diff --git a/App/lib/core/Gen/Expr/ExprGenOps.vp b/App/lib/core/Gen/Expr/ExprGenOps.vp
index d547d42..d019bc7 100644
--- a/App/lib/core/Gen/Expr/ExprGenOps.vp
+++ b/App/lib/core/Gen/Expr/ExprGenOps.vp
@@ -1332,6 +1332,42 @@ novirtual class ExprGenOps(ExprGenBase.ExprGenBase):
         lhs_fbits: int = self.get_llvm_float_bits(lhs.Ty)
         rhs_fbits: int = self.get_llvm_float_bits(rhs.Ty)
 
+        # 纯常量整型算式（两侧都是编译期整型常量）：按**精确值**折叠并按值定宽，
+        # 禁止按操作数的最小宽度回绕（现场：`1024 * 1024 * 4` 按 i16 算成 0 ⇒
+        # WINBUF_MAX_BYTES=0 ⇒ 窗口缓冲只剩几字节 ⇒ 内核 memcpy 240KB 越界读/三重故障）。
+        if lhs_bits > 0 and rhs_bits > 0 and lhs.IsConst == 1 and rhs.IsConst == 1:
+            cf_ok: int = 1
+            cf_v: int64 = 0
+            if op == ast.OpKind.Add:      cf_v = lhs.IntVal + rhs.IntVal
+            elif op == ast.OpKind.Sub:    cf_v = lhs.IntVal - rhs.IntVal
+            elif op == ast.OpKind.Mult:   cf_v = lhs.IntVal * rhs.IntVal
+            elif op == ast.OpKind.BitOr:  cf_v = lhs.IntVal | rhs.IntVal
+            elif op == ast.OpKind.BitAnd: cf_v = lhs.IntVal & rhs.IntVal
+            elif op == ast.OpKind.BitXor: cf_v = lhs.IntVal ^ rhs.IntVal
+            elif op == ast.OpKind.LShift or op == ast.OpKind.RShift:
+                if rhs.IntVal >= 0 and rhs.IntVal < 64:
+                    if op == ast.OpKind.LShift: cf_v = lhs.IntVal << rhs.IntVal
+                    else: cf_v = lhs.IntVal >> rhs.IntVal
+                else: cf_ok = 0
+            else: cf_ok = 0
+            if cf_ok != 0:
+                # 定宽：下限取操作数较宽者，只有精确值装不下才加宽（避免把 `A + 1` 这类
+                # 常量算式整体抬成 i64，引出新的“隐式窄化”报错）。
+                cf_w: int = lhs_bits if lhs_bits > rhs_bits else rhs_bits
+                if cf_v != 0:
+                    t_cf: int64 = cf_v
+                    if cf_v < 0: t_cf = cf_v ^ int64(-1)
+                    vw_cf: int = 1               # 符号位
+                    while t_cf != 0:
+                        vw_cf += 1
+                        t_cf = t_cf >> 1
+                    if vw_cf > cf_w: cf_w = vw_cf
+                if cf_w <= 8: cf_w = 8
+                elif cf_w <= 16: cf_w = 16
+                elif cf_w <= 32: cf_w = 32
+                else: cf_w = 64
+                return mlirlite.const_int(pool, cf_w, cf_v)
+
         # Float operation: use float instructions when either operand is float (must precede pointer arithmetic, since float has 0 int bits and would be mistaken for a pointer).
         if lhs_fbits != 0 or rhs_fbits != 0:
             # Determine the target float type (use the larger bit width)