diff --git a/cranelift/src/libcretonne/immediates.rs b/cranelift/src/libcretonne/immediates.rs
index efd84cd606..0034139f50 100644
--- a/cranelift/src/libcretonne/immediates.rs
+++ b/cranelift/src/libcretonne/immediates.rs
@@ -8,6 +8,9 @@
 use std::fmt::{self, Display, Formatter};
 use std::mem;
 
+// The `Opcode` enum is generated from the meta instruction descriptions.
+include!(concat!(env!("OUT_DIR"), "/opcodes.rs"));
+
 /// 64-bit immediate integer operand.
 ///
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
@@ -41,11 +44,13 @@ impl Display for Imm64 {
 /// An IEEE binary32 immediate floating point value.
 ///
 /// All bit patterns are allowed.
+#[derive(Copy, Clone, Debug)]
 pub struct Ieee32(f32);
 
 /// An IEEE binary64 immediate floating point value.
 ///
 /// All bit patterns are allowed.
+#[derive(Copy, Clone, Debug)]
 pub struct Ieee64(f64);
 
 // Format a floating point number in a way that is reasonably human-readable, and that can be
@@ -155,6 +160,19 @@ mod tests {
     use super::*;
     use std::{f32, f64};
 
+    #[test]
+    fn opcodes() {
+        let x = Opcode::Iadd;
+        let mut y = Opcode::Isub;
+
+        assert!(x != y);
+        y = Opcode::Iadd;
+        assert_eq!(x, y);
+
+        assert_eq!(format!("{:?}", Opcode::IaddImm), "IaddImm");
+        assert_eq!(format!("{}", Opcode::IaddImm), "iadd_imm");
+    }
+
     #[test]
     fn format_imm64() {
         assert_eq!(format!("{}", Imm64(0)), "0");
diff --git a/meta/gen_instr.py b/meta/gen_instr.py
index a92609c861..cd50b4ee8a 100644
--- a/meta/gen_instr.py
+++ b/meta/gen_instr.py
@@ -17,13 +17,31 @@ def collect_instr_groups(targets):
 def gen_opcodes(groups, out_dir):
     """Generate opcode enumerations."""
     fmt = srcgen.Formatter()
-    fmt.line('enum Opcode {')
-    fmt.indent_push()
-    for g in groups:
-        for i in g.instructions:
-            fmt.line(i.camel_name + ',')
-    fmt.indent_pop()
-    fmt.line('}')
+
+    fmt.doc_comment('An instruction opcode.')
+    fmt.doc_comment('')
+    fmt.doc_comment('All instructions from all supported targets are present.')
+    fmt.line('#[derive(Copy, Clone, PartialEq, Eq, Debug)]')
+    instrs = []
+    with fmt.indented('pub enum Opcode {', '}'):
+        for g in groups:
+            for i in g.instructions:
+                instrs.append(i)
+                # Build a doc comment.
+                prefix = ', '.join(o.name for o in i.outs)
+                if prefix:
+                    prefix = prefix + ' = '
+                suffix = ', '.join(o.name for o in i.ins)
+                fmt.doc_comment('`{}{} {}`.'.format(prefix, i.name, suffix))
+                # Enum variant itself.
+                fmt.line(i.camel_name + ',')
+
+    with fmt.indented('impl Display for Opcode {', '}'):
+        with fmt.indented('fn fmt(&self, f: &mut Formatter) -> fmt::Result {', '}'):
+            with fmt.indented('f.write_str(match *self {', '})'):
+                for i in instrs:
+                    fmt.format('Opcode::{} => "{}",', i.camel_name, i.name)
+
     fmt.update_file('opcodes.rs', out_dir)
 
 def generate(targets, out_dir):
diff --git a/meta/srcgen.py b/meta/srcgen.py
index 9778e2c518..125ae0a63a 100644
--- a/meta/srcgen.py
+++ b/meta/srcgen.py
@@ -25,15 +25,15 @@ class Formatter(object):
         >>> f.indent_push()
         >>> f.comment('Nested comment')
         >>> f.indent_pop()
-        >>> f.line('Back again')
+        >>> f.format('Back {} again', 'home')
         >>> f.writelines()
         Hello line 1
-          // Nested comment
-        Back again
+            // Nested comment
+        Back home again
 
     """
 
-    shiftwidth = 2
+    shiftwidth = 4
 
     def __init__(self):
         self.indent = ''
@@ -64,10 +64,49 @@ class Formatter(object):
         with open(filename, 'w') as f:
             self.writelines(f)
 
+    class _IndentedScope(object):
+        def __init__(self, fmt, after):
+            self.fmt = fmt
+            self.after = after
+
+        def __enter__(self):
+            self.fmt.indent_push();
+
+        def __exit__(self, t, v, tb):
+            self.fmt.indent_pop()
+            if self.after:
+                self.fmt.line(self.after)
+
+    def indented(self, before=None, after=None):
+        """
+        Return a scope object for use with a `with` statement:
+
+            >>> f = Formatter()
+            >>> with f.indented('prefix {', '} suffix'):
+            ...     f.line('hello')
+            >>> f.writelines()
+            prefix {
+                hello
+            } suffix
+
+        The optional `before` and `after` parameters are surrounding lines
+        which are *not* indented.
+        """
+        if before:
+            self.line(before)
+        return self._IndentedScope(self, after)
+
+    def format(self, fmt, *args):
+        self.line(fmt.format(*args))
+
     def comment(self, s):
         """Add a comment line."""
         self.line('// ' + s)
 
+    def doc_comment(self, s):
+        """Add a documentation comment line."""
+        self.line('/// ' + s)
+
 if __name__ == "__main__":
     import doctest
     doctest.testmod()