We've seen the same on an internal codebase during aarch64 builds. Anecdotally, it seems like the two steps that seemed to drag on were linking and "Wrapping AST for [target] for debugging". Haven't yet tried with a top-of-tree build newer than 2021-11-20.

Comment by Reid Nantes (JIRA)

Swift Development Snapshot 2021-12-06 still has this issue

This is an LLVM issue with GlobalISel. See llvm/llvm-project#53109 for more information

Comment by Reid Nantes (JIRA)

Swift Development Snapshot 2022-01-09 still has this issue

rnantes (JIRA User) It uses the same revision of LLVM, so nothing changed

Comment by Reid Nantes (JIRA)

@asl Posted just to show this issue still is relevant. I've also posted in the [Swift Forums | https://forums.swift.org/t/major-compile-performance-regression-swift-5-6/54604]

@swift-ci create

Ok, here is the full story. The issue was exposed by LLVM mainline d0af732 and subsequently fixed in LLVM mainline by 64bef13. The underlying issue seems to be quite clear.

Swift is currently using stable/20210726 branch, so was unlucky enough to make this branch in a ~3 week window between these changes 🙂

I submitted apple#3804 which backports 64bef13 to stable/20210726 branch

The PR was merged. Likely it should be cherry-picked to an appropriate Swift 5.6 branches.

Backport to swift/release/5.6 submitted in apple/llvm-project#3853

rnantes (JIRA User) Will you please confirm that the issue had gone with the latest swift nightly snapshot? So we can close this issue.

Thanks!

Comment by Reid Nantes (JIRA)

I can confirm this now works as expected on the latest swift nightly snapshot. Thank you @asl for your work this.