Make debugger significantly faster (backport #12645)#12746
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mergify[bot] merged 4 commits into2.25-maintenancefrom Mar 24, 2025
Merged
Make debugger significantly faster (backport #12645)#12746mergify[bot] merged 4 commits into2.25-maintenancefrom
mergify[bot] merged 4 commits into2.25-maintenancefrom
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All of this code doesn't actually depend on anything from libexpr. Because Pos is so tigtly coupled with Error, it makes sense to have in the same library. (cherry picked from commit a53b184)
This should provide context for follow-up commits in the patch series. (cherry picked from commit bf12aed)
Previous implementation didn't actually check if
std::get_if returned a nullptr:
std::optional<SourcePath> getSourcePath() const {
return *std::get_if<SourcePath>(&origin);
}
(cherry picked from commit 50123f2)
The underlying issue is that debugger code path was calling PosTable::operator[] in each eval method. This has become incredibly expensive since 5d9fdab. While we are it it, I've reworked the code to not use std::shared_ptr where it really isn't necessary. As I've documented in previous commits, this is actually more a workaround for recursive header dependencies now and is only necessary in `error.hh` code. Some ad-hoc benchmarking: After this commit: ``` Benchmark 1: nix eval nixpkgs#hello --impure --ignore-try --no-eval-cache --debugger Time (mean ± σ): 784.2 ms ± 7.1 ms [User: 561.4 ms, System: 147.7 ms] Range (min … max): 773.5 ms … 792.6 ms 10 runs ``` On master 3604c7c: ``` Benchmark 1: nix eval nixpkgs#hello --impure --ignore-try --no-eval-cache --debugger Time (mean ± σ): 22.914 s ± 0.178 s [User: 18.524 s, System: 4.151 s] Range (min … max): 22.738 s … 23.290 s 10 runs ``` (cherry picked from commit adbd083)
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Motivation
The underlying issue is that debugger code path was
calling
PosTable::operator[]in eachevalmethod.This has become incredibly expensive since 5d9fdab.
While we are it it, I've reworked the code to
not use std::shared_ptr where it really isn't necessary.
As I've documented in previous commits, this is actually
more a workaround for recursive header dependencies now
and is only necessary in
error.hhcode.Some ad-hoc benchmarking:
After this commit:
On master 3604c7c:
Context
nix build --debugger#10796cc @roberth for 50123f2
cc @tomberek, #12544 (comment)
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This is an automatic backport of pull request #12645 done by [Mergify](https://mergify.com).