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git_commit commit 4c5877dbc2127e4948b9ef9a8c0beb4dd4b1fcf0
Author: Nikolas Klauser <nikolasklauser@berlin.de>
Date: Fri Aug 29 18:48:11 2025 +0200

[libc++] Optimize map::insert_or_assign (#155816)

`__emplace_unique` uses `__find_equal`, which can be significantly
faster than `lower_bound`. As a nice side-effect, this also changes the
implementation to the "naive" implementation of trying `insert` first,
and if that fails assign instead. This also matches the
`insert_or_assign` overloads with a hint.

```
Zen 2:
--------------------------------------------------------------------------------------------------------
Benchmark old new
--------------------------------------------------------------------------------------------------------
std::map<int, int>::insert_or_assign(key, value) (already present)/0 1.62 ns 1.53 ns
std::map<int, int>::insert_or_assign(key, value) (already present)/32 5.78 ns 5.99 ns
std::map<int, int>::insert_or_assign(key, value) (already present)/1024 21.5 ns 15.4 ns
std::map<int, int>::insert_or_assign(key, value) (already present)/8192 26.2 ns 20.5 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/0 22.5 ns 21.1 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/32 42.9 ns 28.4 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/1024 118 ns 92.0 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/8192 227 ns 173 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/0 13.2 ns 18.9 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/32 65.6 ns 39.0 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/1024 127 ns 64.4 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/8192 134 ns 71.4 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/0 45.6 ns 37.3 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/32 142 ns 93.3 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/1024 288 ns 147 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/8192 368 ns 182 ns

Apple M4:
--------------------------------------------------------------------------------------------------------
Benchmark old new
--------------------------------------------------------------------------------------------------------
std::map<int, int>::insert_or_assign(key, value) (already present)/0 0.784 ns 0.740 ns
std::map<int, int>::insert_or_assign(key, value) (already present)/32 2.52 ns 1.77 ns
std::map<int, int>::insert_or_assign(key, value) (already present)/1024 8.72 ns 4.06 ns
std::map<int, int>::insert_or_assign(key, value) (already present)/8192 10.6 ns 3.98 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/0 17.3 ns 17.2 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/32 22.5 ns 19.3 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/1024 56.8 ns 33.5 ns
std::map<int, int>::insert_or_assign(key, value) (new value)/8192 88.2 ns 41.0 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/0 16.6 ns 11.8 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/32 13.7 ns 30.7 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/1024 46.7 ns 49.1 ns
std::map<std::string, int>::insert_or_assign(key, value) (already present)/8192 41.9 ns 76.9 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/0 40.0 ns 40.5 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/32 38.9 ns 40.0 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/1024 84.9 ns 96.9 ns
std::map<std::string, int>::insert_or_assign(key, value) (new value)/8192 166 ns 149 ns
```
Filter

ldionne-old-macbook-results test results

Run Order Start Time Duration
Current 550580 2025-12-16T16:40:01 0:00:00
Previous 550572 2025-12-16T16:40:01 0:00:00
Baseline 485288 2025-12-16T16:40:01 0:00:00


Tests Summary

Status Group # # (B)
Performance Improvements 4 0
Added Tests 1 17
Unchanged Tests 80 68
Total Tests 85

Performance Improvements - execution_time Δ Previous Current σ Δ (B) σ (B)
737_gmsh_r -4.92% 13.273 12.620 0.253 0.00% 0.253
707_ntest_r -2.02% 18.391 18.019 0.098 0.00% 0.098
748_flightdm_r -1.83% 9.085 8.919 0.048 0.00% 0.048
709_cactus_r -1.62% 20.025 19.701 0.072 0.00% 0.072

Added Tests - execution_time
735_gem5_r

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
734_vpr_r
735_gem5_r
736_ocio_r
737_gmsh_r
748_flightdm_r
750_sealcrypto_r
753_ns3_r
766_femflow_r


Report Time: 0.09s
Name Current %
706_stockfish_r 22.134 -
707_ntest_r 18.019 -2.02%
709_cactus_r 19.701 -1.62%
710_omnetpp_r 8.390 -
721_gcc_r 12.993 -
723_llvm_r 11.464 -
727_cppcheck_r 24.139 -
729_abc_r 18.626 -
731_astcenc_r 10.142 -
734_vpr_r 15.137 -
735_gem5_r 13.592 -
736_ocio_r 16.235 -
737_gmsh_r 12.620 -4.92%
748_flightdm_r 8.919 -1.83%
750_sealcrypto_r 18.515 -
753_ns3_r 10.419 -
766_femflow_r 12.839 -
Geometric Mean 14.260 -2.06%