feat(gen): 控制流汇合 Meet（M2.2）

- VarGenMixin：life_capture/life_restore/life_join（作用域链快照，池上 [count,(entry,life)…] 数组）。 - StmtGenCifMixin.translate_if：进分支前快照、then 末快照、else 前复位、出口按 min 合并。 - StmtGenMixin：while/for 统一在语句分派处 capture→run→join（一处覆盖全部迭代形态与解糖，含 0 次迭代路径）。

App/lib/core/Gen/Stmt/StmtGenCifMixin.vp

@@ -708,6 +708,9 @@ novirtual class StmtGenCifMixin:
         if has_else == 1: mlirlite.build_cond_br(builder, cond_i1, then_bb, else_bb)
         else: mlirlite.build_cond_br(builder, cond_i1, then_bb, merge_bb)
 
+        # 生命期汇合：进入分支前快照（else 分支需从该状态重新开始，见 §11 控制流 Meet）
+        life_snap0: sizet* = self.Gen.VarGen.life_capture(trans)
+
         # 5. translate the then body; reset the merge-reachable flag first (nested control flow
         # overwrites it, so the branch-tail check must not see a stale value from before this If).
         trans._ctrl_merge_reachable = 1
@@ -730,9 +733,14 @@ novirtual class StmtGenCifMixin:
                 mlirlite.build_br(builder, merge_bb)
                 then_branches_merge = 1
 
+        # then 末状态快照（供两端 Meet：先复位到 if 前状态，再与 then 末状态合并）
+        life_snap1: sizet* = self.Gen.VarGen.life_capture(trans)
+
         # 6. translate the else body (if any)
         else_branches_merge: int = 0
         if has_else == 1:
+            # 复位到 if 前状态，让 else 分支从同一基线出发（否则会看到 then 分支写入的 Life）
+            self.Gen.VarGen.life_restore(life_snap0)
             # as in then: reset the flag to avoid stale values from the then branch
             trans._ctrl_merge_reachable = 1
             mlirlite.position_at_end(builder, else_bb)
@@ -748,6 +756,10 @@ novirtual class StmtGenCifMixin:
                     mlirlite.build_br(builder, merge_bb)
                     else_branches_merge = 1
 
+        # 生命期汇合：有 else → 与 then 末状态 Meet；无 else → 与 if 前状态 Meet（else 路径=跳过）
+        if has_else == 1: self.Gen.VarGen.life_join(life_snap1)
+        else: self.Gen.VarGen.life_join(life_snap0)
+
         # 7. merge reachability (used by tail-flow checks): without else cond_br always reaches
         #    merge; with else, any branch br reaching merge suffices; only all-return is unreachable.
         trans._ctrl_merge_reachable = 1

App/lib/core/Gen/Stmt/StmtGenMixin.vp

@@ -51,9 +51,19 @@ novirtual class StmtGenMixin(StmtGenDeclMixin.StmtGenDeclMixin):
             return self.Gen.FuncGen.translate_nested_function_def(trans, node)
         elif k == ast.ASTKind.Return: return self.Gen.StmtGenCif.translate_return(trans, node)
         elif k == ast.ASTKind.If: return self.Gen.StmtGenCif.translate_if(trans, node)
-        elif k == ast.ASTKind.While: return self.Gen.StmtGenCif.translate_while(trans, node)
+        elif k == ast.ASTKind.While:
+            # 循环生命期汇合：循环可能 0 次执行，出口状态须与进入前状态 Meet（见 §11 控制流 Meet）
+            snap_wh: sizet* = self.Gen.VarGen.life_capture(trans)
+            rc_wh: int = self.Gen.StmtGenCif.translate_while(trans, node)
+            self.Gen.VarGen.life_join(snap_wh)
+            return rc_wh
         elif k == ast.ASTKind.AugAssign: return self.Gen.AssignGen.translate_augassign(trans, node)
-        elif k == ast.ASTKind.For: return self.Gen.StmtGenCif.translate_for(trans, node)
+        elif k == ast.ASTKind.For:
+            # 同上：for 的各迭代形态（range/指针/数组/容器/解糖）统一在此收口
+            snap_fr: sizet* = self.Gen.VarGen.life_capture(trans)
+            rc_fr: int = self.Gen.StmtGenCif.translate_for(trans, node)
+            self.Gen.VarGen.life_join(snap_fr)
+            return rc_fr
         elif k == ast.ASTKind.ClassDef: return self.Gen.ClassGenDef.translate_class_def(trans, node)
         elif k == ast.ASTKind.Import: return self.Gen.ImportsGen.translate_import(trans, node)
         elif k == ast.ASTKind.ImportFrom:

