[PyCDE] Clarify BackedgeBuilder error message

Presumably, this error message stems from when BackedgeBuilder was initially used solely for creating backedges to top-level port assignments when creating a new module instance. However, the `BackedgeBuilder` is also used for other operations (and useful as a general tool), wherein 'port' may be misleading. Changing this to `Backedge` makes it explicit that a backedge was created, and was expected to be assigned to.

integration_test/Bindings/Python/dialects/rtl_errors.py

@@ -59,8 +59,8 @@ with Context() as ctx, Location.unknown():
         print(e)
 
       # Note, the error here is actually caught and printed below.
-      # CHECK: Uninitialized ports remain in circuit!
-      # CHECK: Port:       [[PORT_NAME:.+]]
+      # CHECK: Uninitialized backedges remain in circuit!
+      # CHECK: Backedge:   [[PORT_NAME:.+]]
       # CHECK: InstanceOf: hw.module @one_input(%[[PORT_NAME]]: i32)
       # CHECK: Instance:   hw.instance "inst1" @one_input({{.+}})
       inst1 = one_input.instantiate("inst1")

lib/Bindings/Python/circt/support.py

@@ -178,7 +178,7 @@ class BackedgeBuilder(AbstractContextManager):
     def __init__(self,
                  creator,
                  type: ir.Type,
-                 port_name: str,
+                 backedge_name: str,
                  op_view,
                  instance_of: ir.Operation,
                  loc: ir.Location = None):
@@ -186,7 +186,7 @@ class BackedgeBuilder(AbstractContextManager):
       self.dummy_op = ir.Operation.create("TemporaryBackedge", [type], loc=loc)
       self.instance_of = instance_of
       self.op_view = op_view
-      self.port_name = port_name
+      self.port_name = backedge_name
       self.erased = False
 
     @property
@@ -236,7 +236,7 @@ class BackedgeBuilder(AbstractContextManager):
     errors = []
     for edge in list(self.edges):
       # TODO: Make this use `UnconnectedSignalError`.
-      msg = "Port:       " + edge.port_name + "\n"
+      msg = "Backedge:   " + edge.port_name + "\n"
       if edge.instance_of is not None:
         msg += "InstanceOf: " + str(edge.instance_of).split(" {")[0] + "\n"
       if edge.op_view is not None:
@@ -245,7 +245,7 @@ class BackedgeBuilder(AbstractContextManager):
       errors.append(msg)
 
     if errors:
-      errors.insert(0, "Uninitialized ports remain in circuit!")
+      errors.insert(0, "Uninitialized backedges remain in circuit!")
       raise RuntimeError("\n".join(errors))