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|
//===- unittests/Analysis/FlowSensitive/SingelVarConstantPropagation.cpp --===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines a simplistic version of Constant Propagation as an example
// of a forward, monotonic dataflow analysis. The analysis tracks all
// variables in the scope, but lacks escape analysis.
//
//===----------------------------------------------------------------------===//
#include "TestingSupport.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/AST/Expr.h"
#include "clang/AST/Stmt.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/ASTMatchers/ASTMatchers.h"
#include "clang/Analysis/FlowSensitive/DataflowAnalysis.h"
#include "clang/Analysis/FlowSensitive/DataflowEnvironment.h"
#include "clang/Analysis/FlowSensitive/DataflowLattice.h"
#include "clang/Analysis/FlowSensitive/MapLattice.h"
#include "clang/Tooling/Tooling.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/Support/Error.h"
#include "llvm/Testing/Support/Annotations.h"
#include "llvm/Testing/Support/Error.h"
#include "gmock/gmock.h"
#include "gtest/gtest.h"
#include <cstdint>
#include <memory>
#include <ostream>
#include <string>
#include <utility>
namespace clang {
namespace dataflow {
namespace {
using namespace ast_matchers;
// Models the value of an expression at a program point, for all paths through
// the program.
struct ValueLattice {
// FIXME: change the internal representation to use a `std::variant`, once
// clang admits C++17 constructs.
enum class ValueState : bool {
Undefined,
Defined,
};
// `State` determines the meaning of the lattice when `Value` is `None`:
// * `Undefined` -> bottom,
// * `Defined` -> top.
ValueState State;
// When `None`, the lattice is either at top or bottom, based on `State`.
llvm::Optional<int64_t> Value;
constexpr ValueLattice() : State(ValueState::Undefined), Value(llvm::None) {}
constexpr ValueLattice(int64_t V) : State(ValueState::Defined), Value(V) {}
constexpr ValueLattice(ValueState S) : State(S), Value(llvm::None) {}
static constexpr ValueLattice bottom() {
return ValueLattice(ValueState::Undefined);
}
static constexpr ValueLattice top() {
return ValueLattice(ValueState::Defined);
}
friend bool operator==(const ValueLattice &Lhs, const ValueLattice &Rhs) {
return Lhs.State == Rhs.State && Lhs.Value == Rhs.Value;
}
friend bool operator!=(const ValueLattice &Lhs, const ValueLattice &Rhs) {
return !(Lhs == Rhs);
}
LatticeJoinEffect join(const ValueLattice &Other) {
if (*this == Other || Other == bottom() || *this == top())
return LatticeJoinEffect::Unchanged;
if (*this == bottom()) {
*this = Other;
return LatticeJoinEffect::Changed;
}
*this = top();
return LatticeJoinEffect::Changed;
}
};
std::ostream &operator<<(std::ostream &OS, const ValueLattice &L) {
if (L.Value.hasValue())
return OS << *L.Value;
switch (L.State) {
case ValueLattice::ValueState::Undefined:
return OS << "None";
case ValueLattice::ValueState::Defined:
return OS << "Any";
}
llvm_unreachable("unknown ValueState!");
}
using ConstantPropagationLattice = VarMapLattice<ValueLattice>;
constexpr char kDecl[] = "decl";
constexpr char kVar[] = "var";
constexpr char kInit[] = "init";
constexpr char kJustAssignment[] = "just-assignment";
constexpr char kAssignment[] = "assignment";
constexpr char kRHS[] = "rhs";
auto refToVar() { return declRefExpr(to(varDecl().bind(kVar))); }
// N.B. This analysis is deliberately simplistic, leaving out many important
// details needed for a real analysis. Most notably, the transfer function does
// not account for the variable's address possibly escaping, which would
// invalidate the analysis. It also could be optimized to drop out-of-scope
// variables from the map.
class ConstantPropagationAnalysis
: public DataflowAnalysis<ConstantPropagationAnalysis,
ConstantPropagationLattice> {
public:
explicit ConstantPropagationAnalysis(ASTContext &Context)
: DataflowAnalysis<ConstantPropagationAnalysis,
ConstantPropagationLattice>(Context) {}
static ConstantPropagationLattice initialElement() {
return ConstantPropagationLattice::bottom();
}
void transfer(const Stmt *S, ConstantPropagationLattice &Vars,
Environment &Env) {
auto matcher =
stmt(anyOf(declStmt(hasSingleDecl(
varDecl(decl().bind(kVar), hasType(isInteger()),
optionally(hasInitializer(expr().bind(kInit))))
.bind(kDecl))),
binaryOperator(hasOperatorName("="), hasLHS(refToVar()),
hasRHS(expr().bind(kRHS)))
.bind(kJustAssignment),
binaryOperator(isAssignmentOperator(), hasLHS(refToVar()))
.bind(kAssignment)));
ASTContext &Context = getASTContext();
auto Results = match(matcher, *S, Context);
if (Results.empty())
return;
const BoundNodes &Nodes = Results[0];
const auto *Var = Nodes.getNodeAs<clang::VarDecl>(kVar);
assert(Var != nullptr);
if (Nodes.getNodeAs<clang::VarDecl>(kDecl) != nullptr) {
if (const auto *E = Nodes.getNodeAs<clang::Expr>(kInit)) {
Expr::EvalResult R;
Vars[Var] = (E->EvaluateAsInt(R, Context) && R.Val.isInt())
? ValueLattice(R.Val.getInt().getExtValue())
: ValueLattice::top();
} else {
// An unitialized variable holds *some* value, but we don't know what it
// is (it is implementation defined), so we set it to top.
