clang 19.0.0git
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1//===- DataflowAnalysis.h ---------------------------------------*- C++ -*-===//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
9// This file defines base types and functions for building dataflow analyses
10// that run over Control-Flow Graphs (CFGs).
17#include <iterator>
18#include <optional>
19#include <type_traits>
20#include <utility>
21#include <vector>
24#include "clang/Analysis/CFG.h"
31#include "llvm/ADT/STLExtras.h"
32#include "llvm/ADT/STLFunctionalExtras.h"
33#include "llvm/ADT/SmallVector.h"
34#include "llvm/Support/Errc.h"
35#include "llvm/Support/Error.h"
37namespace clang {
38namespace dataflow {
40/// Base class template for dataflow analyses built on a single lattice type.
42/// Requirements:
44/// `Derived` must be derived from a specialization of this class template and
45/// must provide the following public members:
46/// * `LatticeT initialElement()` - returns a lattice element that models the
47/// initial state of a basic block;
48/// * `void transfer(const CFGElement &, LatticeT &, Environment &)` - applies
49/// the analysis transfer function for a given CFG element and lattice
50/// element.
52/// `Derived` can optionally provide the following members:
53/// * `void transferBranch(bool Branch, const Stmt *Stmt, TypeErasedLattice &E,
54/// Environment &Env)` - applies the analysis transfer
55/// function for a given edge from a CFG block of a conditional statement.
57/// `Derived` can optionally override the virtual functions in the
58/// `Environment::ValueModel` interface (which is an indirect base class of
59/// this class).
61/// `LatticeT` is a bounded join-semilattice that is used by `Derived` and must
62/// provide the following public members:
63/// * `LatticeJoinEffect join(const LatticeT &)` - joins the object and the
64/// argument by computing their least upper bound, modifies the object if
65/// necessary, and returns an effect indicating whether any changes were
66/// made to it;
67/// FIXME: make it `static LatticeT join(const LatticeT&, const LatticeT&)`
68/// * `bool operator==(const LatticeT &) const` - returns true if and only if
69/// the object is equal to the argument.
71/// `LatticeT` can optionally provide the following members:
72/// * `LatticeJoinEffect widen(const LatticeT &Previous)` - replaces the
73/// lattice element with an approximation that can reach a fixed point more
74/// quickly than iterated application of the transfer function alone. The
75/// previous value is provided to inform the choice of widened value. The
76/// function must also serve as a comparison operation, by indicating whether
77/// the widened value is equivalent to the previous value with the returned
78/// `LatticeJoinEffect`.
79template <typename Derived, typename LatticeT>
82 /// Bounded join-semilattice that is used in the analysis.
83 using Lattice = LatticeT;
85 explicit DataflowAnalysis(ASTContext &Context) : Context(Context) {}
87 explicit DataflowAnalysis(ASTContext &Context,
89 : TypeErasedDataflowAnalysis(Options), Context(Context) {}
91 ASTContext &getASTContext() final { return Context; }
94 return {static_cast<Derived *>(this)->initialElement()};
95 }
98 const TypeErasedLattice &E2) final {
99 // FIXME: change the signature of join() to avoid copying here.
100 Lattice L1 = llvm::any_cast<const Lattice &>(E1.Value);
101 const Lattice &L2 = llvm::any_cast<const Lattice &>(E2.Value);
102 L1.join(L2);
103 return {std::move(L1)};
104 }
107 const TypeErasedLattice &Previous) final {
108 Lattice &C = llvm::any_cast<Lattice &>(Current.Value);
109 const Lattice &P = llvm::any_cast<const Lattice &>(Previous.Value);
110 return widenInternal(Rank0{}, C, P);
111 }
114 const TypeErasedLattice &E2) final {
115 const Lattice &L1 = llvm::any_cast<const Lattice &>(E1.Value);
116 const Lattice &L2 = llvm::any_cast<const Lattice &>(E2.Value);
117 return L1 == L2;
118 }
121 Environment &Env) final {
122 Lattice &L = llvm::any_cast<Lattice &>(E.Value);
123 static_cast<Derived *>(this)->transfer(Element, L, Env);
124 }
126 void transferBranchTypeErased(bool Branch, const Stmt *Stmt,
127 TypeErasedLattice &E, Environment &Env) final {
128 transferBranchInternal(Rank0{}, *static_cast<Derived *>(this), Branch, Stmt,
129 E, Env);
130 }
133 // These `Rank` structs are used for template metaprogramming to choose
134 // between overloads.
