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commit f02b661054547b423177c9498cdb554f5036a3e0 Author: Adrian Vogelsgesang <avogelsgesang@salesforce.com> Date: Mon Nov 3 12:18:43 2025 -0800 [libc++] Add move constructor & assignment to `exception_ptr` (#164281) This commit adds move constructor, move assignment and `swap` to `exception_ptr`. Adding those operators allows us to avoid unnecessary calls to `__cxa_{inc,dec}rement_refcount`. Performance results (from libc++'s CI): ``` Benchmark Baseline Candidate Difference % Difference ------------------------------------ ---------- ----------- ------------ -------------- bm_exception_ptr_copy_assign_nonnull 9.77 9.94 0.18 1.79% bm_exception_ptr_copy_assign_null 10.29 10.65 0.35 3.42% bm_exception_ptr_copy_ctor_nonnull 7.02 7.01 -0.01 -0.13% bm_exception_ptr_copy_ctor_null 10.54 10.60 0.06 0.56% bm_exception_ptr_move_assign_nonnull 16.92 13.76 -3.16 -18.70% bm_exception_ptr_move_assign_null 10.61 10.76 0.14 1.36% bm_exception_ptr_move_ctor_nonnull 13.31 10.25 -3.06 -23.02% bm_exception_ptr_move_ctor_null 10.28 7.30 -2.98 -28.95% bm_exception_ptr_swap_nonnull 19.22 0.63 -18.59 -96.74% bm_exception_ptr_swap_null 20.02 7.79 -12.23 -61.07% ``` As expected, the `bm_exception_ptr_copy_*` benchmarks are not influenced by this change. `bm_exception_ptr_move_*` benefits between 18% and 30%. The `bm_exception_ptr_swap_*` tests show the biggest improvements since multiple calls to the copy constructor are replaced by a simple pointer swap. While `bm_exception_ptr_move_assign_null` did not show a regression in the CI measurements, local measurements showed a regression from 3.98 to 4.71, i.e. by 18%. This is due to the additional `__tmp` inside `operator=`. The destructor of `__other` is a no-op after the move because `__other.__ptr` will be a nullptr. However, the compiler does not realize this, since the destructor is not inlined and is lacking a fast-path. As such, the swap-based implementation leads to an additional destructor call. `bm_exception_ptr_move_assign_nonnull` still benefits because the swap-based move constructor avoids unnecessary __cxa_{in,de}crement_refcount calls. As soon as we inline the destructor, this regression should disappear again. Works towards #44892 |
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ldionne-old-macbook-results test results
| Run | Order | Start Time | Duration |
|---|---|---|---|
| Current | 558049 | 2025-12-16T16:40:01 | 0:00:00 |
| Previous | 558049 | 2025-12-16T16:40:01 | 0:00:00 |
| Baseline | 485288 | 2025-12-16T16:40:01 | 0:00:00 |
Tests Summary
| Status Group | # | # (B) |
|---|---|---|
| Added Tests | 0 | 16 |
| Unchanged Tests | 80 | 64 |
| Total Tests | 80 |
| 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 |
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