[Relax][VM] Improve diagnostics for unlowered Relax operators

src/relax/backend/vm/codegen_vm.cc

@@ -157,8 +157,11 @@ class CodeGenVM : public ExprFunctor<Instruction::Arg(const Expr&)> {
       } else {
         // every "normal" operator is lowered to a global var in the IRModule. The Attrs for those
         // ops are handled in a pass when lowering them to TIR.
-        TVM_FFI_THROW(InternalError) << "CodeGenVM cannot handle this intrinsic now:\n"
-                                     << call_node->op;
+        TVM_FFI_THROW(InternalError)
+            << "CodeGenVM cannot emit this Relax operator directly. "
+            << "Run the appropriate lowering pass, or route the operator to an external "
+            << "codegen before VM codegen.\nOffending call:\n"
+            << call;
       }
     } else {
       EmitNormalCall(call, dst_reg);

src/relax/backend/vm/codegen_vm_tir.cc

@@ -246,8 +246,11 @@ class CodeGenVMTIR : public ExprFunctor<ffi::Optional<PrimExpr>(const Expr&)> {
       } else {
         // every "normal" operator is lowered to a global var in the IRModule. The Attrs for those
         // ops are handled in a pass when lowering them to TIR.
-        TVM_FFI_THROW(InternalError) << "CodeGenVMTIR cannot handle this intrinsic now:\n"
-                                     << call_node->op;
+        TVM_FFI_THROW(InternalError)
+            << "CodeGenVMTIR cannot emit this Relax operator directly. "
+            << "Run the appropriate lowering pass, or route the operator to an external "
+            << "codegen before VM codegen.\nOffending call:\n"
+            << call;
       }
     } else {
       EmitNormalCall(call, dst_reg);

tests/python/relax/test_vm_build.py

@@ -84,6 +84,30 @@ def foo(x: R.Tensor((3, 4), "float32"), y: R.Tensor((3, 4), "float32")):
     tvm.testing.assert_allclose(inp2.numpy(), inp1.numpy(), rtol=1e-7, atol=1e-7)
 
 
+def test_vm_compile_unlowered_operator_error(exec_mode):
+    @tvm.script.ir_module
+    class Conv2dTranspose:
+        @R.function
+        def main(
+            x: R.Tensor((1, 4, 4, 1), "float32"),
+            w: R.Tensor((1, 2, 3, 3), "float32"),
+        ):
+            gv = R.nn.conv2d_transpose(
+                x,
+                w,
+                data_layout="NHWC",
+                kernel_layout="IOHW",
+            )
+            return gv
+
+    mod = relax.transform.LegalizeOps()(Conv2dTranspose)
+    with pytest.raises(
+        tvm.error.InternalError,
+        match=r"(?s)Offending call:.*relax\.nn\.conv2d_transpose.*data_layout.*NHWC",
+    ):
+        relax.build(mod, target="llvm", exec_mode=exec_mode)
+
+
 def test_match_check(exec_mode):
     @tvm.script.ir_module
     class TestMatchCheck: