| Issue |
145121
|
| Summary |
Small arrays of MaybeUninit::<u8>::uninit() are deoptimized to all zeroes
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
saethlin
|
I started by looking at https://github.com/rust-lang/rust/issues/139355 but it looks like the root cause can be produce with much less Rust code: https://godbolt.org/z/4Kv5Gbdse
As far as I can tell, things go wrong twice. SROA tries to splat the undef i8, but it generates a generic sequence of instructions in the process instead of just an undef of the target type. Then EarlyCSE sees the splat and replaces it with a 0.
I have a candidate fix for this, though I'm a bit of a novice at working on LLVM.
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