[Bug libstdc++/96942] std::pmr::monotonic_buffer_resource causes CPU cache misses

[dmitriy.ovdienko at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96942

--- Comment #27 from Dmitriy Ovdienko <dmitriy.ovdienko at gmail dot com> ---
Following are CPU counters I've got for improved C++ test vs Rust and original
C++ test by Danial Klimkin

| CPU counter      |           Rust |     C++ before |        C++ now |
|------------------|---------------:|---------------:|---------------:|
| cache-references |     29,949,104 |     46,639,647 |     60,495,704 |
| cache-misses     |     12,378,855 |     24,667,211 |     25,741,109 |
| cycles           | 24,700,616,015 | 20,066,358,482 | 23,714,062,385 |
| instructions     | 31,819,068,745 | 30,416,793,570 | 30,455,923,689 |
| branches         |  4,835,891,456 |  4,829,846,926 |  4,832,915,354 |
| branch-misses    |     10,768,008 |     11,313,719 |     11,643,211 |
| faults           |         82,346 |        234,891 |        239,866 |
| migrations       |              2 |              4 |             21 |
| Time-elapsed     |         2.0779 |         2.0884 |         2.0061 |
| Seconds-user     |         7.1599 |         5.5976 |         6.5808 |
| Seconds-sys      |         0.1803 |         0.3678 |         0.4595 |