App/lib/core/Gen/VarGenMixin.vp

@@ -204,6 +204,61 @@ novirtual class VarGenMixin:
         """Meet of two life tags (min); used where branches join"""
         return a if a < b else b
 
+    # life_capture - 快照当前作用域链上所有变量的 LifeTag（供控制流汇合 Meet）。
+    # 返回池上数组：buf[0]=count，其后每项 (entry_ptr, life) 各占一个 sizet 槽；失败返回 None。
+    def life_capture(self, trans: HT.Translator*) -> sizet*:
+        """Snapshot every in-scope variable's LifeTag (control-flow merge support)"""
+        if trans is None or trans.SymTab is None: return None
+        pool: memhub.MemBuddy* = trans.Pool
+        if pool is None: return None
+        cnt: sizet = 0
+        sc_c: GenTypes.Scope* = trans.SymTab.Current
+        while sc_c is not None:
+            cnt += sizet(sc_c.VarCount)
+            sc_c = sc_c.Parent
+        buf: sizet* = sizet*(pool.alloc(8 * (2 * cnt + 2)))
+        if buf is None: return None
+        buf[0] = cnt
+        idx: sizet = 1
+        esz: uint64 = uint64(GenTypes.VarEntry.__sizeof__())
+        sc: GenTypes.Scope* = trans.SymTab.Current
+        while sc is not None:
+            if sc.Vars is not None and sc.VarCount > 0:
+                j: int = 0
+                while j < sc.VarCount:
+                    ent: GenTypes.VarEntry* = GenTypes.VarEntry*(uint64(sc.Vars) + uint64(j) * esz)
+                    buf[idx * 2] = sizet(uint64(ent))
+                    buf[idx * 2 + 1] = sizet(ent.Life)
+                    idx += 1
+                    j += 1
+            sc = sc.Parent
+        return buf
+
+    # life_restore - 把快照写回各变量（让 else 分支从 if 之前的状态开始）。
+    def life_restore(self, buf: sizet*) -> int:
+        """Restore LifeTag values from a snapshot; 0=ok / 1=no snapshot"""
+        if buf is None: return 1
+        cnt: sizet = buf[0]
+        i: sizet = 1
+        while i <= cnt:
+            ent: GenTypes.VarEntry* = GenTypes.VarEntry*(uint64(buf[i * 2]))
+            if ent is not None: ent.Life = int(buf[i * 2 + 1])
+            i += 1
+        return 0
+
+    # life_join - 当前值与快照逐项 Meet（汇合：任一路径为短命即取短命）。
+    def life_join(self, buf: sizet*) -> int:
+        """Meet the current LifeTags with a snapshot; 0=ok / 1=no snapshot"""
+        if buf is None: return 1
+        cnt: sizet = buf[0]
+        i: sizet = 1
+        while i <= cnt:
+            ent: GenTypes.VarEntry* = GenTypes.VarEntry*(uint64(buf[i * 2]))
+            if ent is not None:
+                ent.Life = self.life_meet(ent.Life, int(buf[i * 2 + 1]))
+            i += 1
+        return 0
+
     # add_var - add a variable to the variable table
     # ============================================================
     def add_var(self, vars_ptr: GenTypes.VarEntry*, var_count: int, name: str, alloca: mlirlite.Value*) -> int: