https://bugs.llvm.org/show_bug.cgi?id=43909
Bug ID: 43909
Summary: Nondeterminstic optimization on macOS, unknown where
though
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
The tor project has a bug open -
https://trac.torproject.org/projects/tor/ticket/32053 - 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 https://people.torproject.org/~gk/misc/32053/ 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!
--
You are receiving this mail because:
You are on the CC list for the bug._______________________________________________
llvm-bugs mailing list
[email protected]
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
