Move immediate value retrieval to imm

Copyright (c) 2021, Arm Limited

cranelift/interpreter/src/step.rs

@@ -76,6 +76,16 @@ where
                     .as_slice();
                 DataValue::V128(buffer.try_into().expect("a 16-byte data buffer"))
             }
+            InstructionData::Shuffle { mask, .. } => {
+                let mask = state
+                    .get_current_function()
+                    .dfg
+                    .immediates
+                    .get(mask)
+                    .unwrap()
+                    .as_slice();
+                DataValue::V128(mask.try_into().expect("a 16-byte vector mask"))
+            }
             _ => inst.imm_value().unwrap(),
         })
     };
@@ -777,14 +787,7 @@ where
             ValueConversionKind::RoundNearestEven(ctrl_ty),
         )?),
         Opcode::Shuffle => {
-            if let InstructionData::Shuffle { mask, .. } = inst {
+            let mask = imm().into_array()?;
-                let mask = state
-                    .get_current_function()
-                    .dfg
-                    .immediates
-                    .get(mask)
-                    .unwrap()
-                    .as_slice();
             let a = Value::into_array(&arg(0)?)?;
             let b = Value::into_array(&arg(1)?)?;
             let mut new = [0u8; 16];
@@ -796,9 +799,6 @@ where
                 } // else leave as 0.
             }
             assign(Value::vector(new, ctrl_ty)?)
-            } else {
-                unreachable!();
-            }
         }
         Opcode::Swizzle => {
             let x = Value::into_array(&arg(0)?)?;