llvm(py): introduce BuildCtx + trace hub; refactor if-merge prepass + PHI wiring into module; unify logs; ctx-enable compare/ret/call/boxcall/externcall/typeop/newbox/safepoint; curated smoke option for if-merge; README updates; keep behavior stable

src/llvm_py/cfg/utils.py

@@ -0,0 +1,36 @@
+"""
+CFG utilities
+Build predecessor/successor maps and simple helpers.
+"""
+
+from typing import Dict, List, Any, Tuple
+
+def build_preds_succs(block_by_id: Dict[int, Dict[str, Any]]) -> Tuple[Dict[int, List[int]], Dict[int, List[int]]]:
+    """Construct predecessor and successor maps from MIR(JSON) blocks."""
+    succs: Dict[int, List[int]] = {}
+    preds: Dict[int, List[int]] = {}
+    for b in block_by_id.values():
+        bid = int(b.get('id', 0))
+        preds.setdefault(bid, [])
+    for b in block_by_id.values():
+        src = int(b.get('id', 0))
+        for inst in b.get('instructions', []) or []:
+            op = inst.get('op')
+            if op == 'jump':
+                t = inst.get('target')
+                if t is not None:
+                    t = int(t)
+                    succs.setdefault(src, []).append(t)
+                    preds.setdefault(t, []).append(src)
+            elif op == 'branch':
+                th = inst.get('then'); el = inst.get('else')
+                if th is not None:
+                    th = int(th)
+                    succs.setdefault(src, []).append(th)
+                    preds.setdefault(th, []).append(src)
+                if el is not None:
+                    el = int(el)
+                    succs.setdefault(src, []).append(el)
+                    preds.setdefault(el, []).append(src)
+    return preds, succs
+