GeneralPurposeAllocator.searchBucket: check current bucket before searching the list

[squeek502]

Follow up to #17383. This is a minor optimization that only matters when a small allocation is resized/free'd soon after it is allocated.

The only real difference I was able to observe with this was via a synthetic benchmark that allocates a full bucket and then frees all but one of the slots, over and over in a loop (see "Benchmark code" in #17383):

Debug build:

Benchmark 1 (9 runs): gpa-degen-master.exe
measurement mean ± σ min … max outliers delta
wall_time 575ms ± 5.19ms 569ms … 583ms 0 ( 0%) 0%
peak_rss 43.8MB ± 1.37KB 43.8MB … 43.8MB 1 (11%) 0%
Benchmark 2 (10 runs): gpa-degen-search-cur.exe
measurement mean ± σ min … max outliers delta
wall_time 532ms ± 5.55ms 520ms … 539ms 0 ( 0%) ⚡- 7.5% ± 0.9%
peak_rss 43.8MB ± 65.2KB 43.8MB … 44.0MB 1 (10%) + 0.0% ± 0.1%

ReleaseFast build:

Benchmark 1 (129 runs): gpa-degen-master-release.exe
measurement mean ± σ min … max outliers delta
wall_time 38.9ms ± 1.12ms 36.7ms … 42.4ms 8 ( 6%) 0%
peak_rss 23.2MB ± 2.39KB 23.2MB … 23.2MB 0 ( 0%) 0%
Benchmark 2 (151 runs): gpa-degen-search-cur-release.exe
measurement mean ± σ min … max outliers delta
wall_time 33.2ms ± 999us 31.9ms … 36.3ms 20 (13%) ⚡- 14.7% ± 0.6%
peak_rss 23.2MB ± 2.26KB 23.2MB … 23.2MB 0 ( 0%) + 0.0% ± 0.0%

No difference in Debug mode standard library tests:

Benchmark 1 (10 runs): std-tests-master.exe
measurement mean ± σ min … max outliers delta
wall_time 16.1s ± 224ms 16.0s … 16.7s 1 (10%) 0%
peak_rss 42.3MB ± 4.65KB 42.3MB … 42.3MB 1 (10%) 0%
Benchmark 2 (10 runs): std-tests-search-cur.exe
measurement mean ± σ min … max outliers delta
wall_time 16.0s ± 43.8ms 16.0s … 16.1s 0 ( 0%) - 0.4% ± 0.9%
peak_rss 42.3MB ± 181KB 42.3MB … 42.8MB 1 (10%) + 0.1% ± 0.3%

No noticeable difference in the degraded arocc case from #17383 (this is on Windows with stack trace collection turned off):

Benchmark 1: testaro-suffix.bat master
Time (mean ± σ): 6.658 s ± 0.054 s [User: 5.243 s, System: 1.407 s]
Range (min … max): 6.606 s … 6.746 s 5 runs
Benchmark 2: testaro.bat
Time (mean ± σ): 6.609 s ± 0.055 s [User: 5.124 s, System: 1.451 s]
Range (min … max): 6.540 s … 6.684 s 5 runs
Summary
'testaro.bat' ran
1.01 ± 0.01 times faster than 'testaro-suffix.bat master'