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| git_commit |
commit d200df0557b71fae0d77bc7fc1650d22a05af371 Author: Aiden Grossman <aidengrossman@google.com> Date: Mon Nov 3 11:04:22 2025 -0800 [libcxx] Remove Redundant Reset in ~basic_string (#164718) 8dae17be2991cd7f0d7fd9aa5aecd064520a14f6 refactors basic_string for more code reuse. This makes sense in most cases, but has performance overhead in the case of ~basic_string. The refactoring of ~basic_string to call __reset_internal_buffer() added a redundant (inside the destructor) reset of the object, which the optimizer is unable to optimize away in many cases. This patch prevents a ~1% regression we observed on an internal workload when applying the original refactoring. This does slightly pessimize the code readability, but I think this change is worth it given the performance impact. I'm hoping to add a benchmark(s) to the upstream libc++ benchmark suite around string construction/destruction to ensure that this case does not regress as it seems common in real world applications. I will put up a separate PR for that when I figure out a reasonable way to write it. |
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ldionne-old-macbook-results test results
| Run | Order | Start Time | Duration |
|---|---|---|---|
| Current | 558036 | 2025-12-16T16:40:01 | 0:00:00 |
| Previous | 558006 | 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 | 1 | 0 |
| Performance Improvements | 1 | 0 |
| Added Tests | 0 | 16 |
| Unchanged Tests | 78 | 64 |
| Total Tests | 80 |
| Performance Regressions - execution_time | Δ | Previous | Current | σ | Δ (B) | σ (B) |
|---|---|---|---|---|---|---|
| 748_flightdm_r | 1.56% | 8.864 | 9.002 | - | 0.00% | - |
| Performance Improvements - execution_time | Δ | Previous | Current | σ | Δ (B) | σ (B) |
|---|---|---|---|---|---|---|
| 753_ns3_r | -2.32% | 10.254 | 10.016 | - | 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 |
| 735_gem5_r |
| 736_ocio_r |
| 737_gmsh_r |
| 748_flightdm_r |
| 750_sealcrypto_r |
| 753_ns3_r |
| 766_femflow_r |
Report Time: 0.64s