Summary:
In LLVM it is possible for struct constant values to be directly
recursive, with no pointer dereference to close the cycle. These
appear for example as the values of vtables from C++ code.
Currently such recursive records in the Exp and Term languages are
represented as genuinely cyclic values. Compared to a standard term
representation, the presence of cyclic values is a significant
complication everywhere. Since the backend solver does not do anything
such as induction over these, they have to be treated as essentially
atomic.
This patch changes the representation to a standard non-recursive tree
term structure. Instead of cyclic references, an explicit constructor
is added for the "non-tree edges", which simply indicates which
ancestor record value to which the recursive reference points.
There is a potential issue with this representation, since for
mutually recursive records, the representation is not canonical: it
chooses one of the records in the cycle to start from and expresses
the cycles relative to that. Currently the choice of representation is
dictated by the frontend. For the case of vtables, the frontend
translates globals in the same order they appear in the LLVM IR, so
the representation choice is fixed.
It may turn out that other potential uses require more reasoning
support in the backend solver, which would involve a theory of
equality of record values induced by equating the representations
resulting from different rotations of the cycle of records.
Reviewed By: jvillard
Differential Revision: D21441533
fbshipit-source-id: 0c5a11378
Summary:
Having `val size_of : Typ.t -> t` in the signature of `Term` and `val
size_of : t -> t` in the signature of `Exp` gives the impression that
`Term` and `Exp` know something about `Typ`. But they don't, those
functions are only trivial convenience wrappers, and only have a few
uses, so just inline them to clarify that it is `Typ` that knows about
the sizes of types.
Reviewed By: jvillard
Differential Revision: D21441535
fbshipit-source-id: 09b135a8c
Summary:
Move files, adjust build system, etc.
This also separates out the ppx_trace conditional compilation debug
tracing machinery into an independent package and library.
Reviewed By: jvillard
Differential Revision: D20322876
fbshipit-source-id: a50522462
Summary:
`Reg.demangle` is implemented by calling the `_cxa_demangle` C++
runtime system function. This will be linked into the sledge binary,
due to being linked with llvm, but will not necessarily be available
in the sledge library. So make it a dynamically-set function to avoid
calling an undefined function from the library.
Reviewed By: jvillard
Differential Revision: D20323791
fbshipit-source-id: bda9afd37
Summary:
Formulate the canonizer for Extract from Concat terms uniformly as a
concatenation of extracts.
Reviewed By: jvillard
Differential Revision: D20303064
fbshipit-source-id: a45bc45dd
Summary:
Change constructor for solver goals to enforce variable context
conditions, and simplify other context manipulations that are now
unneeded.
Reviewed By: jvillard
Differential Revision: D20248543
fbshipit-source-id: a255c792b
Summary:
In a few places, implicitly witnessed existential variables could
remain in the existential context. This led to weakness in the solver,
where occurrences bound by the existential context would be not known
to be constrained by their witnesses.
Reviewed By: jvillard
Differential Revision: D20248542
fbshipit-source-id: 44f62839c
Summary: In preparation for enforcing invariants in the constructor.
Reviewed By: jvillard
Differential Revision: D20248541
fbshipit-source-id: 41f7d36e5
Summary:
Program (and global) variables are only distinct when considering
their string names, but logical variables need only their ids.
Reviewed By: jvillard
Differential Revision: D20214528
fbshipit-source-id: f7892c3ad
Summary:
When extracting from a concatenation, drop a prefix of the concat with
length equal to the offset of the extraction:
```
(α₀^…^αᵢ^…) [0+n₀+…+nᵢ₋₁, l) ==> (αᵢ^…)[0,l) where nₓ ≡ |αₓ|
```
Reviewed By: jvillard
Differential Revision: D20192874
fbshipit-source-id: cd015aa36
Summary:
Fix unstated assumptions Sh.or_ made on the universal and existential
contexts of disjuncts.
Reviewed By: jvillard
Differential Revision: D20192873
fbshipit-source-id: 945623e57
Summary:
This diff changes `Sh.simplify` from a logically-weakening syntactic
simplification to an equivalence-preserving rewrite. The
implementation is based on `Equality.solve_for_vars` which is also
used by `Solver` to witness existential variables.
Reviewed By: jvillard
Differential Revision: D20120274
fbshipit-source-id: 5e11659ea
Summary:
Just fix accumulated mis-formatting that is swallowed by the
inline-test promotion implementation.
