The fact manager maintains an equivalence relation on data descriptors
that tracks when one data descriptor could be used in place of
another. An algorithm to compute the closure of such facts allows
deducing new synonym facts from existing facts. E.g., for two 2D
vectors u and v it is known that u.x is synonymous with v.x and u.y is
synonymous with v.y, it can be deduced that u and v are synonymous.
The closure computation algorithm is very expensive if we get large
equivalence relations.
This change addresses this in three ways:
- The size of equivalence relations is reduced by limiting the extent
to which the components of a composite are recursively noted as
being equivalent, so that when we have large synonymous arrays we do
not record all array elements as being pairwise equivalent.
- When computing the closure of facts, equivalence classes above a
certain size are simply skipped (which can lead to missed facts)
- The closure computation is performed less frequently - it is invoked
explicitly before fuzzer passes that will benefit from data synonym
facts. A new transformation is used to control its invocation, so
that fuzzing and replaying do not get out of sync.
The change also tidies up the order in which some getters are declared
in FuzzerContext.
Some transformations (e.g. TransformationAddFunction) rely on running
the validator to decide whether the transformation is applicable. A
recent change allowed spirv-fuzz to take validator options, to cater
for the case where a module should be considered valid under
particular conditions. However, validation during the checking of
transformations had no access to these validator options.
This change introduced TransformationContext, which currently consists
of a fact manager and a set of validator options, but could in the
future have other fields corresponding to other objects that it is
useful to have access to when applying transformations. Now, instead
of checking and applying transformations in the context of a
FactManager, a TransformationContext is used. This gives access to
the fact manager as before, and also access to the validator options
when they are needed.
When a data synonym fact about two composites is added, data synonym
facts between all sub-components of the composites are also added.
Furthermore, when data synonym facts been all sub-components of two
composites are known, a data synonym fact relating the two composites
is added. Identification of this case is done in a lazy manner, when
questions about data synonym facts are asked.
The change introduces helper methods to get the size of an array type
and the number of elements of a struct type, and fixes
TransformationCompositeExtract to invalidate analyses appropriately.
This change fixes a bug in EquivalenceRelation, changes the interface
of EquivalenceRelation to avoid exposing (potentially
nondeterministic) unordered sets, and changes the interface of
FactManager to allow querying data synonyms directly. These interface
changes have required a lot of corresponding changes to client code
and tests.
Class TransformationConstructComposite has been renamed to
TransformationCompositeConstruct, to correspond to the name of the
SPIR-V instruction (as is done with e.g. TransformationCopyObject).
Running tests revealed an issue related to checking dominance in
TransformationReplaceIdWithSynonym, which is also fixed here.
