When a `nullptr` is assigned to a pointer variable, it is wrapped in a `ImplicitCastExpr` with cast kind `CK_NullTo(Member)Pointer`. This patch assigns singleton pointer values representing null to these expressions.
For each pointee type, a singleton null `PointerValue` is created and stored in the `NullPointerVals` map of the `DataflowAnalysisContext` class. The pointee type is retrieved from the implicit cast expression, and used to initialise the `PointeeLoc` field of the `PointerValue`. The `PointeeLoc` created is not mapped to any `Value`, reflecting the absence of value indicated by null pointers.
Reviewed By: gribozavr2, sgatev, xazax.hun
Differential Revision: https://reviews.llvm.org/D128056
`createStorageLocation` in `DataflowEnvironment` is now a trivial wrapper around the logic in `DataflowAnalysisContext`.
Additionally, `getObjectFields` and `getFieldsFromClassHierarchy` (required for the implementation of `createStorageLocation`) are also moved to `DataflowAnalysisContext`.
Reviewed By: gribozavr2, sgatev
Differential Revision: https://reviews.llvm.org/D128359
We distinguish between the referent location for `ReferenceValue` and pointee location for `PointerValue`. The former must be non-empty but the latter may be empty in the case of a `nullptr`
Reviewed By: gribozavr2, sgatev
Differential Revision: https://reviews.llvm.org/D127745
This patch precedes a future patch to make PointeeLoc for PointerValue possibly empty (for nullptr), by using a pointer instead of a reference type.
ReferenceValue should maintain a non-empty PointeeLoc reference.
Reviewed By: gribozavr2
Differential Revision: https://reviews.llvm.org/D127312
The API for `AggregateStorageLocation` does not allow for missing fields (it asserts). Therefore, it is incorrect to filter out any fields at location-creation time which may be accessed by the code. Currently, we limit filtering to private, base-calss fields on the assumption that those can never be accessed. However, `friend` declarations can invalidate that assumption, thereby breaking our invariants.
This patch removes said field filtering to avoid violating the invariant of "no missing fields" for `AggregateStorageLocation`.
Differential Revision: https://reviews.llvm.org/D126420
When constructing the `Environment`, the `this` pointee is established
for a `CXXMethodDecl` by looking at its parent. However, inside of
lambdas, a `CXXThisExpr` refers to the captured `this` coming from the
enclosing member function.
When establishing the `this` pointee for a function, we check whether
the function is a lambda, and check for an enclosing member function
to establish the `this` pointee storage location.
Differential Revision: https://reviews.llvm.org/D126413
Ignore `MemberLocToStruct` in environment comparison. As an ancillary data
structure, including it is redundant. We also can generate environments which
differ in their `MemberLocToStruct` but are otherwise equivalent.
Differential Revision: https://reviews.llvm.org/D126314
A follow-up to 62b2a47 to centralize the logic that skips expressions
that the CFG does not emit. This allows client code to avoid
sprinkling this logic everywhere.
Add redirects in the transfer function to similarly skip such
expressions by forwarding the visit to the sub-expression.
Differential Revision: https://reviews.llvm.org/D124965
`IgnoreParenImpCasts` will remove implicit casts to bool
(e.g. `PointerToBoolean`), such that the resulting expression may not
be of the `bool` type. The `cast_or_null<BoolValue>` in
`extendFlowCondition` will then trigger an assert, as the pointer
expression will not have a `BoolValue`.
Instead, we only skip `ExprWithCleanups` and `ParenExpr` nodes, as the
CFG does not emit them.
Differential Revision: https://reviews.llvm.org/D124807
Enable efficient implementation of context-aware joining of distinct
boolean values. It can be used to join distinct boolean values while
preserving flow condition information.
Flow conditions are represented as Token <=> Clause iff formulas. To
perform context-aware joining, one can simply add the tokens of flow
conditions to the formula when joining distinct boolean values, e.g:
`makeOr(makeAnd(FC1, Val1), makeAnd(FC2, Val2))`. This significantly
simplifies the implementation of `Environment::join`.
This patch removes the `DataflowAnalysisContext::getSolver` method.
The `DataflowAnalysisContext::flowConditionImplies` method should be
used instead.
Reviewed-by: ymandel, xazax.hun
Differential Revision: https://reviews.llvm.org/D124395
This patch changes `Environment::join`, in the case that two values at the same
location are not (pointer) equal, to structurally compare indirection values
(pointers and references) for equivalence (that is, equivalent pointees) before
resorting to merging.
This change makes join consistent with equivalence, which also performs
structural comparison. It also fixes a bug where the values are `ReferenceValue`
but the merge creates a non-reference value. This case arises when the
`ReferenceValue`s were created to represent an lvalue, so the "reference-ness"
is not reflected in the type. In this case, the pointees will always be
equivalent, because lvalues at the same code location point to the location of a
fixed declaration, whose location is itself stable across blocks.
We were unable to reproduce a unit test for this latter bug, but have verified
the fix in the context of a larger piece of code that triggers the bug.
Differential Revision: https://reviews.llvm.org/D124540
The current implementation mutates the environment as it performs the
join. However, that interferes with the call to the model's `merge` operation,
which can modify `MergedEnv`. Since any modifications are assumed to apply to
the post-join environment, providing the same environment for both is
incorrect. This mismatch is a particular concern for joining the flow
conditions, where modifications in the old environment may not be propagated to
the new one.
