fix(mgb/gopt): add error message when input dtype is not equal to param dtype in BN2Elemwise pass

GitOrigin-RevId: 3d09a2a12eaca7cc39c51a5004230a466272e936

src/gopt/impl/inference.cpp

@@ -1686,6 +1686,13 @@ void ConvertBatchNormToElemwisePass::apply(OptState& state) const {
                 SymbolVar invsqrt_variance = opr::PowC::make(variance
                         + variance.make_scalar_dt(float(bn->param().epsilon)), {-0.5});
                 auto res = scale * (x - mean) * invsqrt_variance + bias;
+                if (x.dtype() != res.dtype()) {
+                    mgb_throw(MegBrainError,
+                              "BN's input dtype %s is not compatible with "
+                              "param dtype %s when fusing BN. You may need to "
+                              "dump FP32 model.",
+                              x.dtype().name(), res.dtype().name());
+                }
                 rewriter.replace_var(
                         opr->output(4), res.node(),
                         mgb_cstr_log(