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Rollup merge of rust-lang#113529 - oli-obk:simd_shuffle_evaluated, r=…
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…wesleywiser

Permit pre-evaluated constants in simd_shuffle

fixes rust-lang#113500
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matthiaskrgr authored Jul 13, 2023
2 parents 3f539cd + 5465748 commit 83fb198
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14 changes: 14 additions & 0 deletions compiler/rustc_codegen_ssa/src/mir/constant.rs
Original file line number Diff line number Diff line change
Expand Up @@ -67,6 +67,20 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
) -> Result<Option<ty::ValTree<'tcx>>, ErrorHandled> {
let uv = match constant.literal {
mir::ConstantKind::Unevaluated(uv, _) => uv.shrink(),
mir::ConstantKind::Ty(c) => match c.kind() {
// A constant that came from a const generic but was then used as an argument to old-style
// simd_shuffle (passing as argument instead of as a generic param).
rustc_type_ir::ConstKind::Value(valtree) => return Ok(Some(valtree)),
other => span_bug!(constant.span, "{other:#?}"),
},
// We should never encounter `ConstantKind::Val` unless MIR opts (like const prop) evaluate
// a constant and write that value back into `Operand`s. This could happen, but is unlikely.
// Also: all users of `simd_shuffle` are on unstable and already need to take a lot of care
// around intrinsics. For an issue to happen here, it would require a macro expanding to a
// `simd_shuffle` call without wrapping the constant argument in a `const {}` block, but
// the user pass through arbitrary expressions.
// FIXME(oli-obk): replace the magic const generic argument of `simd_shuffle` with a real
// const generic.
other => span_bug!(constant.span, "{other:#?}"),
};
let uv = self.monomorphize(uv);
Expand Down
19 changes: 19 additions & 0 deletions tests/ui/simd/shuffle.rs
Original file line number Diff line number Diff line change
@@ -1,14 +1,21 @@
//run-pass
#![feature(repr_simd, platform_intrinsics)]
#![allow(incomplete_features)]
#![feature(adt_const_params)]

extern "platform-intrinsic" {
fn simd_shuffle<T, I, U>(a: T, b: T, i: I) -> U;
fn simd_shuffle16<T, U>(x: T, y: T, idx: [u32; 16]) -> U;
}

#[derive(Copy, Clone)]
#[repr(simd)]
struct Simd<T, const N: usize>([T; N]);

pub unsafe fn __shuffle_vector16<const IDX: [u32; 16], T, U>(x: T, y: T) -> U {
simd_shuffle16(x, y, IDX)
}

fn main() {
const I1: [u32; 4] = [0, 2, 4, 6];
const I2: [u32; 2] = [1, 5];
Expand All @@ -21,4 +28,16 @@ fn main() {
let y: Simd<u8, 2> = simd_shuffle(a, b, I2);
assert_eq!(y.0, [1, 5]);
}
// Test that an indirection (via an unnamed constant)
// through a const generic parameter also works.
// See https://github.com/rust-lang/rust/issues/113500 for details.
let a = Simd::<u8, 16>([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]);
let b = Simd::<u8, 16>([16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31]);
unsafe {
__shuffle_vector16::<
{ [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16] },
Simd<u8, 16>,
Simd<u8, 16>,
>(a, b);
}
}

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