Inlining + target_feature broken in powerpc64

godbolt

#![feature(repr_simd, powerpc_target_feature)]
#![allow(non_camel_case_types)]

#[repr(simd)] pub struct u32x4(u32, u32, u32, u32);

impl u32x4 {
    #[inline]
    // #[inline(always)]
    fn splat(x: u32) -> Self {
        u32x4(x, x, x, x)
    }
}

#[target_feature(enable = "altivec")]
pub unsafe fn splat_u32x4(x: u32) -> u32x4 {
    u32x4::splat(x)
}

with #[inline] that code produces a function call within splat_u32x4 (b example::u32x4::splat) to u32x4::splat, which is not eliminated, even though this method is module private. With #[inline(always)], u32x4::splat is inlined into splat_u32x4, and no code for u32x4::splat is generated.

#[inline] should not be needed here, much less #[inline(always)], yet without #[inline(always)] this produces bad codegen.

Removing the #[target_feature] attribute from splat_u32x4 fixes the issue, no #[inline] necessary: godbolt. So there must be some interaction between inlining and target features going on here.

This is something on the LLVM side. See this comment. This happens in all microarchitectures except for ARM and x86 I think.

This was resolved in llvm/llvm-project#117493 and llvm/llvm-project#126562
godbolt

Remove workarounds for rust-lang/rust#60637

Rollup merge of rust-lang#151346 - folkertdev:simd-splat, r=workingju…

Unrolled build for #151346

Rollup merge of #151346 - folkertdev:simd-splat, r=workingjubilee

The final macos issue was resolved by

and now produces

mov rbp, rsp
pavgw xmm0, xmm1

Rollup merge of #151346 - folkertdev:simd-splat, r=workingjubilee

Bug 2043090. Patch vendored jxl-rs to work around LLVM/rust issue cau…

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Inlining + target_feature broken in powerpc64 #60637

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Inlining + target_feature broken in powerpc64 #60637

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sayantn commented on Jun 29, 2024

sayantn commented on Apr 13, 2025

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folkertdev commented on Jan 27, 2026

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