This fixes a subtle issue, described in the comment starting with
"Clone the op without the regions and inline the regions from the old op",
which prevented this conversion from working on non-trivial examples.
Differential Revision: https://reviews.llvm.org/D90203
A "structural" type conversion is one where the underlying ops are
completely agnostic to the actual types involved and simply need to update
their types. An example of this is scf.if -- the scf.if op and the
corresponding scf.yield ops need to update their types accordingly to the
TypeConverter, but otherwise don't care what type conversions are happening.
To test the structural type conversions, it is convenient to define a
bufferize pass for a dialect, which exercises them nicely.
Differential Revision: https://reviews.llvm.org/D89757
