[S-TIR] Fix the ScheduleError from missing guard in CheckInline

src/s_tir/meta_schedule/schedule_rule/auto_inline.cc

@@ -164,6 +164,16 @@ inline InlineType AutoInlineNode::CheckInline(const s_tir::Schedule& sch,
     if (ann.value() == "disable") return InlineType::kNoInline;
   }
   // Last cond: Check inline into the consumers or the spatial producer
+  // Skip if:
+  // - root block (no parent scope).
+  // - root block is wrapped in a For loop, then parent is non-null, but there is still no enclosing SBlockNode.
+  const StmtSRefNode* p = block_sref->parent;                   
+  for (; p != nullptr; p = p->parent) {                                                   
+    if (p->stmt->IsInstance<SBlockNode>()) break;
+  }                                                                                       
+  if (p == nullptr) {                                           
+    return InlineType::kNoInline;
+  }
   tirx::StmtSRef scope_block = s_tir::GetScopeRoot(sch->state(), block_sref,
                                                    /*require_stage_pipeline=*/false);
   if (into_consumer) {

tests/python/s_tir/meta_schedule/test_meta_schedule_schedule_rule_auto_inline.py

@@ -533,5 +533,35 @@ def main(T_full: T.Buffer((), "float32")):
     assert_structural_equal(sch.mod, Full)
 
 
+def test_no_inline_root_block():
+    @tvm.script.ir_module
+    class MaxReduction:
+        @T.prim_func
+        def main(
+            data: T.Buffer((8, 8), "float32"),
+            data_red: T.Buffer((), "float32"),
+        ):
+            T.func_attr({"tir.noalias": T.bool(True)})
+            with T.block("data_red"):
+                T.reads(data[0:8, 0:8])
+                T.writes(data_red[()])
+                with T.init():
+                    data_red[()] = T.float32(-3.4e38)
+                for i, j in T.grid(8, 8):
+                    with T.block("update"):
+                        T.reads(data_red[()], data[i, j])
+                        T.writes(data_red[()])
+                        data_red[()] = T.max(data_red[()], data[i, j])
+
+    target = Target("llvm")
+    (space,) = generate_design_space(
+        kind="llvm",
+        mod=MaxReduction,
+        target=target,
+        types=ms.schedule_rule.AutoInline,
+    )
+    tvm.ir.assert_structural_equal(lhs=space.mod, rhs=MaxReduction)
+
+
 if __name__ == "__main__":
     tvm.testing.main()