Reviewed By: ngorogiannis
Differential Revision: D20120262
fbshipit-source-id: 0e387dc55
Summary:
Add `Sh.pp_raw` which is closer to the representation, for use when
tracing `Sh` operations.
Reviewed By: ngorogiannis
Differential Revision: D20120281
fbshipit-source-id: e3b1b531a
Summary:
Due to strengthened existential witnessing, the incomplete ad hoc
witness guessing is no longer needed.
Reviewed By: ngorogiannis
Differential Revision: D20120277
fbshipit-source-id: 8ee1656dd
Summary:
Strengthen computation of solution substitutions used for existential
witnessing by using the solver for the memory contents theory. This
uses a generalization of the equation solver implementation which
accepts a predicate used as a filter for equations added to the
solution substitution. When used for solving for a given set of
variables, this filter excludes equations which do not meet the
desired variable conditions.
Reviewed By: jvillard
Differential Revision: D20120275
fbshipit-source-id: 4203d5e41
Summary:
Strengthen existential quantifier witnessing to enable witnessing an
existential with a term containing another existential if no universal
witness is available. Additionally, strengthen existential witnessing
to enable terms of interpreted theories to witness existential
variables.
Also strengthen and simplify the representation invariant checking for
existential witnessing code.
Reviewed By: jvillard
Differential Revision: D20120271
fbshipit-source-id: 4c44fe9ef
Summary:
Handle the case the universal context of a goal does not stay in sync
with that of the minuend.
The need for this indicates that there is some problematic redundancy
in the representation of solver goals.
Reviewed By: ngorogiannis
Differential Revision: D20120268
fbshipit-source-id: 44a4d6260
Summary:
It can happen that canonizing subterms can change the classification
of a term e.g. to the literal true. In such cases, it is not useful or
correct use `Equality.lookup` (which expects to only be used on
uninterpreted applications) to search for some other equation equal to
the literal and use its representative instead.
Reviewed By: ngorogiannis
Differential Revision: D20120279
fbshipit-source-id: 3e2160233
Summary: When equating Concat terms, drop any common prefix or suffix.
Reviewed By: ngorogiannis
Differential Revision: D20120264
fbshipit-source-id: afdeb990e
Summary: No code change, only reordering definitions in prep for later changes.
Reviewed By: ngorogiannis
Differential Revision: D20120263
fbshipit-source-id: b312dfc9a
Summary: Add `Equality.and_term` and replace most of `Sh.pure` with it.
Reviewed By: ngorogiannis
Differential Revision: D20029742
fbshipit-source-id: 07c2f1fe6
Summary:
Replace `Equality.Subst.trim` with `partition_valid` which has a
logical specification (and unsurprisingly fixes some corner case
bugs):
```
val partition_valid : Var.Set.t -> t -> t * Var.Set.t * t
(** Partition ∃xs. σ into equivalent ∃xs. τ ∧ ∃ks. ν where ks and ν
are maximal where ∃ks. ν is universally valid, xs ⊇ ks and ks ∩
fv(τ) = ∅. *)
```
Reviewed By: ngorogiannis
Differential Revision: D20004974
fbshipit-source-id: 5cb3b3835
Summary:
Sh.var_strength determines, in part, if an existential variable has
only a single occurrence. The objective of this is to determine that a
variable is merely a placeholder and not used to express additional
constraints. For this, it suffices to check the weaker condition that
there is a single occurrence in each branch of a DNF expansion.
Reviewed By: ngorogiannis
Differential Revision: D19973779
fbshipit-source-id: 2c90c61f4
Summary:
Currently the free variables of the equality relation of a formula are
contained in the free variables of the rest of the formula, so Sh.fv
ignores them. Propagating equality facts across the star-or structure
of a formula, as necessary for quantifier elimination, breaks this
invariant. Some use cases, such as detecting which variables survive
applying a witness substitution, need to ignore the variables that
appear in the equality relation. This diff adds an argument to
conditionally ignore the variables in the equality relations.
Reviewed By: ngorogiannis
Differential Revision: D19580430
fbshipit-source-id: 2d417d89b
Summary:
In an equation such as `x = ⟨n,a⟩`, `x` is implicitly an aggregate of
size `n` (or else the equation is ill-typed). Make this explicit by
normalizing such equations to e.g. `⟨|⟨n,a⟩|,x⟩ = ⟨n,a⟩`.
Reviewed By: ngorogiannis
Differential Revision: D19358546
fbshipit-source-id: 77f67a0da
Josh Berdine