Use the generic form when printing from the python bindings and the verifier fails

[mehdi_amini]

Summary

This reduces the chances of segfault. While it is a good practice to ensure
robust custom printers, it is unfortunately common to have them crash on
invalid input.

[stellaraccident]

Thanks! Been meaning to add the verify hook for a while.

mlir/include/mlir-c/IR.h

 MLIR_CAPI_EXPORTED void mlirOperationPrintWithFlags(MlirOperation op,
                                                     MlirOpPrintingFlags flags,
                                                     MlirStringCallback callback,
                                                     void *userData);
 
 /// Prints an operation to stderr.
 MLIR_CAPI_EXPORTED void mlirOperationDump(MlirOperation op);
 
+/// Verify the operation and return true if it passes, false if it fails.
+MLIR_CAPI_EXPORTED bool mlirOperationVerify(MlirOperation op);
+
 //===----------------------------------------------------------------------===//
 // Region API.
 //===----------------------------------------------------------------------===//
 
 /// Creates a new empty region and transfers ownership to the caller.
 MLIR_CAPI_EXPORTED MlirRegion mlirRegionCreate();
 
 /// Takes a region owned by the caller and destroys it.

mlir/lib/Bindings/Python/IRModules.cpp

 void PyOperationBase::print(py::object fileObject, bool binary,
                             llvm::Optional<int64_t> largeElementsLimit,
                             bool enableDebugInfo, bool prettyDebugInfo,
                             bool printGenericOpForm, bool useLocalScope) {
   PyOperation &operation = getOperation();
   operation.checkValid();
   if (fileObject.is_none())
     fileObject = py::module::import("sys").attr("stdout");
+
+  if (!printGenericOpForm && !mlirOperationVerify(operation)) {
+    fileObject.attr("write")("// Verification failed, printing generic form\n");
+    printGenericOpForm = true;
+  }
+
   MlirOpPrintingFlags flags = mlirOpPrintingFlagsCreate();
   if (largeElementsLimit)
     mlirOpPrintingFlagsElideLargeElementsAttrs(flags, *largeElementsLimit);
   if (enableDebugInfo)
     mlirOpPrintingFlagsEnableDebugInfo(flags, /*prettyForm=*/prettyDebugInfo);
   if (printGenericOpForm)
     mlirOpPrintingFlagsPrintGenericOpForm(flags);
 

mlir/lib/CAPI/IR/IR.cpp

 #include "mlir/CAPI/IR.h"
 #include "mlir/CAPI/Support.h"
 #include "mlir/CAPI/Utils.h"
 #include "mlir/IR/Attributes.h"
 #include "mlir/IR/BuiltinOps.h"
 #include "mlir/IR/Dialect.h"
 #include "mlir/IR/Operation.h"
 #include "mlir/IR/Types.h"
+#include "mlir/IR/Verifier.h"
 #include "mlir/Parser.h"
 
 using namespace mlir;
 
 //===----------------------------------------------------------------------===//
 // Context API.
 //===----------------------------------------------------------------------===//
 

 void mlirOperationPrintWithFlags(MlirOperation op, MlirOpPrintingFlags flags,
                                  MlirStringCallback callback, void *userData) {
   detail::CallbackOstream stream(callback, userData);
   unwrap(op)->print(stream, *unwrap(flags));
 }
 
 void mlirOperationDump(MlirOperation op) { return unwrap(op)->dump(); }
 
+bool mlirOperationVerify(MlirOperation op) {
+  return succeeded(verify(unwrap(op)));
+}
+
 //===----------------------------------------------------------------------===//
 // Region API.
 //===----------------------------------------------------------------------===//
 
 MlirRegion mlirRegionCreate() { return wrap(new Region); }
 
 MlirBlock mlirRegionGetFirstBlock(MlirRegion region) {
   Region *cppRegion = unwrap(region);

mlir/test/Bindings/Python/ir_operation.py

except ValueError as e:
     print(e)
   else:
     assert False, "Expected exception"
 
   # CHECK: %1 = "custom.one_result"() : () -> f32
   print(module.body.operations[2])
 
 run(testSingleResultProperty)
+
+# CHECK-LABEL: TEST: testPrintInvalidOperation
+def testPrintInvalidOperation():
+  ctx = Context()
+  with Location.unknown(ctx):
+    module = Operation.create("module", regions=1)
+    # This block does not have a terminator, it may crash the custom printer.
+    # Verify that we fallback to the generic printer for safety.
+    block = module.regions[0].blocks.append()
+    print(module)
+    # CHECK: // Verification failed, printing generic form
+    # CHECK: "module"() ( {
+    # CHECK: }) : () -> ()
+run(testPrintInvalidOperation)