PatternTransformation._pipeline_results only set during calls to apply().

[philip-paul-mueller]

Because PatternTransformation, i.e. most of the data flow transformations, including MapFusion are called through the apply() function, that lacks the pipeline_results argument that apply_pass() has.
To make this argument available to such passes, PatternTransformation has this member _pipeline_results, that is set to the value of pipeline_results argument that was passed to the apply_pass() method.
However, this member is only set during the execution of apply(), but when can_be_applied() is run the value is None.

I do not see a reason why it has to be that way and would propose to change this, such that _pipeline_results is also set during can_be_applied().