fix(mgb/gopt): fix remove redundant typecvt pass

GitOrigin-RevId: 6a7957e362931302ac883e05031b6be0ca42b0d2

src/gopt/impl/misc.cpp

@@ -635,15 +635,19 @@ void RemoveRedundantTypeCvtPass::apply(OptState& opt) const {
 
     auto on_opr = [&](OperatorNodeBase* opr) {
         if (auto tc0 = try_cast_as_op<opr::TypeCvt>(opr)) {
-            if (auto tc1 = try_cast_as_op<opr::TypeCvt>(tc0->input(0))) {
+            auto inp0 = rewriter.get_var(tc0->input(0));
+            if (auto tc1 = try_cast_as_op<opr::TypeCvt>(inp0)) {
                 if (should_remove(tc0->param(), tc1->param())) {
+                    auto inp1 = tc1->input(0);
+                    mgb_assert(!rewriter.has_manual_replace(inp1));
                     // TypeCvt returns the input var if its dtype is already
                     // dest_type
-                    auto fold = opr::TypeCvt::make(tc1->input(0), tc0->param());
+                    auto fold = opr::TypeCvt::make(inp1, tc0->param());
                     rewriter.replace_var(
                             tc0->output(0), fold.node(),
                             mgb_cstr_log("cvt_b(cvt_a(x)) -> cvt_b(x)"));
                 }
+                return;
             }
         }
         rewriter.auto_replace_outputs(opr);

src/gopt/test/misc.cpp

@@ -395,6 +395,12 @@ TEST_PASS(RemoveRedundantTypeCvtPass, Basic) {
     check(x_fp16, x_fp16_fp32_fp16);
 #endif
 
+    auto x_i32 = opr::TypeCvt::make(x, dtype::Int32());
+    auto x_i32_i16 = opr::TypeCvt::make(x_i32, dtype::Int16());
+    auto x_i32_i16_i8 = opr::TypeCvt::make(x_i32_i16, dtype::Int8());
+    auto x_i8 = opr::TypeCvt::make(x, dtype::Int8());
+    check(x_i8, x_i32_i16_i8);
+
     auto x_q8 = opr::TypeCvt::make(x, dtype::QuantizedS8(0.1f));
     auto x_q8_fp32 = opr::TypeCvt::make(x_q8, dtype::Float32());
     auto x_q8_fp32_q8 = opr::TypeCvt::make(x_q8_fp32, dtype::QuantizedS8(0.1f));