Vsd cross representation evaluation #4
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Reduce number of special cases, and generalise expression evaluation. Special case for ID_plus no longer needed, as a+b+c is still evaluated correctly. Previously incorrectly evaluated expressions such as a*b*c now also evaluated properly.
Without this all operations return top, which is unhelpful. With this change, simple arithmetic starts to work, unary operations, etc. Still more to for multi-value sets.
…behaviour was an error
expression_transform correctly creates all combinations of operands, but
passed the unmodified expression down for further evaluation. If the
expression was something like
2 + p
then at the next stage down, we'd look up symbol 'p' and be handed back
a value set. The evaluated would then try to convert that value set to a
constant which would, naturally, fail. Consequently, the expression
would evaluate to top.
Now, we rewrite the expression in terms of the evaluated operands. If
expression was 2 + p, and p was the set { 2, 3 } the expression is
rewritten first as 2 + 2, then as 2 + 3, which we can gather up into our
result of { 4, 5 }.
The various regression tests in this commit exercise various
combinations of constants and value-sets, value-sets of different size,
and so on. All the tests use addition, but the operator is immaterial.
Splendid side-effect of the expression_transform work :)
Do this by ensuring new object we return are created though the factory, rather than instantiated directly. Several regression tests need updating as a consequence of this change, generally tweaking the regex to allow the context info in place of a hard line end.
Reduce duplication, separated object create from the context object that may wrap it.
I'm not super thrilled about how I've done this, because ideally all object creation should go through the object factory. However, in this particular case a large value set could be converted to an interval. If we hand off to the factory it'll just create another value-set, so we need to explicitly create the interval. However, when we do that we don't have the context wrapper (write location or data dependency). Consequently, I've added variable_sensitivity_object_factoryt::wrap_with_context and exposed it through abstract_environment so we can add the appropriate context wrapper should we need it.
Tidy up evaluate_conditional and pull out evaluate_unary_expr
…factory Default arguments on a virtual function aren't safe. Even through this function isn't overriden anywhere now, it's a latent bug waiting for the future.
Avoid shadowing member variable, make single-arg constructor explicit
value=-set ordering is unstable in the face of code changes, which made tests fragile. Sorting output fixes that and is also easier on the human eye too. We're sorting string representations, so the output isn't a true numerical sort but it's good enough.
This is going to fail in several different ways, but hopefully not for too long
Pull across functions from value_set_abstract_object and value_set_pointer_abstract_object
Point to a constant, dereference, assert we got the same value out --vsd-pointers value-set fails in this commit
Dereferencing no longer causes an abort. It's still not correct, but it's not as wrong.
Using intervals. Value-sets should work but needs more work on value-set value equality.
Writing through a value-set pointer currently does nothing, so test fails.
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The index_ranget has, by C++ standards, an unusual interface more akin to something you'd get on a C# enumerator. This is the first step to making it more container-like, with begin()/end() member functions returning iterators. With this commit, the iterators are input-iterator like, in that they can only be traversed once.
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index_ranget is now only returns its begin and end iterators. It's now returned as a value, rather than through a shared_ptr, as its lifetime will naturally be scope limited and, as described below, polymorphic behaviour is hidden inside. This makes is more natural to use too, as we can just write for (const auto &index : range) rather than having to dereference it. It can now be repeated iterated, rather than the one and done it was in the previous commit. Behind it, the classes that do the actual work of enumerating the ranges have been split out from input_ranget. There is no longer any need to shared these objects, so they are instantiated using unique_ptr rather than shared_ptr.
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Work on operations across different value representations.
Initially, work on merging value-sets and constants.