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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Nondeterminstic optimization on macOS, unknown where though"
href="https://bugs.llvm.org/show_bug.cgi?id=43909">43909</a>
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<th>Summary</th>
<td>Nondeterminstic optimization on macOS, unknown where though
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Scalar Optimizations
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>alex@crichton.co
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<th>CC</th>
<td>gk@torproject.org, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>The tor project has a bug open -
<a href="https://trac.torproject.org/projects/tor/ticket/32053">https://trac.torproject.org/projects/tor/ticket/32053</a> - that their builds on
macOS are not reproducible. The source of this nondeterminism in the build is
the Rust source code in Firefox. After digging in that thread (there's a lot of
discussion, but feel free to skip over it) we've concluded that the LLVM
optimization passes for a bitcode file are the source of the nondeterminism.
The files hosted at <a href="https://people.torproject.org/~gk/misc/32053/">https://people.torproject.org/~gk/misc/32053/</a> are produced
by rustc itself, and style.no-opt.bc has been seen to optimize to style1.bc and
style2.bc. Locally I've checked the latest commit of LLVM and this command
produces different hashes:
opt -O3 style.no-opt.bc -o foo.bc
Using LLVM trunk I'm seeing two sha1 hashes show up:
* 045fb2b4a581418e0287e208e1d4633804b7e2db
* 6887c6a5d427aa792b51188c2e27521392a1d048
One is more likely than the other, but this appears to be at least one source
of nondeterminism in the build of Tor.
Unfortunately the `style.no-opt.bc` file is 90MB large (!) which means that I'm
still in the process of reducing this to something more digestable. Running
`opt -O3` once on the file takes a few minutes, though, so my attempts at using
`bugpoint` are likely going to take quite awhile. In the meantime though I
wanted to open up this bug to see if others know better how to debug this
and/or minimize it.
If more information is needed about the non-determinism, please just let me
know as well!</pre>
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