Fangrui Song a24418375a [CodeLayout] cache-directed sort: limit max chain size (#69039) ...

When linking an executable with a slightly larger executable,
ld.lld --call-graph-profile-sort=cdsort can be very slow (see #68638).
```
   4.6%  20.7Mi    .text.hot
   3.5%  15.9Mi    .text
   3.4%  15.2Mi    .text.unknown
```

Add cl option `cdsort-max-chain-size`, which is similar to
`ext-tsp-max-chain-size`, and set it to 128, to improve performance.

In `ld.lld @response.txt --threads=4 --call-graph-profile-sort=cdsort
--time-trace"
builds, the "Total Sort sections" time is measured as follows:

* -mllvm  -cdsort-max-chain-size=64: 1.321813
* -mllvm -cdsort-max-chain-size=128: 2.030425
* -mllvm -cdsort-max-chain-size=256: 2.927684
* -mllvm -cdsort-max-chain-size=512: 5.493106
* unlimited: 9 minutes

The rest part takes 6.8s.

2023-10-22 16:50:03 -07:00

2.8 KiB

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