[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 alexcrichton):

 Oh so for just `-jump-threading` to work you'll need to do:

 1. Start with `foo.bc`
 2. Figure out smallest N where `opt -O3 foo.bc -opt-bisect-limit` is non-
 deterministic
 3. Run `opt -O3 -o input.bc -opt-bisect-limit=N-1 foo.bc`
 4. Use `llvm-extract` on `input.bc` to extract the function
 5. Run `opt -jump-threading` over the extracted `*.bc` file

 You won't be able to run `-jump-threading` over the original module,
 you'll need to run it over the module just before the output becomes
 nondeterministic.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32053#comment:39>
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