alexfh wrote:
So, what's happening here is a significant increase in the compilation time of
a pretty large source that has a large number of modular dependencies (using
Clang header modules rather than C++20 modules).
The times reported by `clang -ftime-report` for clang frontend change
drastically:
before this commit:
```
===-------------------------------------------------------------------------===
Clang front-end time report
===-------------------------------------------------------------------------===
Total Execution Time: 207.1765 seconds (218.7714 wall clock)
---User Time--- --System Time-- --User+System-- ---Wall Time--- ---
Name ---
153.2751 ( 78.6%) 8.5109 ( 70.4%) 161.7860 ( 78.1%) 170.5710 ( 78.0%)
Clang front-end timer
40.0169 ( 20.5%) 3.1469 ( 26.0%) 43.1638 ( 20.8%) 45.8168 ( 20.9%)
Reading modules
```
after this commit:
```
===-------------------------------------------------------------------------===
Clang front-end time report
===-------------------------------------------------------------------------===
Total Execution Time: 1134.1241 seconds (1179.8429 wall clock)
---User Time--- --System Time-- --User+System-- ---Wall Time---
--- Name ---
591.7280 ( 54.0%) 21.5861 ( 56.0%) 613.3141 ( 54.1%) 638.4518 ( 54.1%)
Clang front-end timer
502.9522 ( 45.9%) 16.6865 ( 43.3%) 519.6387 ( 45.8%) 540.1083 ( 45.8%)
Reading modules
```
Given the notorious difficulty in preparing shareable test cases for modular
compilations, I expect this to take days until we can give you something
specific, but I'll ask @ilya-biryukov if he can spot something right away.
And I suspect that ARM is a red herring here. The problem seems to be purely in
Clang frontend. Checking...
https://github.com/llvm/llvm-project/pull/92083
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