feat: Type checker for Analog frontend

docs/frontend/analog_frontend.md

@@ -1,4 +1,4 @@
-The analog frontend provides tools to convert analog source text into a parsed tree and to convert a parsed tree back into source text.
+The analog frontend provides tools to convert analog source text into a typed Abstract Syntax Tree (AST) and to convert a typed AST back into source text.
 
 ## Frontend Components
 
@@ -21,7 +21,7 @@ For more details on the analog grammar, see [`analog_grammar.md`](../grammar/ana
 
 ### AST Builder
 
-[`AnalogCircuitAST.py`](../../src/oqd_core/frontend/analog/AnalogCircuitAST.py) contains the implementation of the AST Builder. The `parse_analog` function uses the `AnalogASTBuilder` class to convert the analog source text into an [`AnalogCircuit`][oqd_core.interface.analog.circuit.AnalogCircuit].
+[`AnalogCircuitAST.py`](../../src/oqd_core/frontend/analog/AnalogCircuitAST.py) contains the implementation of the AST Builder. The `parse_analog` function uses the `AnalogASTBuilder` class to convert the analog source text into an [`AnalogCircuit`][oqd_core.interface.analog.circuit.AnalogCircuit]. It produces a typed AST of the source code.
 
 ### Serializer
 
@@ -65,3 +65,12 @@ serialized = serialize_analog(circuit)
 ```
 
 ///
+
+### Type Checker
+
+The analog type checker is implemented by the `AnalogTypeChecker` class in [`type_checker.py`](../../src/oqd_core/frontend/analog/type_checker.py). The `AnalogTypeLattice` class defines a concrete lattice for analog types with `leq`, `join`, and `meet` methods. The type checker builds a Control Flow Graph (CFG) using methods from `cfg.py` from the typed AST, and runs the forward dataflow analysis on the CFG.
+
+### Control Flow Graph
+
+The analog Control Flow Graph (CFG) is implemented by the `CFGNode` and `AnalogCFGBuilder` classes in [`cfg.py`](../../src/oqd_core/frontend/analog/cfg.py). This script also implements an infinite loop checker by identifying strongly connected components (SCCs) in the CFG.
+

examples/analog/test.analog

@@ -25,9 +25,9 @@ I = %I
 C = %C
 A = %A
 J = %J
-H_single = 0.5 * %X + 0.5 * %Z
+H_single = 0.5 %* %X %+ 0.5 %* %Z
 H_pair = (%X %@ %I) %+ (%I %@ %X)
-H_rabi = (0.5 * #t) * (%X %@ %I) %+ 0.5 * (%I %@ %Y)
+H_rabi = (0.5 * #t) %* (%X %@ %I) %+ 0.5 %* (%I %@ %Y)
 
 //control flow
 x = 1
@@ -69,7 +69,7 @@ initialize(r)
 // evolve(hamiltonian, duration, target)
 evolve(H_single, 2.0, r)
 evolve(H_pair, 1.0, targets)
-evolve(%X * 0.5, pi, q0)
+evolve(%X %* 0.5, pi, q0)
 
 measure(r)
 measurement = measure(q0)

src/oqd_core/analysis/__init__.py

@@ -0,0 +1,7 @@
+from .utils import CFGNode, SCCAnalysis
+
+########################################################################################
+__all__ = [
+    "CFGNode",
+    "SCCAnalysis",
+]

src/oqd_core/analysis/utils.py

@@ -0,0 +1,151 @@
+# Copyright 2024-2025 Open Quantum Design
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+
+class CFGNode:
+    def __init__(self, register_id, stmt,  preds = None, kind = "stmt"):
+        self.register_id = register_id
+        self.stmt = stmt
+        self.preds = list(preds) if preds is not None else []
+        self.succs = []
+        self.kind = kind
+        self.exit_nodes = []
+        self.edge_labels = {}
+
+    def add_succ(self, succ, label=None):
+        if succ not in self.succs:
+            self.succs.append(succ)
+        if label is not None:
+            self.edge_labels[succ.register_id] = label
+
+    def add_pred(self, pred, label=None):
+        if pred not in self.preds:
+            self.preds.append(pred)
+        pred.add_succ(self, label=label)
+
+    def add_preds(self, preds, label=None):
+        for pred in preds:
+            self.add_pred(pred, label=label)
+
+    def to_dict(self):
+        if isinstance(self.stmt, str):
+            stmt_repr = self.stmt
+        elif hasattr(self.stmt, "class_"):
