To help ensure that optimizations that do less cautious invalidation
of analyses are implemented correctly, this change adds checks to the
tests of various transformations to ensure that analyses such as
def-use are up to date.
This fixes a problem where TransformationInlineFunction could lead to
distinct instructions having identical unique ids. It adds a validity
check to detect this problem in general.
Fixes#3911.
Adds a virtual method, GetFreshIds(), to Transformation. Every
transformation uses this to indicate which ids in its protobuf message
are fresh ids. This means that when replaying a sequence of
transformations the replayer can obtain a smallest id that is not in
use by the module already and that will not be used by any
transformation by necessity. Ids greater than or equal to this id
can be used as overflow ids.
Fixes#3851.
TransformationContext now holds a std::unique_ptr to a FactManager,
rather than a plain pointer. This makes it easier for clients of
TransformationContext to work with heap-allocated instances of
TransformationContext, which is needed in some upcoming work.
This PR changes the fact manager so that, when calling some of the
functions in submanagers, passes references to other submanagers if
necessary (e.g. to make consistency checks).
In particular:
- DataSynonymAndIdEquationFacts is passed to the AddFactIdIsIrrelevant
function of IrrelevantValueFacts
- IrrelevantValueFacts is passed to the AddFact functions of
DataSynonymAndIdEquationFacts
The IRContext is also passed when necessary and the calls to the
corresponding functions in FactManager were updated to be valid and
always use an updated context.
Fixes#3550.
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.
The management of equation facts suffered from two problems:
(1) The processing of an equation fact required the data descriptors
used in the equation to be in canonical form. However, during
fact processing it can be deduced that certain data descriptors
are equivalent, causing their equivalence classes to be merged,
and that could cause previously canonical data descriptors to no
longer be canonical.
(2) Related to this, if id equations were known about a canonical data
descriptor dd1, and other id equations known about a different
canonical data descriptor dd2, the equation facts about these data
descriptors were not being merged in the event that dd1 and dd2
were deduced to be equivalent.
This changes solves (1) by not requiring equation facts to be in
canonical form while processing them, but instead always checking
whether (not necessary canonical) data descriptors are equivalent when
looking for corollaries of equation facts, rather than comparing them
using ==.
Problem (2) is solved by adding logic to merge sets of equations when
data descriptors are made equivalent.
In addition, the change also requires elements to be registered in an
equivalence relation before they can be made equivalent, rather than
being added (if not already present) at the point of being made
equivalent.
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.
This introduces a new fuzzer pass to add instructions to the module
that define equations, and support in the fact manager for recording
equation facts and deducing synonym facts from equation facts.
Initially the only equations that are supported involve OpIAdd,
OpISub, OpSNegate and OpLogicalNot, but there is scope for adding
support for equations over various other operators.
