Implement Swizzle and Splat for interpreter (#3268)

* Implement `Swizzle` and `Splat` for interpreter

Implemented for the Cranelift interpreter:
- `Swizzle` to shuffle an `i8x16` SIMD vector based
on the indices specified in another vector of the same size.
- `Splat` to create a SIMD vector with all lanes having the same value.

Copyright (c) 2021, Arm Limited

* Fix old x86 backend failing test

Copyright (c) 2021, Arm Limited

* Represent i16x8 and above as hex

Copyright (c) 2021, Arm Limited

cranelift/filetests/filetests/runtests/simd-splat.clif

@@ -0,0 +1,33 @@
+test interpret
+test run
+target aarch64
+set enable_simd
+target x86_64
+
+function %splat_i8x16(i8) -> i8x16 {
+block0(v0: i8):
+    v1 = splat.i8x16 v0
+    return v1
+}
+; run: %splat_i8x16(1) == [1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1]
+
+function %splat_i16x8(i16) -> i16x8 {
+block0(v0: i16):
+    v1 = splat.i16x8 v0
+    return v1
+}
+; run: %splat_i16x8(512) == [512 512 512 512 512 512 512 512]
+
+function %splat_i32x4(i32) -> i32x4 {
+block0(v0: i32):
+    v1 = splat.i32x4 v0
+    return v1
+}
+; run: %splat_i32x4(2000000) == [2000000 2000000 2000000 2000000]
+
+function %splat_i64x2(i64) -> i64x2 {
+block0(v0: i64):
+    v1 = splat.i64x2 v0
+    return v1
+}
+; run: %splat_i64x2(5000000000) == [5000000000 5000000000]

cranelift/filetests/filetests/runtests/simd-swizzle.clif

@@ -0,0 +1,33 @@
+test interpret
+test run
+target aarch64
+set enable_simd
+target x86_64 machinst
+
+function %swizzle_i8x16(i8x16, i8x16) -> i8x16 {
+block0(v0: i8x16, v1: i8x16):
+    v2 = swizzle.i8x16 v0, v1
+    return v2
+}
+; run: %swizzle_i8x16([1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16], [0 9 15 1 6 13 7 11 10 8 100 12 4 2 3 5]) == [1 10 16 2 7 14 8 12 11 9 0 13 5 3 4 6]
+
+function %swizzle_i16x8(i8x16, i8x16) -> i16x8 {
+block0(v0: i8x16, v1: i8x16):
+    v2 = swizzle.i16x8 v0, v1
+    return v2
+}
+; run: %swizzle_i16x8([1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16], [0 9 15 1 6 13 7 11 10 8 100 12 4 2 3 5]) == 0x060403050d00090b0c080e0702100a01
+
+function %swizzle_i32x4(i8x16, i8x16) -> i32x4 {
+block0(v0: i8x16, v1: i8x16):
+    v2 = swizzle.i32x4 v0, v1
+    return v2
+}
+; run: %swizzle_i32x4([1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16], [0 9 15 1 6 13 7 11 10 8 100 12 4 2 3 5]) == 0x060403050d00090b0c080e0702100a01
+
+function %swizzle_i64x2(i8x16, i8x16) -> i64x2 {
+block0(v0: i8x16, v1: i8x16):
+    v2 = swizzle.i64x2 v0, v1
+    return v2
+}
+; run: %swizzle_i64x2([1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16], [0 9 15 1 6 13 7 11 10 8 100 12 4 2 3 5]) == 0x060403050d00090b0c080e0702100a01

cranelift/interpreter/src/step.rs

@@ -777,8 +777,24 @@ where
             ValueConversionKind::RoundNearestEven(ctrl_ty),
         )?),
         Opcode::Shuffle => unimplemented!("Shuffle"),
-        Opcode::Swizzle => unimplemented!("Swizzle"),
+        Opcode::Swizzle => {
-        Opcode::Splat => unimplemented!("Splat"),
+            let x = Value::into_array(&arg(0)?)?;
+            let s = Value::into_array(&arg(1)?)?;
+            let mut new = [0u8; 16];
+            for i in 0..new.len() {
+                if (s[i] as usize) < new.len() {
+                    new[i] = x[s[i] as usize];
+                } // else leave as 0
+            }
+            assign(Value::vector(new, ctrl_ty)?)
+        }
+        Opcode::Splat => {
+            let mut new_vector = SimdVec::new();
+            for _ in 0..ctrl_ty.lane_count() {
+                new_vector.push(arg(0)?.into_int()?);
+            }
+            assign(vectorizelanes(&new_vector, ctrl_ty)?)
+        }
         Opcode::Insertlane => {
             let idx = imm().into_int()? as usize;
             let mut vector = extractlanes(&arg(0)?, ctrl_ty.lane_type())?;