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git_commit commit e8f61801c6237e56b3d69190af7a7acfdcede1e8
Author: Christopher Di Bella <cjdb@google.com>
Date: Fri Sep 12 06:33:10 2025 -0700

[libcxx] adds size-based `__split_buffer` representation to unstable ABI (#139632)

**tl;dr** We can significantly improve the runtime performance of
`std::vector` by changing its representation from three pointers to one
pointer and two integers. This document explains the details of this
change, along with the justifications for making it. See the [RFC] for
more information.

`vector` depends on `__split_buffer` for inserting elements. Changing
`__split_buffer` to match `vector`'s representation simplifies the
model, as it eliminates the need to convert between two different
representations of a contiguous buffer in the same configuration of
libc++.

[RFC]: https://discourse.llvm.org/t/adding-a-size-based-vector-to-libc-s-unstable-abi/86306

---------

Co-authored-by: Jorge Gorbe Moya <jgorbe@google.com>
Filter

ldionne-old-macbook-results test results

Run Order Start Time Duration
Current 552339 2025-12-16T16:40:01 0:00:00
Previous 552902 2025-12-16T16:40:01 0:00:00
Baseline 485288 2025-12-16T16:40:01 0:00:00


Tests Summary

Status Group # # (B)
Performance Regressions 8 0
Added Tests 0 15
Unchanged Tests 67 60
Total Tests 75

Performance Regressions - execution_time Δ Previous Current σ Δ (B) σ (B)
706_stockfish_r 3.40% 21.418 22.146 - 0.00% -
727_cppcheck_r 2.90% 24.343 25.049 - 0.00% -
729_abc_r 2.31% 18.404 18.830 - 0.00% -
707_ntest_r 1.82% 17.877 18.202 - 0.00% -
710_omnetpp_r 1.77% 8.297 8.443 - 0.00% -
737_gmsh_r 1.76% 12.781 13.006 - 0.00% -
766_femflow_r 1.57% 12.784 12.985 - 0.00% -
709_cactus_r 1.55% 19.458 19.760 - 0.00% -

Added Tests - execution_time
706_stockfish_r
707_ntest_r
709_cactus_r
710_omnetpp_r
721_gcc_r
723_llvm_r
727_cppcheck_r
729_abc_r
731_astcenc_r
736_ocio_r
737_gmsh_r
748_flightdm_r
750_sealcrypto_r
753_ns3_r
766_femflow_r


Report Time: 0.69s
Name Current %
706_stockfish_r 22.146 3.40%
707_ntest_r 18.202 1.82%
709_cactus_r 19.760 1.55%
710_omnetpp_r 8.443 1.77%
721_gcc_r 12.991 -
723_llvm_r 11.570 -
727_cppcheck_r 25.049 2.90%
729_abc_r 18.830 2.31%
731_astcenc_r 10.051 -
736_ocio_r 16.261 -
737_gmsh_r 13.006 1.76%
748_flightdm_r 8.893 -
750_sealcrypto_r 18.571 -
753_ns3_r 10.395 -
766_femflow_r 12.985 1.57%
Geometric Mean 14.353 1.17%