Bug ID: 37039
Summary: [PowerPC, bisected] miscompilation in rust crate
Component: Backend: PowerPC
CC: email@example.com, nemanja.i....@gmail.com
Created attachment 20170
proposed fix: convert RLDICLo using a 64-bit InVal too
We found one test case in the "futures" crate that started failing on ppc64
when we upgraded to Rust 1.25 with LLVM 6.0 (Fedora's LLVM, not Rust's fork).
The same test case still passes with Rust 1.25 and LLVM 5.0.
I bisected this to https://reviews.llvm.org/D41369. You can find IR and
binaries before and after that commit on the rhbz, but I didn't figure out an
easy way to reproduce this directly. I went through the whole motion of
building LLVM, building rustc with that LLVM, then running the "futures" tests.
The attached patch seems to solve it, using a 64-bit value for PPC::RLDICLo in
PPCInstrInfo::convertToImmediateForm. I don't know enough about LLVM or PPC to
distill a proper test though, so I hope someone who knows the platform better
can figure that out.
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