fix[venom]: add unique_symbols check to venom pipeline (#4149)

when `-Onone` is specified along with `--experimental-codegen`,
the unique symbols check does not get run. this calculates the
`ir_node.unique_symbols` property, which implicitly runs the unique
symbols check.

also, change an assertion to a proper panic exception

vyper/codegen/ir_node.py

@@ -405,7 +405,8 @@ def unique_symbols(self):
         for arg in children:
             s = arg.unique_symbols
             non_uniques = ret.intersection(s)
-            assert len(non_uniques) == 0, f"non-unique symbols {non_uniques}"
+            if len(non_uniques) != 0:  # pragma: nocover
+                raise CompilerPanic(f"non-unique symbols {non_uniques}")
             ret |= s
         return ret
 

vyper/venom/ir_node_to_venom.py

@@ -114,6 +114,8 @@
 
 # convert IRnode directly to venom
 def ir_node_to_venom(ir: IRnode) -> IRContext:
+    _ = ir.unique_symbols  # run unique symbols check
+
     global _global_symbols, _external_functions
     _global_symbols = {}
     _external_functions = {}