`powi` miscompiles on x86 uefi targets

[usamoi]

I tried this code:

#[no_mangle]
fn f(x: f32, n: i32) -> f32 {
    x.powi(n)
}

cargo build --target x86_64-unknown-uefi

I expected to see this happen: it compiles and works

Since 1.87

Instead, it compiles to

std::f32::<impl f32>::powi::hc33784da3254b978:
        sub     rsp, 16
        mov     dword ptr [rsp + 4], ecx
        mov     dword ptr [rsp + 8], edx
        mov     eax, dword ptr [rsp + 12]
        add     rsp, 16
        ret

Before 1.87

Instead, this happened:

error: Don't know how to soften fpowi to fpow

Same error on i686-unknown-uefi, but not on aarch64-unknown-uefi.

Meta

rustc --version --verbose:

rustc 1.83.0 (90b35a623 2024-11-26)
binary: rustc
commit-hash: 90b35a6239c3d8bdabc530a6a0816f7ff89a0aaf
commit-date: 2024-11-26
host: x86_64-unknown-linux-gnu
release: 1.83.0
LLVM version: 19.1.1

[bjorn3]

LLVM is missing a soft-float implementation for fpowi: https://github.com/llvm/llvm-project/blob/eb812d28f542bf0de54c157a7391e446739570cc/llvm/lib/CodeGen/SelectionDAG/LegalizeFloatTypes.cpp#L725-L727

[usamoi]

It compiles with a custom target with llvm-target set to x86_64-unknown-uefi, so #132570 should help fix this.

This method does not work for i686-unknown-uefi. I see error: rustc interrupted by SIGSEGV, printing backtrace using a custom target.

[folkertdev]

Looks like this is fixed https://godbolt.org/z/b7h9qEa5P since 1.87 (so probably llvm 20)

[usamoi]

Looks like this is fixed https://godbolt.org/z/b7h9qEa5P since 1.87 (so probably llvm 20)

rustc no longer crashes, but we are still getting a miscompilation.