddce0e961047fc5e71 No significant new changes, no remarks. P.S.: I'm aware this PR needs a rebase currently.

  58. l0rinc force-pushed on Aug 21, 2026
  59. DrahtBot added the label CI failed on Aug 21, 2026
  60. DrahtBot commented at 9:19 PM on August 21, 2026: contributor

    <!--85328a0da195eb286784d51f73fa0af9-->

    🚧 At least one of the CI tasks failed. <sub>Task test ancestor commits: https://github.com/bitcoin/bitcoin/actions/runs/32521038313/job/96893054160</sub> <sub>LLM reason (✨ experimental): CI failed due to a C++ build compile error in arith_uint256_tests.cpp (“base specifier must name a class”) from BOOST_AUTO_TEST_CASE/fixture macro expansion.</sub>

    <details><summary>Hints</summary>

    Try to run the tests locally, according to the documentation. However, a CI failure may still happen due to a number of reasons, for example:

    • Possibly due to a silent merge conflict (the changes in this pull request being incompatible with the current code in the target branch). If so, make sure to rebase on the latest commit of the target branch.

    • A sanitizer issue, which can only be found by compiling with the sanitizer and running the affected test.

    • An intermittent issue.

    Leave a comment here, if you need help tracking down a confusing failure.

    </details>

  61. l0rinc force-pushed on Aug 21, 2026
  62. DrahtBot removed the label Needs rebase on Aug 21, 2026
  63. l0rinc force-pushed on Aug 21, 2026
  64. DrahtBot removed the label CI failed on Aug 22, 2026
  65. optout21 commented at 3:54 AM on August 22, 2026: contributor

    reACK 0d1119129fd2f9e7700702766121294b6fdf9d27 Rebased; no relevant changes, no remarks.

  66. bench: add block index work comparisons
    Measure comparisons with 12-, 96- and 256-bit synthetic chainwork.
The bounded cases exercise equal high words instead of having almost every comparison decided by the highest word.
    24e5dc377b
  67. test: pin block work and arith_uint256 sort order
    Cover numeric work ordering, sequence IDs including a precious-block ID, and the pointer tie-break for equal work and sequence IDs.
    a8d1e89ae6
  68. refactor: inline block index comparators
    Move both comparator bodies into the header unchanged so callers can inline them.
    ed48f5cdbd
  69. fuzz: add comparator equivalence targets
    Compare arithmetic ordering and block-index ordering against snapshots of their original implementations, including equal values and pointer ties.

Co-authored-by: Martin Zumsande <mzumsande@gmail.com>
    57998bb4d4
  70. l0rinc force-pushed on Oct 1, 2026
  71. refactor: compare block work keys with std::tie
    Express the existing work, sequence ID and pointer ordering as a tuple comparison.
Cross the sequence IDs and pointers to preserve their descending order, while work remains ascending.

Co-authored-by: Martin Zumsande <mzumsande@gmail.com>
    49195a396e
  72. refactor: inline arith_uint256 comparison
    Keep the high-to-low word comparison in `operator<=>` and return its ordering directly.
This makes the subsequent per-word comparison change visible without a separate `CompareTo()` call.
    ed7bb75a2d
  73. refactor: use per-word arith_uint256 comparison
    Compare each pair of 32-bit words once with `<=>`, returning the first unequal ordering.
The high-to-low traversal and equal-value result remain unchanged.
    62ddd1197c
  74. l0rinc force-pushed on Oct 1, 2026
  75. DrahtBot added the label CI failed on Oct 1, 2026
  76. DrahtBot commented at 6:39 AM on October 1, 2026: contributor

    <!--85328a0da195eb286784d51f73fa0af9-->

    🚧 At least one of the CI tasks failed. <sub>Task iwyu: https://github.com/bitcoin/bitcoin/actions/runs/36824900456/job/110248294741</sub> <sub>LLM reason (✨ experimental): CI failed because the IWYU (include-what-you-use) check reported a missing/incorrect #include and forced the job to fail (Failure generated from IWYU).</sub>

    <details><summary>Hints</summary>

    Try to run the tests locally, according to the documentation. However, a CI failure may still happen due to a number of reasons, for example:

    • Possibly due to a silent merge conflict (the changes in this pull request being incompatible with the current code in the target branch). If so, make sure to rebase on the latest commit of the target branch.

    • A sanitizer issue, which can only be found by compiling with the sanitizer and running the affected test.

    • An intermittent issue.

    Leave a comment here, if you need help tracking down a confusing failure.

    </details>

  77. DrahtBot removed the label CI failed on Oct 1, 2026
  78. l0rinc renamed this:
    refactor: optimize block index comparisons (1.4-6.8x faster)
    validation: reduce block index comparison overhead
    on Oct 4, 2026
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