[tbb-bugs] #32053 [Applications/Tor Browser]: Tor Browser bundles based on Firefox 68 ESR are not reproducible (LLVM optimization issue)

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#32053: Tor Browser bundles based on Firefox 68 ESR are not reproducible (LLVM
optimization issue)
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 Reporter:  gk                                   |          Owner:  tbb-
                                                 |  team
     Type:  defect                               |         Status:  new
 Priority:  Immediate                            |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Critical                             |     Resolution:
 Keywords:  TorBrowserTeam201911, tbb-9.0-must,  |  Actual Points:
  tbb-9.0-issues, tbb-regression,                |
  tbb-9.0.1-can, GeorgKoppen201911               |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
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Comment (by gk):

 Replying to [comment:27 alexcrichton]:
 > I just posted a comment on the bug report with a much more minimal test
 case (only a few hundred KB!), it only took many cpu hours to extract :)
 >
 > From here I'm still trying to reduce it further to increase the
 likelihood that someone from LLVM can help fix (I'm not so good at LLVM
 internals). This test case is small enough though that it may be pretty
 reasonable to bisect LLVM itself with. Dealing with a bitcode file across
 that many LLVM revisions may be pretty difficult though, so bisection
 likely won't be trivial.

 Okay, it seems the optimization being the problem here is in -O1, which is
 unfortunate because I had some hope reducing the current -O2 to it could
 be a workaround... I am not sure whether -O0 is worth it. But it might be
 an option if we don't solve the bug until the next planned release.

 I'll set up some bisecting in parallel to your efforts and see whether
 that gets us anywhere. If you get to the problem with `bugpoint` or some
 LLVM dev is helping meanwhile even better. :)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32053#comment:28>
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