Differential Revision: https://reviews.llvm.org/D124104
Under the hood this prints the same as `QualType::getAsString()` but cuts out the middle-man when that string is sent to another raw_ostream.
Also cleaned up all the call sites where this occurs.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D123926
Currently, when the framework is used with an analysis that does not override
`compareEquivalent`, it does not terminate for most loops. The root cause is the
interaction of (the default implementation of) environment comparison
(`compareEquivalent`) and the means by which locations and values are
allocated. Specifically, the creation of certain values (including: reference
and pointer values; merged values) results in allocations of fresh locations in
the environment. As a result, analysis of even trivial loop bodies produces
different (if isomorphic) environments, on identical inputs. At the same time,
the default analysis relies on strict equality (versus some relaxed notion of
equivalence). Together, when the analysis compares these isomorphic, yet
unequal, environments, to determine whether the successors of the given block
need to be (re)processed, the result is invariably "yes", thus preventing loop
analysis from reaching a fixed point.
There are many possible solutions to this problem, including equivalence that is
less than strict pointer equality (like structural equivalence) and/or the
introduction of an explicit widening operation. However, these solutions will
require care to be implemented correctly. While a high priority, it seems more
urgent that we fix the current default implentation to allow
termination. Therefore, this patch proposes, essentially, to change the default
comparison to trivally equate any two values. As a result, we can say precisely
that the analysis will process the loop exactly twice -- once to establish an
initial result state and the second to produce an updated result which will
(always) compare equal to the previous. While clearly unsound -- we are not
reaching a fix point of the transfer function, in practice, this level of
analysis will find many practical issues where a single iteration of the loop
impacts abstract program state.
Note, however, that the change to the default `merge` operation does not affect
soundness, because the framework already produces a fresh (sound) abstraction of
the value when the two values are distinct. The previous setting was overly
conservative.
Differential Revision: https://reviews.llvm.org/D123586
This patch extends the join logic for environments to explicitly handle
boolean values. It creates the disjunction of both source values, guarded by the
respective flow conditions from each input environment. This change allows the
framework to reason about boolean correlations across multiple branches (and
subsequent joins).
Differential Revision: https://reviews.llvm.org/D122838
Currently, the framework does not track derived class access to base
fields. This patch adds that support and a corresponding test.
Differential Revision: https://reviews.llvm.org/D122273
When pre-initializing fields in the environment, the code assumed that all
fields of a struct would be initialized. However, given limits on value
construction, that assumption is incorrect. This patch changes the code to drop
that assumption and thereby avoid dereferencing a nullptr.
Differential Revision: https://reviews.llvm.org/D121158
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: ymandel, xazax.hun
Differential Revision: https://reviews.llvm.org/D120984
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: ymandel, xazax.hun
Differential Revision: https://reviews.llvm.org/D120711
Adds two new parameters to control the size of data structures modeled in the environment: # of values and depth of data structure. The environment already prevents creation of recursive data structures, but that was insufficient in practice. Very large structs still ground the analysis to a halt. These new parameters allow tuning the size more effectively.
In this patch, the parameters are set as internal constants. We leave to a future patch to make these proper model parameters.
Differential Revision: https://reviews.llvm.org/D120510
When assigning a value to a storage location of a struct member we
need to also update the value in the corresponding `StructValue`.
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: ymandel, xazax.hun
Differential Revision: https://reviews.llvm.org/D120414
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: ymandel, xazax.hun
Differential Revision: https://reviews.llvm.org/D120149
Make specializations of `DataflowAnalysis` extendable with domain-specific
logic for comparing distinct values when comparing environments.
This includes a breaking change to the `runDataflowAnalysis` interface
as the return type is now `llvm::Expected<...>`.
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: ymandel, xazax.hun
Differential Revision: https://reviews.llvm.org/D118596
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: ymandel, xazax.hun
Differential Revision: https://reviews.llvm.org/D118480
Make specializations of `DataflowAnalysis` extendable with domain-specific
logic for merging distinct values when joining environments. This could be
a strict lattice join or a more general widening operation.
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: xazax.hun
Differential Revision: https://reviews.llvm.org/D118038
This patch ensures that the dataflow analysis framework does not crash
when it encounters access to members of union types.
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: xazax.hun
Differential Revision: https://reviews.llvm.org/D118226
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: xazax.hun
Differential Revision: https://reviews.llvm.org/D117754
Since Environment's setValue method already does part of the work that
initValueInStorageLocation does, we can factor out a new createValue
method to reduce the duplication.
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: ymandel, xazax.hun
Differential Revision: https://reviews.llvm.org/D117493
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: ymandel, xazax.hun
Differential Revision: https://reviews.llvm.org/D117218
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: ymandel, xazax.hun
Differential Revision: https://reviews.llvm.org/D117012
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Differential Revision: https://reviews.llvm.org/D116596
This is part of the implementation of the dataflow analysis framework.
See "[RFC] A dataflow analysis framework for Clang AST" on cfe-dev.
Reviewed-by: xazax.hun
Differential Revision: https://reviews.llvm.org/D116368
Wei Yi Tee