Vars[Var] = ValueLattice::top();
}
} else if (Nodes.getNodeAs<clang::Expr>(kJustAssignment)) {
const auto *E = Nodes.getNodeAs<clang::Expr>(kRHS);
assert(E != nullptr);
Expr::EvalResult R;
Vars[Var] = (E->EvaluateAsInt(R, Context) && R.Val.isInt())
? ValueLattice(R.Val.getInt().getExtValue())
: ValueLattice::top();
} else if (Nodes.getNodeAs<clang::Expr>(kAssignment)) {
// Any assignment involving the expression itself resets the variable to
// "unknown". A more advanced analysis could try to evaluate the compound
// assignment. For example, `x += 0` need not invalidate `x`.
Vars[Var] = ValueLattice::top();
}
}
};
using ::testing::IsEmpty;
using ::testing::Pair;
using ::testing::UnorderedElementsAre;
MATCHER_P(Var, name,
(llvm::Twine(negation ? "isn't" : "is") + " a variable named `" +
name + "`")
.str()) {
return arg->getName() == name;
}
MATCHER_P(HasConstantVal, v, "") {
return arg.Value.hasValue() && *arg.Value == v;
}
MATCHER(Varies, "") { return arg == arg.top(); }
MATCHER_P(HoldsCPLattice, m,
((negation ? "doesn't hold" : "holds") +
llvm::StringRef(" a lattice element that ") +
::testing::DescribeMatcher<ConstantPropagationLattice>(m, negation))
.str()) {
return ExplainMatchResult(m, arg.Lattice, result_listener);
}
class MultiVarConstantPropagationTest : public ::testing::Test {
protected:
template <typename Matcher>
void RunDataflow(llvm::StringRef Code, Matcher Expectations) {
ASSERT_THAT_ERROR(
test::checkDataflow<ConstantPropagationAnalysis>(
Code, "fun",
[](ASTContext &C, Environment &) {
return ConstantPropagationAnalysis(C);
},
[&Expectations](
llvm::ArrayRef<std::pair<
std::string, DataflowAnalysisState<
ConstantPropagationAnalysis::Lattice>>>
Results,
ASTContext &) { EXPECT_THAT(Results, Expectations); },
{"-fsyntax-only", "-std=c++17"}),
llvm::Succeeded());
}
};
TEST_F(MultiVarConstantPropagationTest, JustInit) {
std::string Code = R"(
void fun() {
int target = 1;
// [[p]]
}
)";
RunDataflow(Code, UnorderedElementsAre(
Pair("p", HoldsCPLattice(UnorderedElementsAre(Pair(
Var("target"), HasConstantVal(1)))))));
}
TEST_F(MultiVarConstantPropagationTest, Assignment) {
std::string Code = R"(
void fun() {
int target = 1;
// [[p1]]
target = 2;
// [[p2]]
}
)";
RunDataflow(Code, UnorderedElementsAre(
Pair("p1", HoldsCPLattice(UnorderedElementsAre(Pair(
Var("target"), HasConstantVal(1))))),
Pair("p2", HoldsCPLattice(UnorderedElementsAre(Pair(
Var("target"), HasConstantVal(2)))))));
}
TEST_F(MultiVarConstantPropagationTest, AssignmentCall) {
std::string Code = R"(
int g();
void fun() {
int target;
target = g();
// [[p]]
}
)";
RunDataflow(Code, UnorderedElementsAre(
Pair("p", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), Varies()))))));
}
TEST_F(MultiVarConstantPropagationTest, AssignmentBinOp) {
std::string Code = R"(
void fun() {
int target;
target = 2 + 3;
// [[p]]
}
)";
RunDataflow(Code, UnorderedElementsAre(
Pair("p", HoldsCPLattice(UnorderedElementsAre(Pair(
Var("target"), HasConstantVal(5)))))));
}
TEST_F(MultiVarConstantPropagationTest, PlusAssignment) {
std::string Code = R"(
void fun() {
int target = 1;
// [[p1]]
target += 2;
// [[p2]]
}
)";
RunDataflow(Code, UnorderedElementsAre(
Pair("p1", HoldsCPLattice(UnorderedElementsAre(Pair(
Var("target"), HasConstantVal(1))))),
Pair("p2", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), Varies()))))));
}
TEST_F(MultiVarConstantPropagationTest, SameAssignmentInBranches) {
std::string Code = R"cc(
void fun(bool b) {
int target;
// [[p1]]
if (b) {
target = 2;
// [[pT]]
} else {
target = 2;
// [[pF]]
}
(void)0;
// [[p2]]
}
)cc";
RunDataflow(Code,
UnorderedElementsAre(
Pair("p1", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), Varies())))),
Pair("pT", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), HasConstantVal(2))))),
Pair("pF", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), HasConstantVal(2))))),
Pair("p2", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), HasConstantVal(2)))))));
}
// Verifies that the analysis tracks multiple variables simultaneously.
