back.{rtlil,verilog}: split convert_fragment() off convert().

Because Fragment.prepare is not (currently) idempotent, it is useful
to be able to avoid calling it when converting. Even if it is made
idempotent, it can be slow on large designs, so it is advantageous
regardless of that.

nmigen/back/rtlil.py

@@ -7,7 +7,7 @@ from ..tools import bits_for, flatten
 from ..hdl import ast, rec, ir, mem, xfrm
 
 
-__all__ = ["convert"]
+__all__ = ["convert", "convert_fragment"]
 
 
 class _Namer:
@@ -720,7 +720,7 @@ class _StatementCompiler(xfrm.StatementVisitor):
             self.on_statement(stmt)
 
 
-def convert_fragment(builder, fragment, hierarchy):
+def _convert_fragment(builder, fragment, hierarchy):
     if isinstance(fragment, ir.Instance):
         port_map = OrderedDict()
         for port_name, (value, dir) in fragment.named_ports.items():
@@ -807,7 +807,7 @@ def convert_fragment(builder, fragment, hierarchy):
                     sub_params[param_name] = param_value
 
             sub_type, sub_port_map = \
-                convert_fragment(builder, subfragment, hierarchy=hierarchy + (sub_name,))
+                _convert_fragment(builder, subfragment, hierarchy=hierarchy + (sub_name,))
 
             sub_ports = OrderedDict()
             for port, value in sub_port_map.items():
@@ -938,8 +938,13 @@ def convert_fragment(builder, fragment, hierarchy):
     return module.name, port_map
 
 
-def convert(fragment, name="top", platform=None, **kwargs):
+def convert_fragment(fragment, name="top"):
-    fragment = ir.Fragment.get(fragment, platform).prepare(**kwargs)
+    assert isinstance(fragment, ir.Fragment)
     builder = _Builder()
-    convert_fragment(builder, fragment, hierarchy=(name,))
+    _convert_fragment(builder, fragment, hierarchy=(name,))
     return str(builder)
+
+
+def convert(elaboratable, name="top", platform=None, **kwargs):
+    fragment = ir.Fragment.get(elaboratable, platform).prepare(**kwargs)
+    return convert_fragment(fragment, name)

nmigen/back/verilog.py

@@ -4,14 +4,14 @@ import subprocess
 from . import rtlil
 
 
-__all__ = ["convert"]
+__all__ = ["YosysError", "convert", "convert_fragment"]
 
 
 class YosysError(Exception):
     pass
 
 
-def convert(*args, strip_src=False, **kwargs):
+def _convert_il_text(il_text, strip_src):
     try:
         popen = subprocess.Popen([os.getenv("YOSYS", "yosys"), "-q", "-"],
             stdin=subprocess.PIPE,
@@ -30,7 +30,6 @@ def convert(*args, strip_src=False, **kwargs):
     if strip_src:
         attr_map.append("-remove src")
 
-    il_text = rtlil.convert(*args, **kwargs)
     verilog_text, error = popen.communicate("""
 # Convert nMigen's RTLIL to readable Verilog.
 read_ilang <<rtlil
@@ -49,3 +48,13 @@ write_verilog -norename
         raise YosysError(error.strip())
     else:
         return verilog_text
+
+
+def convert_fragment(*args, strip_src=False, **kwargs):
+    il_text = rtlil.convert_fragment(*args, **kwargs)
+    return _convert_il_text(il_text, strip_src)
+
+
+def convert(*args, strip_src=False, **kwargs):
+    il_text = rtlil.convert(*args, **kwargs)
+    return _convert_il_text(il_text, strip_src)

nmigen/compat/fhdl/verilog.py

@@ -21,7 +21,7 @@ def convert(fi, ios=None, name="top", special_overrides=dict(),
         if create_clock_domains:
             return ClockDomain(name)
     v_output = verilog.convert(
-        fragment=Fragment.get(fi.get_fragment(), platform=None),
+        elaboratable=fi.get_fragment(),
         name=name,
         ports=ios or (),
         missing_domain=missing_domain