Description of problem:
Upstream rust issue 48226 reported a huge regression in compilation time after the update to LLVM 6.0. This was reported in LLVM 36417, which bisected to D38229 as the culprit. D43956 is the upstream LLVM workaround, which Rust has already backported to its own LLVM branch.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Create the project in the Rust bug.
2. "cargo build --release" takes a short time -- about 6 seconds for me.
3. set "debug = true", then "cargo build --release" takes several minutes.
long build time
short build time
This culprit D38229 is in the release_60 branch, but not earlier. I confirmed that using a rust.fc29 build linked to llvm-6 shows the regression, but rust.fc27 linked to llvm-5 is fine.
This should be fixed in rawhide with: llvm-6.0.0-3.fc29
Confirmed! Just updating to this new llvm package solves the slow build.
Shall we keep the bug open, to be closed by a f28 update?
Yes, let's keep it open until the f28 update.
lldb-6.0.0-1.fc28 compiler-rt-6.0.0-1.fc28 libomp-6.0.0-1.fc28 clang-6.0.0-2.fc28 llvm-6.0.0-3.fc28 has been submitted as an update to Fedora 28. https://bodhi.fedoraproject.org/updates/FEDORA-2018-689de58112
clang-6.0.0-2.fc28, compiler-rt-6.0.0-1.fc28, libomp-6.0.0-1.fc28, lldb-6.0.0-1.fc28, llvm-6.0.0-3.fc28 has been pushed to the Fedora 28 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2018-689de58112
clang-6.0.0-2.fc28, compiler-rt-6.0.0-1.fc28, libomp-6.0.0-1.fc28, lldb-6.0.0-1.fc28, llvm-6.0.0-3.fc28 has been pushed to the Fedora 28 stable repository. If problems still persist, please make note of it in this bug report.