[MLIR] Disable support for boolean type in MLIR (#3434)

* [MLIR] Disable support for boolean type in MLIR

Ops on boolean types are currently not supported by MLIR Compiler until
the proper i1<->i8 type conversion mechanism is in place.

* Add example.

* Fix typo

src/contrib/mlir/pass/mlir_subgraph_extraction.cpp

@@ -272,6 +272,15 @@ bool MLIRSubgraphExtractionPass::run_on_function(std::shared_ptr<Function> func)
 
 bool MLIRSubgraphExtractionPass::is_supported_mlir_op(std::shared_ptr<Node> node)
 {
+    // Disable any op using boolean type until we have support for i1<->i8 conversion in MLIR.
+    // Otherwise, we would generate code like this:
+    //   %0 = icmp %a, %b : i1
+    //   store %0, %c[%arg1] : i8  // Type error: trying to store an i1 into an i8.
+    if (((element::Type_t)node->get_element_type()) == element::Type_t::boolean)
+    {
+        return false;
+    }
+
     if (TI(Parameter) == TI(*node) || TI(Result) == TI(*node))
     {
         return true;