Add a TypeDocumenter for Cretonne types.

Use the autodoc Sphinx module to add a .. autoctontype:: directive which
generates documentation for one of the types in the cretonne.types module.

meta/cretonne/__init__.py

@@ -12,6 +12,11 @@ instructions.
 class Type(object):
     """A concrete value type."""
 
+    def __init__(self, name, membytes, doc):
+        self.name = name
+        self.membytes = membytes
+        self.__doc__ = doc
+
     def __str__(self):
         return self.name
 
@@ -19,12 +24,12 @@ class ScalarType(Type):
     """
     A concrete scalar (not vector) type.
 
-    Also tracks a unique set of :class:`VectorType` instances with this type as
-    the lane type.
+    Also tracks a unique set of :py:class:`VectorType` instances with this type
+    as the lane type.
     """
 
-    def __init__(self, name):
-        self.name = name
+    def __init__(self, name, membytes, doc):
+        super(ScalarType, self).__init__(name, membytes, doc)
         self._vectors = dict()
 
     def __repr__(self):
@@ -53,9 +58,14 @@ class VectorType(Type):
 
     def __init__(self, base, lanes):
         assert isinstance(base, ScalarType), 'SIMD lanes must be scalar types'
+        super(VectorType, self).__init__(
+                name='{}x{}'.format(base.name, lanes),
+                membytes=lanes*base.membytes,
+                doc="""
+                A SIMD vector with {} lanes containing a {} each.
+                """.format(lanes, base.name))
         self.base = base
         self.lanes = lanes
-        self.name = '{}x{}'.format(base.name, lanes)
 
     def __repr__(self):
         return 'VectorType(base={}, lanes={})'.format(self.base.name, self.lanes)
@@ -65,7 +75,10 @@ class IntType(ScalarType):
 
     def __init__(self, bits):
         assert bits > 0, 'IntType must have positive number of bits'
-        super(IntType, self).__init__('i{:d}'.format(bits))
+        super(IntType, self).__init__(
+                name='i{:d}'.format(bits),
+                membytes=bits/8,
+                doc="An integer type with {} bits.".format(bits))
         self.bits = bits
 
     def __repr__(self):
@@ -74,9 +87,9 @@ class IntType(ScalarType):
 class FloatType(ScalarType):
     """A concrete scalar floating point type."""
 
-    def __init__(self, bits):
+    def __init__(self, bits, doc):
         assert bits > 0, 'FloatType must have positive number of bits'
-        super(FloatType, self).__init__('f{:d}'.format(bits))
+        super(FloatType, self).__init__( name='f{:d}'.format(bits), membytes=bits/8, doc=doc)
         self.bits = bits
 
     def __repr__(self):

meta/cretonne/types.py

@@ -2,19 +2,32 @@
 
 from . import ScalarType, IntType, FloatType
 
-#: A boolean value.
-bool = ScalarType('bool')
+bool = ScalarType('bool', 0,
+        """
+        A boolean value that is either true or false.
+        """)
 
-i8  = IntType(8)  #: 8-bit int.
-i16 = IntType(16) #: 16-bit int.
-i32 = IntType(32) #: 32-bit int.
-i64 = IntType(64) #: 64-bit int.
+i8  = IntType(8)
+i16 = IntType(16)
+i32 = IntType(32)
+i64 = IntType(64)
 
-f32 = FloatType(32) #: IEEE 32-bit float.
-f64 = FloatType(64) #: IEEE 64-bit float
+f32 = FloatType(32,
+        """
+        A 32-bit floating point type represented in the IEEE 754-2008 *binary32*
+        interchange format. This corresponds to the :c:type:`float` type in most
+        C implementations.
+        """)
 
-i8x16 = i8.by(16) #: Vector of 16 i8 lanes.
+f64 = FloatType(64,
+        """
+        A 64-bit floating point type represented in the IEEE 754-2008 *binary64*
+        interchange format. This corresponds to the :c:type:`double` type in
+        most C implementations.
+        """)
 
-f32x4 = f32.by(4) #: Vector of 4 f32 lanes.
-f64x2 = f64.by(2) #: Vector of 2 f64 lanes.
+i8x16 = i8.by(16)
+
+f32x4 = f32.by(4)
+f64x2 = f64.by(2)