Integer bitwise rotate miscompilation

[Alexander Averyanov]

Expected Behaviour

Bitwise rotating works correctly.

Example & Steps To Reproduce

I was porting SHA512 and this function worked differently on CPU and GPU:

fn big_sigma0(x: u64) -> u64 {
    x.rotate_right(28) ^ x.rotate_right(34) ^ x.rotate_right(39)
}

System Info

• Rust: rustc 1.69.0-nightly (44cfafe2f 2023-03-03)
• OS: NixOS Linux 5.15.110
• GPU: AMD Radeon RX 6800 XT
• GPU Driver: amdvlk
• SPIR-V: v2023.2 unknown hash, 1980-01-01T00:00:00 (incorrect time because of NixOS)

[Schell Carl Scivally]

Just FYI the same thing happens with u32.

[Eduard-Mihai Burtescu]

I think @chrisliebaer just ran into the same issue, and AFAICT it's just this being flipped:

rust-gpu/crates/rustc_codegen_spirv/src/builder/mod.rs

Lines 243 to 247 in e96418f

 let mask_is_zero = self 
     .emit() 
     .i_not_equal(bool, None, mask_shift.def(self), zero.def(self)) 
     .unwrap() 
     .with_type(bool); 

(based on the name it should clearly be == not !=)