rust-lang / rust-lang/portable-simd
Ensure `load`s of vector types have `!noundef`
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Description
Assuming that -- like __m128 -- a u32x4 isn't actually allowed to be undef, we should ensure that we have !noundef metadata on the corresponding loads. (This assumes Simd<MaybeUninit<u32>, 4> would be needed for real uninit.)
It looks like today https://rust.godbolt.org/z/hs1MKh15x we don't:
%_8 = load <2 x i32>, ptr %self, align 8
%_9 = load <2 x i32>, ptr %other, align 8
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the linked Rust Compiler Explorer example and inspecting its LLVM output, especially the vector loads shown in the issue. Trace how these loads are generated and verify that the corresponding loads carry !noundef metadata when the change is complete.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100