Update tests/column_utilities to use experimental::equality row comparator

[divyegala]

This PR is a part of #11844

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[divyegala]

@ttnghia all the mixed type test failures are now solved, these are the only failing tests. Any advice would be appreciated:

[ RUN      ] FixedPointTestAllReps/0.SimpleFixedPointColumnWrapper
unknown file: Failure
C++ exception with description "CUDF failure at: /opt/conda/conda-bld/work/cpp/src/table/row_operators.cu:337: Cannot compare tables with different column types" thrown in the test body.

[ RUN      ] StringsConvertTest.ToFixedPointLargeScale
unknown file: Failure
C++ exception with description "CUDF failure at: /opt/conda/conda-bld/work/cpp/src/table/row_operators.cu:337: Cannot compare tables with different column types" thrown in the test body.

[ RUN      ] JsonPathTests.GetJsonObjectEmptyQuery
unknown file: Failure
C++ exception with description "CUDF failure at: /opt/conda/conda-bld/work/cpp/src/strings/strings_column_view.cpp:31: strings column has no children" thrown in the test body.

[ RUN      ] StringsSplitTest.AllNullsCase
unknown file: Failure
C++ exception with description "CUDF failure at: /opt/conda/conda-bld/work/cpp/src/strings/strings_column_view.cpp:31: strings column has no children" thrown in the test body.

[divyegala]

@davidwendt according to your baseline report, column_utilities.cu takes around ~14 minutes to build. In this PR, it takes around ~10 minutes https://downloads.rapids.ai/ci/cudf/pull-request/12777/121e45b/cpp_cuda11_x86_64.BuildMetricsReport.html

[ttnghia]

The first two failed tests compare decimals with different scales. I'm not sure if we should continue to support it or not (for the new comparator). Please initialize a discussion on Slack to get more feedback for it.

The last two failed tests are due to comparing strings in a strings column having all-nulls (which doesn't have a child column). I believe this is a bug. So you need to file a bug issue for it, then either fix that bug before this PR can proceed, or xfail these two tests.

[davidwendt]

@davidwendt according to your baseline report, column_utilities.cu takes around ~14 minutes to build. In this PR, it takes around ~10 minutes https://downloads.rapids.ai/ci/cudf/pull-request/12777/121e45b/cpp_cuda11_x86_64.BuildMetricsReport.html

Thanks. I'd still like to consider this change: #12777 (comment)

[davidwendt]

This PR uncovers a bug in this code:

cudf/cpp/src/copying/purge_nonempty_nulls.cu

Lines 37 to 54 in 84ac1d5

	bool has_nonempty_null_rows(cudf::column_view const& input, rmm::cuda_stream_view stream)
	{
	if (not input.has_nulls()) { return false; } // No nulls => no dirty rows.
	// Cross-reference nullmask and offsets.
	auto const type = input.type().id();
	auto const offsets = (type == type_id::STRING) ? (strings_column_view{input}).offsets()
	: (lists_column_view{input}).offsets();
	auto const d_input = cudf::column_device_view::create(input, stream);
	auto const is_dirty_row = [d_input = *d_input, offsets = offsets.begin<size_type>()] __device__(
	size_type const& row_idx) {
	return d_input.is_null_nocheck(row_idx) && (offsets[row_idx] != offsets[row_idx + 1]);
	};
	auto const row_begin = thrust::counting_iterator<cudf::size_type>(0);
	auto const row_end = row_begin + input.size();
	return thrust::count_if(rmm::exec_policy(stream), row_begin, row_end, is_dirty_row) > 0;
	}

Accessing data at null rows is considered undefined behavior which this function does intentionally. Both an all-null strings column and an empty strings column may not have children. I believe that is the same case for list columns though it may actually have an empty child column simply to identify its type.

I propose this function could be fixed to handle this correctly in this PR by adding the following if-statement near the top:

if ((input.size() == input.null_count()) && (input.num_children() == 0)) { return false; }

[davidwendt]

For the fixed-point error, it appears that the intention was to be able to compare fixed-point values in different scales. The FixedPointTestAllReps/SimpleFixedPointColumnWrapper gtests specifically tests this.
I propose to relax the check here:

cudf/cpp/src/utilities/type_checks.cpp

Lines 66 to 70 in 84ac1d5

	bool column_types_equal(column_view const& lhs, column_view const& rhs)
	{
	if (lhs.type() != rhs.type()) { return false; }
	return type_dispatcher(lhs.type(), columns_equal_fn{}, lhs, rhs);
	}

To only check the type id by changing the if-statement there to:

if (lhs.type().id() != rhs.type().id()) { return false; }

EDIT: Looks like that causes another test to fail at ColumnTypeCheckTest.DifferentFixedWidth so it looks like this fix will need to be further up the chain where this is called. Perhaps a new utility like this is needed:

bool column_types_comparable(column_view const& lhs, column_view const& rhs)
{
  if (lhs.type().id() != rhs.type().id()) { return false; }
  return type_dispatcher(lhs.type(), columns_equal_fn{}, lhs, rhs);
}

Then the check_shape_compatibility in row_operators.cu should be changed to call this new function.
Maybe there is a better word than comparable here.

[davidwendt]

Nice.

[divyegala]

/merge