[tor-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:  gk
     Type:  defect                               |         Status:
                                                 |  assigned
 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  |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
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Comment (by gk):

 Replying to [comment:43 gk]:
 > Okay, some status update. Bisecting gets hard. I am down to building
 stylo with Rust 1.30.0 and am at LLVM's
 b1546da0e8849d58fcdcf17fa1f2fab0cdae70a4 and have not reached the bottom
 yet.

 Building with Rust 1.29.2 I am down to LLVM's
 8c59921ca3284ced1c358c4c86ec2c830db0bd70 and still have not reached the
 bottom...

 > While exploring ways to move further here I'll investigate whether we
 can just move the `jump-threading` optimization out of `-O1`, say, into
 `-O3` so the we are actually do not use that one.

 I tried that, surprisingly enough that does not fix the issue. I inspected
 the log of the optimization passes that got run and no jump-threading
 showed up (so, that part worked). However, I still got non-reproducible
 outcomes. I gonna ask on the LLVM bug whether that's expected and if not
 whether that could give us some lead where to look closer to understand
 the bug better.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32053#comment:47>
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