feat(mlirlite): 新增 IRBuilder.build_store_at_entry，支持在入口块写入以建立支配关系

M3 owned slife 的所有权影子标志必须在函数入口块置 0：赋值语句可能落在 if/while 里而运行期不执行，那种路径上出口 free 的是未初始化栈垃圾。实现照搬 build_alloca_at_entry：文本插到入口终止符之前，保证支配所有路径。

mlirlite/__builder.vp

@@ -266,6 +266,38 @@ novirtual class IRBuilder:
         self._emit(line)
 
 
+    def build_store_at_entry(self, val: Value*, ptr: Value*,
+                             is_volatile: int = 0):
+        """store [volatile ]<val_ty> <val>, <ptr_ty> <ptr>, emitted in the **entry block**
+        (inserted before the entry terminator) so the write dominates every path.
+
+        Used to zero/null-initialize a local slot at function entry: a slot that is not
+        assigned on some path must still hold a safe value, e.g. the M3 owned-slife guard —
+        the exit-time `free(load slot)` must be `free(NULL)` (a no-op) instead of freeing
+        uninitialized stack garbage. Mirrors build_alloca_at_entry's insertion strategy.
+        """
+        if self is None or val is None or ptr is None: return
+        pool: memhub.MemBuddy* = self.Pool
+        func: Function* = self.Func
+        if func is None or func.Blocks is None:
+            self.build_store(val, ptr, is_volatile)
+            return
+        blocks: GSList[BasicBlock]* = func.Blocks
+        entry_blk: BasicBlock* = blocks.Head
+        if entry_blk is None:
+            self.build_store(val, ptr, is_volatile)
+            return
+        val_ty_s: str = self._type_str(val.Ty)
+        ptr_ty_s: str = self._type_str(ptr.Ty)
+        line: str = pool.alloc(_LINE_CAP)
+        if line is None: return
+        if is_volatile != 0:
+            viperlib.snprintf(line, _LINE_CAP, "store volatile %s %s, %s %s", val_ty_s, val.Name, ptr_ty_s, ptr.Name)
+        else:
+            viperlib.snprintf(line, _LINE_CAP, "store %s %s, %s %s", val_ty_s, val.Name, ptr_ty_s, ptr.Name)
+        block_insert_text_before_terminator(pool, entry_blk, line)
+
+
     # ============================================================
     # Binary operation instructions
     # ============================================================
@@ -1298,6 +1330,14 @@ def build_store(builder: IRBuilder*, val: Value*, ptr: Value*,
     builder.build_store(val, ptr, is_volatile)
 
 
+def build_store_at_entry(builder: IRBuilder*, val: Value*, ptr: Value*,
+                         is_volatile: int = 0):
+    """store [volatile ]<val_ty> <val>, <ptr_ty> <ptr> emitted in the entry block
+    (before the entry terminator) so the write dominates every path; used for
+    null-initializing a local slot at function entry (M3 owned-slife guard)."""
+    builder.build_store_at_entry(val, ptr, is_volatile)
+
+
 # ============================================================
 # Binary operation instructions
 # ============================================================

mlirlite/__init__.vp

@@ -62,6 +62,7 @@ from .__builder import (
     builder_cur_block_is_terminated,
     builder_set_debug_location, builder_clear_debug_location,
     build_alloca, build_alloca_aligned, build_alloca_at_entry, build_load, build_store,
+    build_store_at_entry,
     build_add, build_sub, build_mul, build_sdiv, build_udiv, build_srem, build_urem,
     build_and, build_or, build_xor, build_shl, build_lshr, build_ashr,
     build_fadd, build_fsub, build_fmul, build_fdiv, build_frem, build_fneg,