build/xilinx/vivado: Allow passing str to add_false_path_constraint to allow mising Signals and str and simplify design constraints.

litex/build/xilinx/vivado.py

@@ -217,13 +217,26 @@ class XilinxVivadoToolchain(GenericToolchain):
                 False: "nets",
                 True: "ports",
             }[hasattr(clk, "port")]
-        for _from, _to in sorted(self.false_paths, key=lambda x: (x[0].duid, x[1].duid)):
+
+        for _from, _to in sorted(self.false_paths, key=lambda x: (str(x[0]), str(x[1]))):
+            if isinstance(_from, str):
+                _from_cmd = f"[get_clocks {_from}]"
+            else:
+                _from_cmd = f"[get_clocks -include_generated_clocks -of [get_{get_clk_type(_from)} {{_from}}]]"
+
+            if isinstance(_to, str):
+                _to_cmd = f"[get_clocks {_to}]"
+            else:
+                _to_cmd = f"[get_clocks -include_generated_clocks -of [get_{get_clk_type(_to)} {{_to}}]]"
+
             self.platform.add_platform_command(
                 "set_clock_groups "
-                "-group [get_clocks -include_generated_clocks -of [get_" + get_clk_type(_from) + " {_from}]] "
+                f"-group {_from_cmd} "
-                "-group [get_clocks -include_generated_clocks -of [get_" + get_clk_type(_to)   + " {_to}]] "
+                f"-group {_to_cmd} "
                 "-asynchronous",
-                _from=_from, _to=_to)
+                _from = _from if not isinstance(_from, str) else None,
+                _to   = _to   if not isinstance(_to, str)   else None,
+            )
 
         # Clear false path constraints after generation.
         self.false_paths.clear()