+            stmt_repr = self.stmt.class_
+        else:
+            stmt_repr = type(self.stmt).__name__
+        return {
+            "id": self.register_id,
+            "kind": self.kind,
+            "stmt": stmt_repr,
+            "preds": [p.register_id for p in self.preds],
+            "succs": [c.register_id for c in self.succs],
+            "edges": [
+                {"to": c.register_id, "label": self.edge_labels.get(c.register_id)}
+                for c in self.succs
+            ],
+            "exit_nodes": [n.register_id for n in self.exit_nodes],
+        }
+
+
+
+
+class SCCAnalysis:
+    def __init__(self, cfg):
+        self.cfg = cfg
+        self.time = 0
+        self.disc = {nid: -1 for nid in cfg}
+        self.low = {nid: -1 for nid in cfg}
+        self.on_stack = {nid: False for nid in cfg}
+        self.stack = []
+        self.sccs = []
+
+    def dfs(self, u):
+        self.disc[u] = self.time
+        self.low[u] = self.time
+        self.time += 1
+        self.stack.append(u)
+        self.on_stack[u] = True
+        for succ in self.cfg[u].succs:
+            v = succ.register_id
+            if self.disc[v] == -1:
+                self.dfs(v)
+                self.low[u] = min(self.low[u], self.low[v])
+            elif self.on_stack[v]:
+                self.low[u] = min(self.low[u], self.disc[v])
+        if self.low[u] == self.disc[u]:
+            comp = set()
+            while True:
+                w = self.stack.pop()
+                self.on_stack[w] = False
+                comp.add(w)
+                if w == u:
+                    break
+            self.sccs.append(comp)
+
+    def run(self):
+        for nid in self.cfg:
+            if self.disc[nid] == -1:
+                self.dfs(nid)
+        return self.sccs
+
+    def edge_feasible(self, src, dst_id):
+        if src.kind == "branch":
+            label = src.edge_labels.get(dst_id)
+            if src.stmt.value is True and label == "false":
+                return False
+            if src.stmt.value is False and label == "true":
+                return False
+        return True
+
+    def infinite_loop_check(self):
+        sccs = self.run()
+        stop_ids = {nid for nid, node in self.cfg.items() if node.kind == "stop"}
+        for comp in sccs:
+            has_cycle = len(comp) > 1 or any(
+                succ.register_id == nid
+                for nid in comp
+                for succ in self.cfg[nid].succs
+            )
+            if not has_cycle:
+                continue
+
+            has_exit = any(
+                (succ.register_id not in comp) and self.edge_feasible(self.cfg[nid], succ.register_id)
+                for nid in comp
+                for succ in self.cfg[nid].succs
+            )
+
+            stack = list(comp)
+            seen = set(comp)
+            can_reach_stop = False
+            while stack:
+                curr = stack.pop()
+                if curr in stop_ids:
+                    can_reach_stop = True
+                    break
+                for succ in self.cfg[curr].succs:
+                    sid = succ.register_id
+                    if not self.edge_feasible(self.cfg[curr], sid):
+                        continue
+                    if sid not in seen:
+                        seen.add(sid)
+                        stack.append(sid)
+
+            if not has_exit and not can_reach_stop:
+                raise TypeError(
+                    f"Infinite loop detected in circuit: {sorted(comp)}"
+                )
+

src/oqd_core/frontend/analog/cfg.py

@@ -0,0 +1,134 @@
+# Copyright 2024-2025 Open Quantum Design
+
+# Licensed under the Apache License, Version 2.0 (the "License")
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+from __future__ import annotations
+
+from oqd_compiler_infrastructure import RewriteRule
+
+from oqd_core.analysis.utils import CFGNode
