Improve sharing in `ModIface` after generation
Summary
Generation of ModIface can contain many duplicates, as demonstrated in #24540 (closed), especially when -fwrite-if-simplified-core was used, which embeds core expressions into the interface file.
This allows for much faster GHCi startups and also promises improved compilation performance during normal compilation (tbh, I haven't benchmarked this in particular, but it makes sense to me ;) )
To improve the sharing of ModIface, and thus reducing the memory footprint during compilation, we can use the serialisation mechanism of ModIface to achieve the same memory footprint improvement as in !12371 (closed), but for .hi file generation (again, assuming -fwrite-if-simplified-core is used).
We implemented this improvement and benchmarked it against GHC head (3fff0977). The benchmark was run on the agda codebase, using the following command (omitting the compilation options of agda):
$ ghci -fforce-recomp -fwrite-if-simplified-core +RTS -tprofile -i0.5The results look as follows:
| ghc | compression level | allocated | peak_allocated | all_seconds | cpu_seconds | hi file size |
|---|---|---|---|---|---|---|
| ghc head | 1 | 65.6 GB | 2218 MB | 46.21 s | 45.60 s | 101.7 MB |
| ghc with sharing | 1 | 66.0 GB | 2259 MB | 47.29 s | 46.69 s | 101.7 MB |
| ghc with sharing | 2 | 66.6 GB | 1984 MB | 46.08 s | 45.52 s | 25.2 MB |
| ghc with sharing | 3 | 66.6 GB | 1534 MB | 47.51 s | 46.89 s | 24.2 MB |
The compression level is the flag -fwrite-if-compression which is introduced in !12371 (closed).