implement simd_shuffle

Author: RalfJung

src/shims/intrinsics.rs

@@ -3,7 +3,7 @@ use std::iter;
 use log::trace;
 
 use rustc_apfloat::{Float, Round};
-use rustc_middle::ty::layout::{IntegerExt, LayoutOf};
+use rustc_middle::ty::layout::{HasParamEnv, IntegerExt, LayoutOf};
 use rustc_middle::{mir, mir::BinOp, ty, ty::FloatTy};
 use rustc_target::abi::{Align, Integer};
 
@@ -614,6 +614,45 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                     this.write_immediate(val, &dest.into())?;
                 }
             }
+            "simd_shuffle" => {
+                let &[ref left, ref right, ref index] = check_arg_count(args)?;
+                let (left, left_len) = this.operand_to_simd(left)?;
+                let (right, right_len) = this.operand_to_simd(right)?;
+                let (dest, dest_len) = this.place_to_simd(dest)?;
+
+                // `index` is an array, not a SIMD type
+                let ty::Array(_, index_len) = index.layout.ty.kind() else {
+                    bug!("simd_shuffle index argument has non-array type {}", index.layout.ty)
+                };
+                let index_len = index_len.eval_usize(*this.tcx, this.param_env());
+
+                assert_eq!(left_len, right_len);
+                assert_eq!(index_len, dest_len);
+
+                for i in 0..dest_len {
+                    let src_index: u64 = this
+                        .read_immediate(&this.operand_index(&index, i)?.into())?
+                        .to_scalar()?
+                        .to_u32()?
+                        .into();
+                    let dest = this.mplace_index(&dest, i)?;
+
+                    let val = if src_index < left_len {
+                        this.read_immediate(&this.mplace_index(&left, src_index)?.into())?
+                    } else if src_index < left_len.checked_add(right_len).unwrap() {
+                        this.read_immediate(
+                            &this.mplace_index(&right, src_index - left_len)?.into(),
+                        )?
+                    } else {
+                        bug!(
+                            "simd_shuffle index {} is out of bounds for 2 vectors of size {}",
+                            src_index,
+                            left_len
+                        );
+                    };
+                    this.write_immediate(*val, &dest.into())?;
+                }
+            }
 
             // Atomic operations
             "atomic_load" => this.atomic_load(args, dest, AtomicReadOp::SeqCst)?,

tests/run-pass/portable-simd.rs

@@ -238,6 +238,17 @@ fn simd_cast() {
     }
 }
 
+fn simd_swizzle() {
+    use Which::*;
+
+    let a = f32x4::splat(10.0);
+    let b = f32x4::from_array([1.0, 2.0, 3.0, -4.0]);
+
+    assert_eq!(simd_swizzle!(b, [3, 0, 0, 2]), f32x4::from_array([-4.0, 1.0, 1.0, 3.0]));
+    assert_eq!(simd_swizzle!(b, [1, 2]), f32x2::from_array([2.0, 3.0]));
+    assert_eq!(simd_swizzle!(b, a, [First(3), Second(0)]), f32x2::from_array([-4.0, 10.0]));
+}
+
 fn simd_intrinsics() {
     extern "platform-intrinsic" {
         fn simd_eq<T, U>(x: T, y: T) -> U;
@@ -276,5 +287,6 @@ fn main() {
     simd_ops_f64();
     simd_ops_i32();
     simd_cast();
+    simd_swizzle();
     simd_intrinsics();
 }