Add compiler improvement

Project-02-03-04-05/optimizations/DeadAssignmentElimination.py

@@ -0,0 +1,46 @@
+from __future__ import annotations
+
+import cfg_build
+from cfg.CFG import CFG
+from cfg.CFG_Node import CFG_Node
+from cfa.ReachedUses import ReachedUses
+from syntax import EXPRESSION, ASSIGN
+from optimizations.Optimization import Optimization
+
+class DeadAssignmentElimination(Optimization):
+    def __init__(self) -> None:
+        self._node_by_ast_id: dict[int, CFG_Node] = {}
+        self.__ru: ReachedUses | None = None
+
+    def setup(self, ast: EXPRESSION) -> None:
+        cfg_build.FUNCTIONS.clear()
+        cfg_build.CURRENT_FUNCTION = None
+        cfg = CFG(ast)
+        self.__ru = ReachedUses(cfg)
+        self._node_by_ast_id = {id(n.ast_node): n for n in self.__ru.cfg.nodes() if n.ast_node is not None}
+
+    def apply(self, node: EXPRESSION) -> EXPRESSION:
+        # Only ASSIGN nodes can be dead assignments.
+        if not isinstance(node, ASSIGN):
+            return node
+
+        # Find the CFG node corresponding to this AST node.
+        # If none is found, the node was not analyzed — leave it unchanged.
+        cfg_node = self._node_by_ast_id.get(id(node))
+        if cfg_node is None:
+            return node
+
+        ru = self.__ru
+        nid = cfg_node.id
+        defined_vars = ru.defs.get(nid, set())
+        out = ru.out_sets.get(nid, set())
+
+        # Check if any use-fact in OUT(n) belongs to a variable defined at n.
+        # If so, the assignment is live — at least one use is reachable from here.
+        for (_, var) in out:
+            if var in defined_vars:
+                return node
+
+        # No reached use found for the assigned variable — the assignment is dead.
+        # Replace ASSIGN(var, expr) with expr to preserve side effects on the RHS.
+        return node.expr