diff --git a/cranelift/src/libcretonne/types.rs b/cranelift/src/libcretonne/types.rs
index 88a2b6cad2..6c8fb90d90 100644
--- a/cranelift/src/libcretonne/types.rs
+++ b/cranelift/src/libcretonne/types.rs
@@ -3,6 +3,12 @@
 
 use std::fmt::{self, Display, Formatter, Write};
 
+// ====--------------------------------------------------------------------------------------====//
+//
+// Value types
+//
+// ====--------------------------------------------------------------------------------------====//
+
 /// The type of an SSA value.
 ///
 /// The `VOID` type is only used for instructions that produce no value. It can't be part of a SIMD
@@ -177,6 +183,107 @@ impl Display for Type {
     }
 }
 
+// ====--------------------------------------------------------------------------------------====//
+//
+// Function signatures
+//
+// ====--------------------------------------------------------------------------------------====//
+
+/// Function argument extension options.
+///
+/// On some architectures, small integer function arguments are extended to the width of a
+/// general-purpose register.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum ArgumentExtension {
+    /// No extension, high bits are indeterminate.
+    None,
+    /// Unsigned extension: high bits in register are 0.
+    Uext,
+    /// Signed extension: high bits in register replicate sign bit.
+    Sext,
+}
+
+/// Function argument or return value type.
+///
+/// This describes the value type being passed to or from a function along with flags that affect
+/// how the argument is passed.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub struct ArgumentType {
+    pub value_type: Type,
+    pub extension: ArgumentExtension,
+    /// Place this argument in a register if possible.
+    pub inreg: bool,
+}
+
+/// Function signature.
+///
+/// The function signature describes the types of arguments and return values along with other
+/// details that are needed to call a function correctly.
+pub struct Signature {
+    pub argument_types: Vec<ArgumentType>,
+    pub return_types: Vec<ArgumentType>,
+}
+
+impl ArgumentType {
+    pub fn new(vt: Type) -> ArgumentType {
+        ArgumentType {
+            value_type: vt,
+            extension: ArgumentExtension::None,
+            inreg: false,
+        }
+    }
+}
+
+impl Display for ArgumentType {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        try!(write!(f, "{}", self.value_type));
+        match self.extension {
+            ArgumentExtension::None => {}
+            ArgumentExtension::Uext => try!(write!(f, " uext")),
+            ArgumentExtension::Sext => try!(write!(f, " sext")),
+        }
+        if self.inreg {
+            try!(write!(f, " inreg"));
+        }
+        Ok(())
+    }
+}
+
+impl Signature {
+    pub fn new() -> Signature {
+        Signature {
+            argument_types: Vec::new(),
+            return_types: Vec::new(),
+        }
+    }
+}
+
+fn write_list(f: &mut Formatter, args: &Vec<ArgumentType>) -> fmt::Result {
+    match args.split_first() {
+        None => {}
+        Some((first, rest)) => {
+            try!(write!(f, "{}", first));
+            for arg in rest {
+                try!(write!(f, ", {}", arg));
+            }
+        }
+    }
+    Ok(())
+}
+
+impl Display for Signature {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        try!(write!(f, "("));
+        try!(write_list(f, &self.argument_types));
+        try!(write!(f, ")"));
+        if !self.return_types.is_empty() {
+            try!(write!(f, " -> "));
+            try!(write_list(f, &self.return_types));
+        }
+        Ok(())
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -248,4 +355,28 @@ mod tests {
         assert_eq!(format!("{}", I8.by(64)), "i8x64");
         assert_eq!(format!("{}", F64.by(2)), "f64x2");
     }
+
+    #[test]
+    fn argument_type() {
+        let mut t = ArgumentType::new(I32);
+        assert_eq!(format!("{}", t), "i32");
+        t.extension = ArgumentExtension::Uext;
+        assert_eq!(format!("{}", t), "i32 uext");
+        t.inreg = true;
+        assert_eq!(format!("{}", t), "i32 uext inreg");
+    }
+
+    #[test]
+    fn signatures() {
+        let mut sig = Signature::new();
+        assert_eq!(format!("{}", sig), "()");
+        sig.argument_types.push(ArgumentType::new(I32));
+        assert_eq!(format!("{}", sig), "(i32)");
+        sig.return_types.push(ArgumentType::new(F32));
+        assert_eq!(format!("{}", sig), "(i32) -> f32");
+        sig.argument_types.push(ArgumentType::new(I32.by(4)));
+        assert_eq!(format!("{}", sig), "(i32, i32x4) -> f32");
+        sig.return_types.push(ArgumentType::new(B8));
+        assert_eq!(format!("{}", sig), "(i32, i32x4) -> f32, b8");
+    }
 }