135 struct Rank1 {};
136 struct Rank0 : Rank1 {};
138 // The first-choice implementation: use `widen` when it is available.
139 template <typename T>
140 static auto widenInternal(Rank0, T &Current, const T &Prev)
141 -> decltype(Current.widen(Prev)) {
142 return Current.widen(Prev);
143 }
145 // The second-choice implementation: `widen` is unavailable. Widening is
146 // merged with equality checking, so when widening is unimplemented, we
147 // default to equality checking.
148 static LatticeJoinEffect widenInternal(Rank1, const Lattice &Current,
149 const Lattice &Prev) {
150 return Prev == Current ? LatticeJoinEffect::Unchanged
152 }
154 // The first-choice implementation: `transferBranch` is implemented.
155 template <typename Analysis>
156 static auto transferBranchInternal(Rank0, Analysis &A, bool Branch,
157 const Stmt *Stmt, TypeErasedLattice &L,
158 Environment &Env)
159 -> std::void_t<decltype(A.transferBranch(
160 Branch, Stmt, std::declval<LatticeT &>(), Env))> {
161 A.transferBranch(Branch, Stmt, llvm::any_cast<Lattice &>(L.Value), Env);
162 }
164 // The second-choice implementation: `transferBranch` is unimplemented. No-op.
165 template <typename Analysis>
166 static void transferBranchInternal(Rank1, Analysis &A, bool, const Stmt *,
167 TypeErasedLattice &, Environment &) {}
169 ASTContext &Context;
172// Model of the program at a given program point.
173template <typename LatticeT> struct DataflowAnalysisState {
174 // Model of a program property.
175 LatticeT Lattice;
177 // Model of the state of the program (store and heap).
181/// Performs dataflow analysis and returns a mapping from basic block IDs to
182/// dataflow analysis states that model the respective basic blocks. The
183/// returned vector, if any, will have the same size as the number of CFG
184/// blocks, with indices corresponding to basic block IDs. Returns an error if
185/// the dataflow analysis cannot be performed successfully. Otherwise, calls
186/// `PostVisitCFG` on each CFG element with the final analysis results at that
187/// program point.
189/// `MaxBlockVisits` caps the number of block visits during analysis. See
190/// `runTypeErasedDataflowAnalysis` for a full description. The default value is
191/// essentially arbitrary -- large enough to accommodate what seems like any
192/// reasonable CFG, but still small enough to limit the cost of hitting the
193/// limit.
194template <typename AnalysisT>
196 std::optional<DataflowAnalysisState<typename AnalysisT::Lattice>>>>
198 const AdornedCFG &ACFG, AnalysisT &Analysis, const Environment &InitEnv,
199 std::function<void(const CFGElement &, const DataflowAnalysisState<
200 typename AnalysisT::Lattice> &)>
201 PostVisitCFG = nullptr,
202 std::int32_t MaxBlockVisits = 20'000) {
203 std::function<void(const CFGElement &,
205 PostVisitCFGClosure = nullptr;
206 if (PostVisitCFG) {
207 PostVisitCFGClosure = [&PostVisitCFG](
208 const CFGElement &Element,
209 const TypeErasedDataflowAnalysisState &State) {
210 auto *Lattice =
211 llvm::any_cast<typename AnalysisT::Lattice>(&State.Lattice.Value);
212 // FIXME: we should not be copying the environment here!
213 // Ultimately the PostVisitCFG only gets a const reference anyway.
215 *Lattice, State.Env.fork()});
216 };
217 }
219 auto TypeErasedBlockStates = runTypeErasedDataflowAnalysis(
220 ACFG, Analysis, InitEnv, PostVisitCFGClosure, MaxBlockVisits);
221 if (!TypeErasedBlockStates)
222 return TypeErasedBlockStates.takeError();
224 std::vector<std::optional<DataflowAnalysisState<typename AnalysisT::Lattice>>>
226 BlockStates.reserve(TypeErasedBlockStates->size());
228 llvm::transform(
229 std::move(*TypeErasedBlockStates), std::back_inserter(BlockStates),
230 [](auto &OptState) {
231 return llvm::transformOptional(
232 std::move(OptState), [](TypeErasedDataflowAnalysisState &&State) {
234 llvm::any_cast<typename AnalysisT::Lattice>(
235 std::move(State.Lattice.Value)),
236 std::move(State.Env)};
237 });
238 });
239 return std::move(BlockStates);
242// Create an analysis class that is derived from `DataflowAnalysis`. This is an
243// SFINAE adapter that allows us to call two different variants of constructor
244// (either with or without the optional `Environment` parameter).
245// FIXME: Make all classes derived from `DataflowAnalysis` take an `Environment`
246// parameter in their constructor so that we can get rid of this abomination.
247template <typename AnalysisT>
249 -> decltype(AnalysisT(ASTCtx, Env)) {
250 return AnalysisT(ASTCtx, Env);
252template <typename AnalysisT>
253auto createAnalysis(ASTContext &ASTCtx, Environment &Env)
254 -> decltype(AnalysisT(ASTCtx)) {
255 return AnalysisT(ASTCtx);
258/// Runs a dataflow analysis over the given function and then runs `Diagnoser`
259/// over the results. Returns a list of diagnostics for `FuncDecl` or an
260/// error. Currently, errors can occur (at least) because the analysis requires
261/// too many iterations over the CFG or the SAT solver times out.
263/// The default value of `MaxSATIterations` was chosen based on the following
264/// observations:
265/// - Non-pathological calls to the solver typically require only a few hundred
266/// iterations.
267/// - This limit is still low enough to keep runtimes acceptable (on typical
268/// machines) in cases where we hit the limit.
270/// `MaxBlockVisits` caps the number of block visits during analysis. See
271/// `runDataflowAnalysis` for a full description and explanation of the default
272/// value.
273template <typename AnalysisT, typename Diagnostic>
275 const FunctionDecl &FuncDecl, ASTContext &ASTCtx,
276 llvm::function_ref<llvm::SmallVector<Diagnostic>(
277 const CFGElement &, ASTContext &,
279 Diagnoser,
280 std::int64_t MaxSATIterations = 1'000'000'000,
281 std::int32_t MaxBlockVisits = 20'000) {
283 if (!Context)
284 return Context.takeError();
286 auto Solver = std::make_unique<WatchedLiteralsSolver>(MaxSATIterations);
287 DataflowAnalysisContext AnalysisContext(*Solver);
288 Environment Env(AnalysisContext, FuncDecl);
289 AnalysisT Analysis = createAnalysis<AnalysisT>(ASTCtx, Env);
291 if (llvm::Error Err =
293 *Context, Analysis, Env,
294 [&ASTCtx, &Diagnoser, &Diagnostics](
295 const CFGElement &Elt,
296 const TypeErasedDataflowAnalysisState &State) mutable {
297 auto EltDiagnostics = Diagnoser(
298 Elt, ASTCtx,
300 llvm::any_cast<const typename AnalysisT::Lattice &>(
301 State.Lattice.Value),
302 State.Env));
303 llvm::move(EltDiagnostics, std::back_inserter(Diagnostics));
304 },
305 MaxBlockVisits)
306 .takeError())
307 return std::move(Err);
309 if (Solver->reachedLimit())
310 return llvm::createStringError(llvm::errc::interrupted,
311 "SAT solver timed out");
313 return Diagnostics;
316/// Abstract base class for dataflow "models": reusable analysis components that
317/// model a particular aspect of program semantics in the `Environment`. For
318/// example, a model may capture a type and its related functions.
321 /// Return value indicates whether the model processed the `Element`.
322 virtual bool transfer(const CFGElement &Element, Environment &Env) = 0;
325} // namespace dataflow
326} // namespace clang
Defines the clang::ASTContext interface.
StringRef P
const Environment & Env
Definition: HTMLLogger.cpp:148
llvm::ArrayRef< std::optional< TypeErasedDataflowAnalysisState > > BlockStates
Stores the state of a CFG block if it has been evaluated by the analysis.
const Environment & InitEnv
Initial state to start the analysis.
TypeErasedDataflowAnalysis & Analysis
The analysis to be run.
StateNode * Previous
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:182
Represents a top-level expression in a basic block.
Definition: CFG.h:55
Represents a function declaration or definition.
Definition: Decl.h:1971
Stmt - This represents one statement.
Definition: Stmt.h:84
Holds CFG with additional information derived from it that is needed to perform dataflow analysis.
Definition: AdornedCFG.h:32
static llvm::Expected< AdornedCFG > build(const FunctionDecl &Func)
Builds an AdornedCFG from a FunctionDecl.
Definition: AdornedCFG.cpp:129
Owns objects that encompass the state of a program and stores context that is used during dataflow an...
Base class template for dataflow analyses built on a single lattice type.
LatticeJoinEffect widenTypeErased(TypeErasedLattice &Current, const TypeErasedLattice &Previous) final
Chooses a lattice element that approximates the current element at a program point,...
ASTContext & getASTContext() final
Returns the ASTContext that is used by the analysis.
DataflowAnalysis(ASTContext &Context, DataflowAnalysisOptions Options)
bool isEqualTypeErased(const TypeErasedLattice &E1, const TypeErasedLattice &E2) final
Returns true if and only if the two given type-erased lattice elements are equal.
DataflowAnalysis(ASTContext &Context)
TypeErasedLattice joinTypeErased(const TypeErasedLattice &E1, const TypeErasedLattice &E2) final
Joins two type-erased lattice elements by computing their least upper bound.
void transferBranchTypeErased(bool Branch, const Stmt *Stmt, TypeErasedLattice &E, Environment &Env) final
Applies the analysis transfer function for a given edge from a CFG block of a conditional statement.
TypeErasedLattice typeErasedInitialElement() final
Returns a type-erased lattice element that models the initial state of a basic block.
LatticeT Lattice
Bounded join-semilattice that is used in the analysis.
void transferTypeErased(const CFGElement &Element, TypeErasedLattice &E, Environment &Env) final
Applies the analysis transfer function for a given control flow graph element and type-erased lattice...
Abstract base class for dataflow "models": reusable analysis components that model a particular aspec...
virtual bool transfer(const CFGElement &Element, Environment &Env)=0
Return value indicates whether the model processed the Element.
Supplements Environment with non-standard comparison and join operations.
Holds the state of the program (store and heap) at a given program point.
An interface for a SAT solver that can be used by dataflow analyses.
Definition: Solver.h:28
virtual bool reachedLimit() const =0
Type-erased base class for dataflow analyses built on a single lattice type.
llvm::Expected< llvm::SmallVector< Diagnostic > > diagnoseFunction(const FunctionDecl &FuncDecl, ASTContext &ASTCtx, llvm::function_ref< llvm::SmallVector< Diagnostic >(const CFGElement &, ASTContext &, const TransferStateForDiagnostics< typename AnalysisT::Lattice > &)> Diagnoser, std::int64_t MaxSATIterations=1 '000 '000 '000, std::int32_t MaxBlockVisits=20 '000)
Runs a dataflow analysis over the given function and then runs Diagnoser over the results.
void transfer(const StmtToEnvMap &StmtToEnv, const Stmt &S, Environment &Env, Environment::ValueModel &Model)
Evaluates S and updates Env accordingly.
Definition: Transfer.cpp:865
llvm::Expected< std::vector< std::optional< DataflowAnalysisState< typename AnalysisT::Lattice > > > > runDataflowAnalysis(const AdornedCFG &ACFG, AnalysisT &Analysis, const Environment &InitEnv, std::function< void(const CFGElement &, const DataflowAnalysisState< typename AnalysisT::Lattice > &)> PostVisitCFG=nullptr, std::int32_t MaxBlockVisits=20 '000)
Performs dataflow analysis and returns a mapping from basic block IDs to dataflow analysis states tha...
llvm::Expected< std::vector< std::optional< TypeErasedDataflowAnalysisState > > > runTypeErasedDataflowAnalysis(const AdornedCFG &ACFG, TypeErasedDataflowAnalysis &Analysis, const Environment &InitEnv, std::function< void(const CFGElement &, const TypeErasedDataflowAnalysisState &)> PostVisitCFG, std::int32_t MaxBlockVisits)
Performs dataflow analysis and returns a mapping from basic block IDs to dataflow analysis states tha...
LatticeEffect LatticeJoinEffect
auto createAnalysis(ASTContext &ASTCtx, Environment &Env) -> decltype(AnalysisT(ASTCtx, Env))
Effect indicating whether a lattice operation resulted in a new value.
The JSON file list parser is used to communicate input to InstallAPI.
const FunctionProtoType * T
A read-only version of TransferState.
Definition: MatchSwitch.h:55
Type-erased model of the program at a given program point.
Type-erased lattice element container.