diff --git a/crates/oxide_dce/src/lib.rs b/crates/oxide_dce/src/lib.rs
index d821fb3a..240fa2dd 100644
--- a/crates/oxide_dce/src/lib.rs
+++ b/crates/oxide_dce/src/lib.rs
@@ -35,7 +35,10 @@ pub fn dce(f: &mut IRFunction) {
     let dead = keep.iter().filter(|k| !**k).count();
     dce_info!("DCE: removing {} dead instructions", dead);
     // Pass C：mark-sweep 一次性重建 insts + label_pos 重映射。
-    rebuild::pass_c_sweep(f, &keep);
+    // keep 全真时重建为恒等变换（新旧下标相同、label 重映射为恒等），零删除直接跳过。
+    if dead > 0 {
+        rebuild::pass_c_sweep(f, &keep);
+    }
 }
 
 /// 精确二轮：liveness 驱动的死指令 + 局部死 STORE_VAR 删除。
@@ -53,6 +56,9 @@ pub fn dce_precise(f: &mut IRFunction, live: &LiveInfo) {
     }
     let mut keep = vec![true; f.insts.len()];
     precise_sweep::pass_dead_with_liveness(f, live, &mut keep);
-    // mark-sweep 一次性重建
-    rebuild::pass_c_sweep(f, &keep);
+    // keep 全真时重建为恒等变换，零删除直接跳过；重建条件与快速路径守卫同源（仅 keep 计数）。
+    let dead = keep.iter().filter(|k| !**k).count();
+    if dead > 0 {
+        rebuild::pass_c_sweep(f, &keep);
+    }
 }
diff --git a/crates/oxide_dce/tests/conservative_unit.rs b/crates/oxide_dce/tests/conservative_unit.rs
index 85152a5d..2fb09efe 100644
--- a/crates/oxide_dce/tests/conservative_unit.rs
+++ b/crates/oxide_dce/tests/conservative_unit.rs
@@ -55,3 +55,25 @@ fn if_else_both_branches_reachable_kept() {
     assert_eq!(f.label_pos, vec![Some(3), Some(4)], "存活 label 重映射到新下标");
     assert_eq!(f.label_count, 2, "label_count 保持原值，不参与重建");
 }
+
+/// 全存活函数：含 label 与 nested 的函数过 dce 后 insts 与 label_pos 逐位不变。
+/// 零删除时 Pass C 重建为恒等变换，快速路径跳过重建后输出须与执行前逐位一致。
+#[test]
+fn all_live_function_unchanged() {
+    let mut f = IRFunction::new();
+    f.insts.push(Inst::load_const(Operand::Reg(1), 0)); // 0: label 0 目标，值被 CALL 使用
+    f.insts.push(Inst::call(Operand::Reg(2), Operand::Reg(1), Operand::Reg(3), 1)); // 1: 非纯，永不删
+    f.insts
+        .push(Inst::new(OpCode::RETURN, Operand::Reg(2), Operand::None, Operand::None)); // 2
+    f.label_pos = vec![Some(0)];
+    f.label_count = 1;
+    f.nested.push(IRFunction::new()); // nested 不递归不回收
+
+    let before_insts = f.insts.clone();
+    let before_labels = f.label_pos.clone();
+    dce(&mut f);
+    assert_eq!(f.insts, before_insts, "全存活时 insts 逐位不变");
+    assert_eq!(f.label_pos, before_labels, "全存活时 label_pos 逐位不变");
+    assert_eq!(f.label_count, 1, "label_count 保持原值");
+    assert_eq!(f.nested.len(), 1, "nested 不触碰");
+}
diff --git a/crates/oxide_dce/tests/precise_unit.rs b/crates/oxide_dce/tests/precise_unit.rs
index b43d8fac..f89baa14 100644
--- a/crates/oxide_dce/tests/precise_unit.rs
+++ b/crates/oxide_dce/tests/precise_unit.rs
@@ -235,3 +235,32 @@ fn empty_function_unchanged() {
     dce_precise(&mut f, &live);
     assert!(f.insts.is_empty());
 }
+
+/// 零删除快速路径：live 集全活时 dce_precise 输出逐位不变。
+/// 标记后 keep 全真，Pass C 重建为恒等变换，跳过重建须与执行前逐位一致。
+#[test]
+fn all_live_precise_unchanged() {
+    let mut f = IRFunction::new();
+    f.insts.push(Inst::load_const(Operand::Reg(1), 0)); // 0: label 0 目标，r1 后续活
+    f.insts.push(Inst::new(
+        oxide_bytecode::opcode::OpCode::STORE_VAR,
+        Operand::Reg(2),
+        Operand::Reg(1),
+        Operand::Imm(0),
+    )); // 1: r2 后续活
+    f.insts.push(Inst::new(
+        oxide_bytecode::opcode::OpCode::RETURN,
+        Operand::Reg(2),
+        Operand::None,
+        Operand::None,
+    )); // 2
+    f.label_pos = vec![Some(0)];
+    f.label_count = 1;
+
+    let before_insts = f.insts.clone();
+    let before_labels = f.label_pos.clone();
+    // 全活：每个 def 寄存器都在其 live_after 中
+    run_precise(&mut f, &[&[1, 2], &[2], &[]], 5);
+    assert_eq!(f.insts, before_insts, "全活时 insts 逐位不变");
+    assert_eq!(f.label_pos, before_labels, "全活时 label_pos 逐位不变");
+}