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Rollup merge of rust-lang#95961 - RalfJung:gather-scatter, r=workingj…
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…ubilee

implement SIMD gather/scatter via vector getelementptr

Fixes rust-lang/portable-simd#271

However, I don't *really* know what I am doing here... Cc `@workingjubilee` `@calebzulawski`

I didn't do anything for cranelift -- `@bjorn3` not sure if it's okay for that backend to temporarily break. I'm happy to cherry-pick a patch that adds cranelift support. :)
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fee1-dead authored Apr 15, 2022
2 parents b82ae65 + eb905c0 commit 95ec29e
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Showing 6 changed files with 63 additions and 0 deletions.
21 changes: 21 additions & 0 deletions compiler/rustc_codegen_llvm/src/intrinsic.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1839,6 +1839,27 @@ unsupported {} from `{}` with element `{}` of size `{}` to `{}`"#,
simd_neg: Int => neg, Float => fneg;
}

if name == sym::simd_arith_offset {
// This also checks that the first operand is a ptr type.
let pointee = in_elem.builtin_deref(true).unwrap_or_else(|| {
span_bug!(span, "must be called with a vector of pointer types as first argument")
});
let layout = bx.layout_of(pointee.ty);
let ptrs = args[0].immediate();
// The second argument must be a ptr-sized integer.
// (We don't care about the signedness, this is wrapping anyway.)
let (_offsets_len, offsets_elem) = arg_tys[1].simd_size_and_type(bx.tcx());
if !matches!(offsets_elem.kind(), ty::Int(ty::IntTy::Isize) | ty::Uint(ty::UintTy::Usize)) {
span_bug!(
span,
"must be called with a vector of pointer-sized integers as second argument"
);
}
let offsets = args[1].immediate();

return Ok(bx.gep(bx.backend_type(layout), ptrs, &[offsets]));
}

if name == sym::simd_saturating_add || name == sym::simd_saturating_sub {
let lhs = args[0].immediate();
let rhs = args[1].immediate();
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1 change: 1 addition & 0 deletions compiler/rustc_span/src/symbol.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1247,6 +1247,7 @@ symbols! {
simd,
simd_add,
simd_and,
simd_arith_offset,
simd_as,
simd_bitmask,
simd_cast,
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1 change: 1 addition & 0 deletions compiler/rustc_typeck/src/check/intrinsic.rs
Original file line number Diff line number Diff line change
Expand Up @@ -437,6 +437,7 @@ pub fn check_platform_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>)
| sym::simd_fpow
| sym::simd_saturating_add
| sym::simd_saturating_sub => (1, vec![param(0), param(0)], param(0)),
sym::simd_arith_offset => (2, vec![param(0), param(1)], param(0)),
sym::simd_neg
| sym::simd_fsqrt
| sym::simd_fsin
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4 changes: 4 additions & 0 deletions library/portable-simd/crates/core_simd/src/intrinsics.rs
Original file line number Diff line number Diff line change
Expand Up @@ -61,6 +61,10 @@ extern "platform-intrinsic" {
/// xor
pub(crate) fn simd_xor<T>(x: T, y: T) -> T;

/// getelementptr (without inbounds)
#[cfg(not(bootstrap))]
pub(crate) fn simd_arith_offset<T, U>(ptrs: T, offsets: U) -> T;

/// fptoui/fptosi/uitofp/sitofp
/// casting floats to integers is truncating, so it is safe to convert values like e.g. 1.5
/// but the truncated value must fit in the target type or the result is poison.
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11 changes: 11 additions & 0 deletions library/portable-simd/crates/core_simd/src/vector/ptr.rs
Original file line number Diff line number Diff line change
@@ -1,5 +1,8 @@
//! Private implementation details of public gather/scatter APIs.
#[cfg(not(bootstrap))]
use crate::simd::intrinsics;
use crate::simd::{LaneCount, Simd, SupportedLaneCount};
#[cfg(bootstrap)]
use core::mem;

/// A vector of *const T.
Expand All @@ -21,12 +24,16 @@ where
#[inline]
#[must_use]
pub fn wrapping_add(self, addend: Simd<usize, LANES>) -> Self {
#[cfg(bootstrap)]
// Safety: converting pointers to usize and vice-versa is safe
// (even if using that pointer is not)
unsafe {
let x: Simd<usize, LANES> = mem::transmute_copy(&self);
mem::transmute_copy(&{ x + (addend * Simd::splat(mem::size_of::<T>())) })
}
#[cfg(not(bootstrap))]
// Safety: this intrinsic doesn't have a precondition
unsafe { intrinsics::simd_arith_offset(self, addend) }
}
}

Expand All @@ -49,11 +56,15 @@ where
#[inline]
#[must_use]
pub fn wrapping_add(self, addend: Simd<usize, LANES>) -> Self {
#[cfg(bootstrap)]
// Safety: converting pointers to usize and vice-versa is safe
// (even if using that pointer is not)
unsafe {
let x: Simd<usize, LANES> = mem::transmute_copy(&self);
mem::transmute_copy(&{ x + (addend * Simd::splat(mem::size_of::<T>())) })
}
#[cfg(not(bootstrap))]
// Safety: this intrinsic doesn't have a precondition
unsafe { intrinsics::simd_arith_offset(self, addend) }
}
}
25 changes: 25 additions & 0 deletions src/test/codegen/simd_arith_offset.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,25 @@
// compile-flags: -C no-prepopulate-passes
//

#![crate_type = "lib"]
#![feature(repr_simd, platform_intrinsics)]

extern "platform-intrinsic" {
pub(crate) fn simd_arith_offset<T, U>(ptrs: T, offsets: U) -> T;
}

/// A vector of *const T.
#[derive(Debug, Copy, Clone)]
#[repr(simd)]
pub struct SimdConstPtr<T, const LANES: usize>([*const T; LANES]);

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

// CHECK-LABEL: smoke
#[no_mangle]
pub fn smoke(ptrs: SimdConstPtr<u8, 8>, offsets: Simd<usize, 8>) -> SimdConstPtr<u8, 8> {
// CHECK: getelementptr i8, <8 x i8*> %_3, <8 x i64> %_4
unsafe { simd_arith_offset(ptrs, offsets) }
}

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