TEST_F(MultiVarConstantPropagationTest, TwoVariables) {
std::string Code = R"(
void fun() {
int target = 1;
// [[p1]]
int other = 2;
// [[p2]]
target = 3;
// [[p3]]
}
)";
RunDataflow(Code,
UnorderedElementsAre(
Pair("p1", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), HasConstantVal(1))))),
Pair("p2", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), HasConstantVal(1)),
Pair(Var("other"), HasConstantVal(2))))),
Pair("p3", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), HasConstantVal(3)),
Pair(Var("other"), HasConstantVal(2)))))));
}
TEST_F(MultiVarConstantPropagationTest, TwoVariablesInBranches) {
std::string Code = R"cc(
void fun(bool b) {
int target;
int other;
// [[p1]]
if (b) {
target = 2;
// [[pT]]
} else {
other = 3;
// [[pF]]
}
(void)0;
// [[p2]]
}
)cc";
RunDataflow(Code, UnorderedElementsAre(
Pair("p1", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), Varies()),
Pair(Var("other"), Varies())))),
Pair("pT", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), HasConstantVal(2)),
Pair(Var("other"), Varies())))),
Pair("pF", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("other"), HasConstantVal(3)),
Pair(Var("target"), Varies())))),
Pair("p2", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), Varies()),
Pair(Var("other"), Varies()))))));
}
TEST_F(MultiVarConstantPropagationTest, SameAssignmentInBranch) {
std::string Code = R"cc(
void fun(bool b) {
int target = 1;
// [[p1]]
if (b) {
target = 1;
}
(void)0;
// [[p2]]
}
)cc";
RunDataflow(Code, UnorderedElementsAre(
Pair("p1", HoldsCPLattice(UnorderedElementsAre(Pair(
Var("target"), HasConstantVal(1))))),
Pair("p2", HoldsCPLattice(UnorderedElementsAre(Pair(
Var("target"), HasConstantVal(1)))))));
}
TEST_F(MultiVarConstantPropagationTest, NewVarInBranch) {
std::string Code = R"cc(
void fun(bool b) {
if (b) {
int target;
// [[p1]]
target = 1;
// [[p2]]
} else {
int target;
// [[p3]]
target = 1;
// [[p4]]
}
}
)cc";
RunDataflow(Code, UnorderedElementsAre(
Pair("p1", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), Varies())))),
Pair("p2", HoldsCPLattice(UnorderedElementsAre(Pair(
Var("target"), HasConstantVal(1))))),
Pair("p3", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), Varies())))),
Pair("p4", HoldsCPLattice(UnorderedElementsAre(Pair(
Var("target"), HasConstantVal(1)))))));
}
TEST_F(MultiVarConstantPropagationTest, DifferentAssignmentInBranches) {
std::string Code = R"cc(
void fun(bool b) {
int target;
// [[p1]]
if (b) {
target = 1;
// [[pT]]
} else {
target = 2;
// [[pF]]
}
(void)0;
// [[p2]]
}
)cc";
RunDataflow(Code, UnorderedElementsAre(
Pair("p1", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), Varies())))),
Pair("pT", HoldsCPLattice(UnorderedElementsAre(Pair(
Var("target"), HasConstantVal(1))))),
Pair("pF", HoldsCPLattice(UnorderedElementsAre(Pair(
Var("target"), HasConstantVal(2))))),
Pair("p2", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), Varies()))))));
}
TEST_F(MultiVarConstantPropagationTest, DifferentAssignmentInBranch) {
std::string Code = R"cc(
void fun(bool b) {
int target = 1;
// [[p1]]
if (b) {
target = 3;
}
(void)0;
// [[p2]]
}
)cc";
RunDataflow(Code, UnorderedElementsAre(
Pair("p1", HoldsCPLattice(UnorderedElementsAre(Pair(
Var("target"), HasConstantVal(1))))),
Pair("p2", HoldsCPLattice(UnorderedElementsAre(
Pair(Var("target"), Varies()))))));
}
} // namespace
} // namespace dataflow
} // namespace clang
|
