refactor[venom]: refactor venom operand classes (#3915)

the original `IRValue`, `IRVariable`, `IRLabel` and `IROperand`
hierarchy got convoluted after several refactors. this commit refactors
the hierarchy so that the relationship between the classes is clearer.

vyper/venom/basicblock.py

@@ -92,8 +92,8 @@ def __repr__(self) -> str:
 
 class IROperand:
     """
-    IROperand represents an operand in IR. An operand is anything that can
-    be an argument to an IRInstruction
+    IROperand represents an IR operand. An operand is anything that can be
+    operated by instructions. It can be a literal, a variable, or a label.
     """
 
     value: Any
@@ -102,18 +102,19 @@ class IROperand:
     def name(self) -> str:
         return self.value
 
+    def __hash__(self) -> int:
+        return hash(self.value)
 
-class IRValue(IROperand):
-    """
-    IRValue represents a value in IR. A value is anything that can be
-    operated by non-control flow instructions. That is, IRValues can be
-    IRVariables or IRLiterals.
-    """
+    def __eq__(self, other) -> bool:
+        if not isinstance(other, type(self)):
+            return False
+        return self.value == other.value
 
-    pass
+    def __repr__(self) -> str:
+        return str(self.value)
 
 
-class IRLiteral(IRValue):
+class IRLiteral(IROperand):
     """
     IRLiteral represents a literal in IR
     """
@@ -124,25 +125,13 @@ def __init__(self, value: int) -> None:
         assert isinstance(value, int), "value must be an int"
         self.value = value
 
-    def __hash__(self) -> int:
-        return self.value.__hash__()
-
-    def __eq__(self, other) -> bool:
-        if not isinstance(other, type(self)):
-            return False
-        return self.value == other.value
-
-    def __repr__(self) -> str:
-        return str(self.value)
-
 
-class IRVariable(IRValue):
+class IRVariable(IROperand):
     """
     IRVariable represents a variable in IR. A variable is a string that starts with a %.
     """
 
     value: str
-    offset: int = 0
 
     def __init__(self, value: str, version: Optional[str | int] = None) -> None:
         assert isinstance(value, str)
@@ -153,7 +142,6 @@ def __init__(self, value: str, version: Optional[str | int] = None) -> None:
         if value[0] != "%":
             value = f"%{value}"
         self.value = value
-        self.offset = 0
 
     @property
     def name(self) -> str:
@@ -165,17 +153,6 @@ def version(self) -> int:
             return 0
         return int(self.value.split(":")[1])
 
-    def __hash__(self) -> int:
-        return self.value.__hash__()
-
-    def __eq__(self, other) -> bool:
-        if not isinstance(other, type(self)):
-            return False
-        return self.value == other.value
-
-    def __repr__(self) -> str:
-        return self.value
-
 
 class IRLabel(IROperand):
     """
@@ -192,16 +169,14 @@ def __init__(self, value: str, is_symbol: bool = False) -> None:
         self.value = value
         self.is_symbol = is_symbol
 
-    def __hash__(self) -> int:
-        return hash(self.value)
+    def __eq__(self, other):
+        # no need for is_symbol to participate in equality
+        return super().__eq__(other)
 
-    def __eq__(self, other) -> bool:
-        if not isinstance(other, type(self)):
-            return False
-        return self.value == other.value
-
-    def __repr__(self) -> str:
-        return self.value
+    def __hash__(self):
+        # __hash__ is required when __eq__ is overridden --
+        # https://docs.python.org/3/reference/datamodel.html#object.__hash__
+        return super().__hash__()
 
 
 class IRInstruction:

vyper/venom/passes/make_ssa.py

@@ -95,7 +95,7 @@ def _rename_vars(self, basic_block: IRBasicBlock):
 
         # Pre-action
         for inst in basic_block.instructions:
-            new_ops = []
+            new_ops: list[IROperand] = []
             if inst.opcode != "phi":
                 for op in inst.operands:
                     if not isinstance(op, IRVariable):
@@ -143,7 +143,7 @@ def _remove_degenerate_phis(self, entry: IRBasicBlock):
             if inst.opcode != "phi":
                 continue
 
-            new_ops = []
+            new_ops: list[IROperand] = []
             for label, op in inst.phi_operands:
                 if op == inst.output:
                     continue