+from oqd_core.interface.analog import (
+    AnalogCircuit,
+    Break,
+    Continue,
+    IfElse,
+    While,
+)
+
+
+class AnalogCFGBuilder(RewriteRule):
+    def __init__(self):
+        super().__init__()
+        self.registry = 0
+        self.cache = {}
+        self.loop_stack = []
+        self.preds = []
+        self.founder = None
+        self.last_node = None
+        self.edge_labels = None
+        self.fallthrough_labels = {}
+
+
+    def new_node(self, preds, stmt, kind = "stmt"):
+        node = CFGNode(register_id=self.registry, stmt=stmt,preds=preds, kind=kind)
+        self.cache[node.register_id] = node
+        self.registry += 1
+
+        explicit_labels = self.edge_labels or {}
+        self.edge_labels = None
+
+        for pred in node.preds:
+            label = explicit_labels.get(pred.register_id)
+            if label is None:
+                label = self.fallthrough_labels.pop(pred.register_id, None)
+            pred.add_succ(node, label=label)
+
+        return node
+
+    def walk_stmt(self, stmt, preds, edge_labels=None):
+        old = self.preds
+        old_labels = self.edge_labels
+        self.preds = preds
+        self.edge_labels = edge_labels
+        result = self(stmt)
+        self.preds = old
+        self.edge_labels = old_labels
+        return result
+
+    def walk_block(self, statements, preds, entry_label=None):
+        pred = preds
+        first = True
+        for stmt in statements:
+            edge_labels = None
+            if first and entry_label is not None:
+                edge_labels = {p.register_id: entry_label for p in pred}
+            pred = self.walk_stmt(stmt, pred, edge_labels=edge_labels)
+            first = False
+        return pred
+
+    def run(self, circuit: AnalogCircuit):
+        self.registry = 0
+        self.cache = {}
+        self.loop_stack = []
+        self.edge_labels = None
+        self.fallthrough_labels = {}
+        self.founder = self.new_node([], "start", kind="start")
+        exits = self.walk_stmt(circuit, [self.founder])
+        self.last_node = self.new_node(exits, "stop", kind="stop")
+        return self.cache
+
+    def map_AnalogCircuit(self, model: AnalogCircuit):
+        return self.walk_block(model.statements, self.preds)
+
+    def map_IfElse(self, model: IfElse):
+        node = self.new_node(self.preds, model.condition, kind="branch")
+        then_branch = self.walk_block(model.then_branch, [node], entry_label="true")
+        if model.else_branch:
+            else_branch = self.walk_block(model.else_branch, [node], entry_label="false")
+            return list(then_branch) + (list(else_branch))
+
+        self.fallthrough_labels[node.register_id] = "false"
+
+        return list(then_branch) + [node]
+
+    def map_While(self, model: While):
+        node = self.new_node(self.preds, model.condition, kind="branch")
+        self.loop_stack.append(node)
+        body = self.walk_block(model.body, [node], entry_label="true")
+        self.loop_stack.pop()
+
+        node.add_preds(body)
+        self.fallthrough_labels[node.register_id] = "false"
+
+        return node.exit_nodes + [node]
+
+    def map_Break(self, model: Break):
+        if not self.loop_stack:
+            raise TypeError("break statement used outside loop")
+        break_node = self.new_node(self.preds, model)
+        self.loop_stack[-1].exit_nodes.append(break_node)
+        self.fallthrough_labels[break_node.register_id] = "break"
+        return []
+
+    def map_Continue(self, model: Continue):
+        if not self.loop_stack:
+            raise TypeError("continue statement used outside loop")
+        continue_node = self.new_node(self.preds, model)
+        self.loop_stack[-1].add_pred(continue_node, label="continue")
+        return []
+
+    def generic_map(self, model):
+        return [self.new_node(self.preds, model)]
+
+