implement simd_select

Author: RalfJung

rust-version

@@ -1 +1 @@
-6a705566166debf5eff88c57140df607fa409aaa
+f0c4da49983aa699f715caf681e3154b445fb60b

src/shims/intrinsics.rs

@@ -386,6 +386,28 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
                 this.write_scalar(Scalar::from_bool(res), dest)?;
             }
+            "simd_select" => {
+                let &[ref mask, ref yes, ref no] = check_arg_count(args)?;
+                let (mask, mask_len) = this.operand_to_simd(mask)?;
+                let (yes, yes_len) = this.operand_to_simd(yes)?;
+                let (no, no_len) = this.operand_to_simd(no)?;
+                let (dest, dest_len) = this.place_to_simd(dest)?;
+
+                assert_eq!(dest_len, mask_len);
+                assert_eq!(dest_len, yes_len);
+                assert_eq!(dest_len, no_len);
+
+                for i in 0..dest_len {
+                    let mask = this.read_immediate(&this.mplace_index(&mask, i)?.into())?;
+                    let yes = this.read_immediate(&this.mplace_index(&yes, i)?.into())?;
+                    let no = this.read_immediate(&this.mplace_index(&no, i)?.into())?;
+                    let dest = this.mplace_index(&dest, i)?;
+
+                    let mask = simd_element_to_bool(mask)?;
+                    let val = if mask { yes } else { no };
+                    this.write_immediate(*val, &dest.into())?;
+                }
+            }
 
             // Atomic operations
             "atomic_load" => this.atomic_load(args, dest, AtomicReadOp::SeqCst)?,

tests/run-pass/portable-simd.rs

@@ -29,19 +29,22 @@ fn simd_ops_i32() {
 
 fn simd_intrinsics() {
     extern "platform-intrinsic" {
-        pub(crate) fn simd_eq<T, U>(x: T, y: T) -> U;
-        pub(crate) fn simd_reduce_any<T>(x: T) -> bool;
+        fn simd_eq<T, U>(x: T, y: T) -> U;
+        fn simd_reduce_any<T>(x: T) -> bool;
+        fn simd_select<M, T>(m: M, yes: T, no: T) -> T;
     }
-
-    // Make sure simd_eq returns all-1 for `true`
-    let a = i32x4::splat(10);
-    let b = i32x4::from_array([1, 2, 10, 4]);
-    let c: i32x4 = unsafe { simd_eq(a, b) };
-    assert_eq!(c, i32x4::from_array([0, 0, -1, 0]));
-
     unsafe {
+        // Make sure simd_eq returns all-1 for `true`
+        let a = i32x4::splat(10);
+        let b = i32x4::from_array([1, 2, 10, 4]);
+        let c: i32x4 = simd_eq(a, b);
+        assert_eq!(c, i32x4::from_array([0, 0, -1, 0]));
+
         assert!(!simd_reduce_any(i32x4::splat(0)));
         assert!(simd_reduce_any(i32x4::splat(-1)));
+
+        assert_eq!(simd_select(i8x4::from_array([0, -1, -1, 0]), a, b), i32x4::from_array([1, 10, 10, 4]));
+        assert_eq!(simd_select(i8x4::from_array([0, -1, -1, 0]), b, a), i32x4::from_array([10, 2, 10, 10]));
     }
 }