Nested soft constraint support #178
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Separate soft from hard constraints while building RandInfo. Do this by building up a stack of the conditions behind each 'if/else/then' and 'implies' scope and generate an 'implies' on the 'and' of those conditions for each soft constraint. Also remove the soft constraint from those constraint_l after doing so.
Now that nested soft constraints are recreated as individual, soft constraints the hard constraint building needs to skip them and soft constraints need to be built with the soft flag enabled. This happens both in the rand_set_node_builder and back in randomizer when it constructs the list of python and Boolector constraint tuples. The randomizer call should be picking up cached objects, but still needs the flag to not return None for the object. Unless there's a different way to do so?
When randsets combine they were call add_constraint on nested soft constraints that had been added using add_soft_constraint to bypass the ConstraintSoftModel check. Since the 'priority' attribute was already being added to the base constraint in nested constraints to make sorting soft constraints possible, I changed the add_constraint check to test for that as well and removed the add_soft_constraint function.
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@mballance The wording in the docs mentions soft constraints being limited to expressions and nothing about nested constraints not working, so I don't think the docs need to be updated. Unless an example of nested soft constraints would be useful in the docs, then I could add something relevant.
I'm not sure about the inline constraint bit. Inline constraints are randomize_with constraints, correct? I ran a test on master and the soft constraint still shows up in the debug print and appears to be constraining as expected. I don't recall what SV does here either, although I guess most of the time you would want hard constraints in that scenario. |
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@alwilson, this looks great! I'm happy with the implementation, and it looks like all relevant corner cases are covered. |
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@mballance Thanks! Glad to contribute. I'm okay with my username / name (Alex Wilson) being listed in the ChangeLog file. |
This addresses #176 by first separating each soft constraint into its own Implies soft constraint while building RandInfo. The condition for the Implies constraint is built up by keeping a stack of the if_then and implies conditions while visiting constraints and combining those with And expressions.
Then in the RandSetNodeBuilder a soft_phase flag has been added to prevent nested soft constraints from being built during the hard constraints. A new soft constraints build phase is added to specifically build soft and nested soft constraints.
There's a TODO in rand_info_builder.py under visit_constraint_soft about how a 'priority' attribute is being added to the Implies constraint built up for nested soft constraints so that they can be sorted alongside other soft constraints as well as make it possible
to check for soft vs hard constraints in the add_constraints function.
I should reread the docs, but the soft constraints section might need to be changed.