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Firefox compile time regression #43211
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C-bugCategory: This is a bug.Category: This is a bug.I-compiletimeIssue: Problems and improvements with respect to compile times.Issue: Problems and improvements with respect to compile times.P-mediumMedium priorityMedium priorityT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.Performance or correctness regression from one stable version to another.
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C-bugCategory: This is a bug.Category: This is a bug.I-compiletimeIssue: Problems and improvements with respect to compile times.Issue: Problems and improvements with respect to compile times.P-mediumMedium priorityMedium priorityT-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.Performance or correctness regression from one stable version to another.
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Preliminary note: this may or may not be related to #43141, but just in case, I file this separately instead of piling up there.
I'm sorry I don't have much more fine-grained data at the moment, but -Ztime-passes, when multiple things are built in parallel (while building Firefox), is not entirely helpful, because it doesn't tell to which crate the interleaving numbers belong to.
Rust build times on Firefox are already bad with 1.18. Some of the most time consuming crates have build times that look like the following:
With the latest nightly as of writing (1.20.0-nightly (f85579d 2017-07-12)), those times become:
I'm trying to narrow it down to older nightlies, but it started badly, because I got an ICE building the style crate on the last 1.18.0 nightly (2017-04-29)
Those are times for --release with lto enabled (I have a separate bug to file about lto, but I don't think that's relevant to this regression).
CC: @froydnj, @rillian