Similar to arguments and results, now we require region definition in ops to
be specified as a DAG expression with the 'region' operator. This way we can
specify the constraints for each region and optionally give the region a name.
Two kinds of region constraints are added, one allowing any region, and the
other requires a certain number of blocks.
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PiperOrigin-RevId: 250790211
Previously we have multiple mechanisms to specify op definition and match constraints:
TypeConstraint, AttributeConstraint, Type, Attr, mAttr, mAttrAnyOf, mPat. These variants
are not added because there are so many distinct cases we need to model; essentially,
they are all carrying a predicate. It's just an artifact of implementation.
It's quite confusing for users to grasp these variants and choose among them. Instead,
as the OpBase TableGen file, we need to strike to provide an unified mechanism. Each
dialect has the flexibility to define its own aliases if wanted.
This CL removes mAttr, mAttrAnyOf, mPat. A new base class, Constraint, is added. Now
TypeConstraint and AttrConstraint derive from Constraint. Type and Attr further derive
from TypeConstraint and AttrConstraint, respectively.
Comments are revised and examples are added to make it clear how to use constraints.
PiperOrigin-RevId: 240125076
Lei Zhang