Generate type numbers at meta-time.

We need to generate hash tables keyed by types, so the Python scripts need to
know the index used to represent types in Rust code.

To enforce this, add a new gen_types.py script which generates constant
definitions for the ir/types module.

Also generate constants for common SIMD vector sizes.

meta/gen_types.py

@@ -0,0 +1,51 @@
+"""
+Generate sources with type info.
+
+This generates a `types.rs` file which is included in
+`libcretonne/ir/types/rs`. The file provides constant definitions for the most
+commonly used types, including all of the scalar types.
+
+This ensures that Python and Rust use the same type numbering.
+"""
+from __future__ import absolute_import
+import srcgen
+from cretonne import ValueType
+
+
+def emit_type(ty, fmt):
+    """
+    Emit a constant definition of a single value type.
+    """
+    name = ty.name.upper()
+    fmt.doc_comment(ty.__doc__)
+    fmt.line(
+            'pub const {}: Type = Type({:#x});'
+            .format(name, ty.number))
+
+
+def emit_vectors(bits, fmt):
+    """
+    Emit definition for all vector types with `bits` total size.
+    """
+    size = bits // 8
+    for ty in ValueType.all_scalars:
+        mb = ty.membytes
+        if mb == 0 or mb >= size:
+            continue
+        emit_type(ty.by(size // mb), fmt)
+
+
+def emit_types(fmt):
+    for ty in ValueType.all_scalars:
+        emit_type(ty, fmt)
+    # Emit vector definitions for common SIMD sizes.
+    emit_vectors(64, fmt)
+    emit_vectors(128, fmt)
+    emit_vectors(256, fmt)
+    emit_vectors(512, fmt)
+
+
+def generate(out_dir):
+    fmt = srcgen.Formatter()
+    emit_types(fmt)
+    fmt.update_file('types.rs', out_dir)