Files
carbon-lang/toolchain
Chandler Carruth ae4be1be14 Use inline small storage for small SemIR ID sets in toolchain (#7796)
Apply SmallSize = 16 to frequent identifier and instruction/function
sets in ScopeStack, Class, FacetType, and SpecificCoalescer to avoid
dynamic heap allocations on small scopes. Also defer dest_field_names
set allocation in struct conversion and provide default KeyContext for
SetBase. This was found by inspection, but does seem to be a clear 1.5%
win on overall compile time.

```
Ran baseline and experiment 10 times on 128 x 2450 MHz CPUs
CPU caches:
  L1 Data 32Ki
  L1 Instruction 32Ki
  L2 Unified 512Ki
  L3 Unified 32Mi
Load avg: 1.2041 1.16895 2.86133
Computing statistically significant deltas only wherethe P-value < 𝛂 of 0.05
Metric key:
   BenchmarkName... 👍 <delta>    p=<U-test P-value>
          baseline:    <median> ± <% at 95th conf>
        experiment:    <median> ± <% at 95th conf>

 Benchmark                                                      ┃          CPU Time          ┃           CYCLES           ┃       INSTRUCTIONS        ┃          Lines
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━━━━
 BM_CompileApiFileDenseDecls<Lang::Carbon, Phase::Check>/256... │ 👍  -1.768%      p=0.0346  │ 👍  -1.683%      p=0.0346  │ 👍   0.160%    p=0.000428 │ ~
                                                      baseline: │     49.11  ms  ±   1.363%  │    155.6   M   ±   1.875%  │    293.9   M ±   0.015%   │     4.093 k ±   1.360%
                                                    experiment: │     48.24  ms  ±   2.213%  │    153     M   ±   2.465%  │    293.4   M ±   0.081%   │     4.166 k ±   2.165%
                                                                │                            │                            │                           │
 BM_CompileApiFileDenseDecls<Lang::Carbon, Phase::Check>/1024.. │      ??          p=0.159   │      ??          p=0.067   │ 👍   0.153%    p=0.000249 │ ~
                                                      baseline: │     50.61  ms  ±   2.379%  │    160.7   M   ±   2.777%  │    309.7   M ±   0.015%   │    19.96  k ±   2.326%
                                                    experiment: │     50.32  ms  ±   0.971%  │    159.6   M   ±   0.787%  │    309.2   M ±   0.086%   │    20.07  k ±   0.980%
                                                                │                            │                            │                           │
 BM_CompileApiFileDenseDecls<Lang::Carbon, Phase::Check>/4096.. │ 👍  -1.593%      p=0.0112  │ 👍  -1.632%      p=0.00743 │ 👍   0.138%    p=0.000328 │ ~
                                                      baseline: │     58.58  ms  ±   1.673%  │    186.5   M   ±   1.487%  │    371.2   M ±   0.102%   │    70.96  k ±   1.645%
                                                    experiment: │     57.65  ms  ±   1.032%  │    183.5   M   ±   1.079%  │    370.7   M ±   0.091%   │    72.11  k ±   1.043%
                                                                │                            │                            │                           │
 BM_CompileApiFileDenseDecls<Lang::Carbon, Phase::Check>/16384. │ 👍  -1.695%      p=0.029   │ 👍  -1.823%      p=0.0411  │ 👍   0.221%    p=0.000428 │ ~
                                                      baseline: │     90.07  ms  ±   3.686%  │    287.1   M   ±   3.694%  │    618.9   M ±   0.106%   │   186.9   k ±   3.555%
                                                    experiment: │     88.55  ms  ±   1.891%  │    281.8   M   ±   2.142%  │    617.6   M ±   0.158%   │   190.1   k ±   1.856%
                                                                │                            │                            │                           │
 BM_CompileApiFileDenseDecls<Lang::Carbon, Phase::Check>/65536. │ 👍  -1.797%      p=0.0201  │ 👍  -1.762%      p=0.0201  │ 👍   0.222%    p=0.000328 │ ~
                                                      baseline: │    222.1   ms  ±   2.560%  │    711     M   ±   2.417%  │      1.613 G ±   0.158%   │   304.2   k ±   2.496%
                                                    experiment: │    218.1   ms  ±   1.950%  │    698.5   M   ±   2.010%  │      1.61  G ±   0.075%   │   309.7   k ±   1.989%
                                                                │                            │                            │                           │
 BM_CompileApiFileDenseDecls<Lang::Carbon, Phase::Check>/262144 │      ??          p=0.398   │      ??          p=0.36    │ 👍   0.166%    p=0.000931 │ ~
                                                      baseline: │    782.2   ms  ±   2.666%  │      2.502 G   ±   2.546%  │      5.596 G ±   0.038%   │   345.8   k ±   2.597%
                                                    experiment: │    780.6   ms  ±   4.249%  │      2.483 G   ±   4.691%  │      5.587 G ±   0.024%   │   346.5   k ±   4.075%
                                                                │                            │                            │                           │
```

Assisted-by: Antigravity with Gemini
2026-09-17 15:49:43 +00:00
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