[BUGFIX][TIR] Skip wholly-constant expressions in CSE

src/tirx/transform/common_subexpr_elim.cc

@@ -49,6 +49,9 @@
  *   - It is not a leaf (Var, IntImm, FloatImm, StringImm).
  *   - It does not contain Call or BufferLoad (side-effects / memory dependence).
  *   - It is not Ramp or Broadcast (hardware-specific vector ops).
+ *   - It is not a wholly-constant expression (no Var anywhere in the tree).
+ *     Constant subtrees provide no CSE benefit — the constant folder
+ *     collapses them — and lifting them only adds noise like `cse_v = 1`.
  *
  * Scope tree
  * ----------
@@ -263,6 +266,10 @@ class CSEPlanner : public StmtExprVisitor {
    *   - Not a Call or BufferLoad (side effects / memory dependence).
    *   - Not Ramp or Broadcast (hardware-specific vector construction).
    *   - Does not transitively contain any forbidden node.
+   *   - Is not a wholly-constant expression (contains no Var in its tree).
+   *     Compound expressions like `Cast(int32, 1)` or `Min(1, 2)` pass the
+   *     leaf-only checks above but are still compile-time constants — the
+   *     constant folder will collapse them, so hoisting only adds noise.
    *
    * \param expr The expression to check.
    * \return true if the expression can participate in CSE.
@@ -275,6 +282,13 @@ class CSEPlanner : public StmtExprVisitor {
     if (IsForbiddenNode(expr)) return false;
     if (expr.as<RampNode>() || expr.as<BroadcastNode>()) return false;
     if (CheckContains::ExprContains(expr, IsForbiddenNode)) return false;
+    // Reject wholly-constant expressions (no Var anywhere in the tree).
+    // BufferLoad is already filtered above by IsForbiddenNode, so
+    // "contains no Var" is sufficient to declare the expression a
+    // compile-time constant. Hoisting it adds noise; the constant
+    // folder will collapse it.
+    auto contains_var = [](const PrimExpr& e) { return e.as<VarNode>() != nullptr; };
+    if (!CheckContains::ExprContains(expr, contains_var)) return false;
     return true;
   }
 

tests/python/tirx-transform/test_tir_transform_common_subexpr_elim.py

@@ -713,6 +713,41 @@ def test_let_floordiv_pattern():
     assert "cse_v" not in script, f"CSE incorrectly extracted from Let body:\n{script}"
 
 
+# =====================================================================
+# T22: Wholly-constant Cast is not lifted
+# `Cast(int32, 1)` is a compound expression whose leaves are constants
+# only. The constant folder collapses it; CSE adds noise only.
+# =====================================================================
+def test_no_lift_constant_expression():
+    @tvm.script.ir_module
+    class Before:
+        @T.prim_func
+        def main(B: T.Buffer((50,), "int32"), i1: T.int32, i2: T.int32):
+            B[i1] = T.Cast("int32", 1) + i1
+            B[i2] = T.Cast("int32", 1) + i2
+
+    after = tvm.tirx.transform.CommonSubexprElim()(Before)
+    tvm.ir.assert_structural_equal(after, Before)
+    assert "cse_v" not in after["main"].script()
+
+
+# =====================================================================
+# T23: Wholly-constant Min is not lifted
+# `T.min(1, 2)` is a compound constant; CSE must not lift it.
+# =====================================================================
+def test_no_lift_constant_min():
+    @tvm.script.ir_module
+    class Before:
+        @T.prim_func
+        def main(B: T.Buffer((50,), "int32"), i1: T.int32, i2: T.int32):
+            B[i1] = T.min(1, 2) + i1
+            B[i2] = T.min(1, 2) + i2
+
+    after = tvm.tirx.transform.CommonSubexprElim()(Before)
+    tvm.ir.assert_structural_equal(after, Before)
+    assert "cse_v" not in after["main"].script()
+
+
 if __name__ == "__main__":
     test_basic()
     test_if_single_branch()
@@ -735,3 +770,5 @@ def test_let_floordiv_pattern():
     test_let_value_cse()
     test_nested_let_no_extraction()
     test_let_floordiv_pattern()
+    test_no_lift_constant_expression()
+    test_no_lift_constant_min()