Define a return instruction.

It is possible to return multiple values from a function, so ReturnData contains
a VariableArgs instance.

We don't want return instructions to appear as 'return (v1)', so tweak the
printing of VariableArgs so the parantheses are added externally.

src/libreader/parser.rs

@@ -15,7 +15,7 @@ use cretonne::types::{Type, VOID, FunctionName, Signature, ArgumentType, Argumen
 use cretonne::immediates::{Imm64, Ieee32, Ieee64};
 use cretonne::entities::*;
 use cretonne::instructions::{Opcode, InstructionFormat, InstructionData, VariableArgs, JumpData,
-                             BranchData};
+                             BranchData, ReturnData};
 use cretonne::repr::{Function, StackSlotData};
 
 pub use lexer::Location;
@@ -201,7 +201,11 @@ impl Context {
                 }
 
                 InstructionData::Call { ref mut data, .. } => {
-                    try!(Self::rewrite_values(&self.values, &mut data.arguments, &loc));
+                    try!(Self::rewrite_values(&self.values, &mut data.args, &loc));
+                }
+
+                InstructionData::Return { ref mut data, .. } => {
+                    try!(Self::rewrite_values(&self.values, &mut data.args, &loc));
                 }
             }
         }
@@ -1015,6 +1019,14 @@ impl<'a> Parser<'a> {
                     args: [lhs, rhs],
                 }
             }
+            InstructionFormat::Return => {
+                let args = try!(self.parse_value_list());
+                InstructionData::Return {
+                    opcode: opcode,
+                    ty: VOID,
+                    data: Box::new(ReturnData { args: args }),
+                }
+            }
             InstructionFormat::BranchTable |
             InstructionFormat::Call => {
                 unimplemented!();