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[clang][dataflow] Add an early-out to flowConditionImplies() / flowConditionAllows(). #78172

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Merged
merged 1 commit into from
Jan 16, 2024
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[clang][dataflow] Add an early-out to flowConditionImplies() / flowConditionAllows(). #78172

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4 changes: 4 additions & 0 deletions clang/include/clang/Analysis/FlowSensitive/Formula.h
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Original file line number Diff line number Diff line change
Expand Up @@ -75,6 +75,10 @@ class alignas(const Formula *) Formula {
return static_cast<bool>(Value);
}

bool isLiteral(bool b) const {
return kind() == Literal && static_cast<bool>(Value) == b;
}

ArrayRef<const Formula *> operands() const {
return ArrayRef(reinterpret_cast<Formula *const *>(this + 1),
numOperands(kind()));
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6 changes: 6 additions & 0 deletions clang/lib/Analysis/FlowSensitive/DataflowAnalysisContext.cpp
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Expand Up @@ -174,6 +174,9 @@ Solver::Result DataflowAnalysisContext::querySolver(

bool DataflowAnalysisContext::flowConditionImplies(Atom Token,
const Formula &F) {
if (F.isLiteral(true))
return true;

// Returns true if and only if truth assignment of the flow condition implies
// that `F` is also true. We prove whether or not this property holds by
// reducing the problem to satisfiability checking. In other words, we attempt
Expand All @@ -188,6 +191,9 @@ bool DataflowAnalysisContext::flowConditionImplies(Atom Token,

bool DataflowAnalysisContext::flowConditionAllows(Atom Token,
const Formula &F) {
if (F.isLiteral(false))
return false;

llvm::SetVector<const Formula *> Constraints;
Constraints.insert(&arena().makeAtomRef(Token));
Constraints.insert(&F);
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30 changes: 27 additions & 3 deletions clang/unittests/Analysis/FlowSensitive/DataflowAnalysisContextTest.cpp
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Expand Up @@ -33,10 +33,34 @@ TEST_F(DataflowAnalysisContextTest, DistinctTopsNotEquivalent) {
EXPECT_FALSE(Context.equivalentFormulas(X.formula(), Y.formula()));
}

TEST_F(DataflowAnalysisContextTest, EmptyFlowCondition) {
TEST_F(DataflowAnalysisContextTest, TautologicalFlowConditionImplies) {
Atom FC = A.makeFlowConditionToken();
auto &C = A.makeAtomRef(A.makeAtom());
EXPECT_FALSE(Context.flowConditionImplies(FC, C));
EXPECT_TRUE(Context.flowConditionImplies(FC, A.makeLiteral(true)));
EXPECT_FALSE(Context.flowConditionImplies(FC, A.makeLiteral(false)));
EXPECT_FALSE(Context.flowConditionImplies(FC, A.makeAtomRef(A.makeAtom())));
}

TEST_F(DataflowAnalysisContextTest, TautologicalFlowConditionAllows) {
Atom FC = A.makeFlowConditionToken();
EXPECT_TRUE(Context.flowConditionAllows(FC, A.makeLiteral(true)));
EXPECT_FALSE(Context.flowConditionAllows(FC, A.makeLiteral(false)));
EXPECT_TRUE(Context.flowConditionAllows(FC, A.makeAtomRef(A.makeAtom())));
}

TEST_F(DataflowAnalysisContextTest, ContradictoryFlowConditionImpliesAnything) {
Atom FC = A.makeFlowConditionToken();
Context.addFlowConditionConstraint(FC, A.makeLiteral(false));
EXPECT_TRUE(Context.flowConditionImplies(FC, A.makeLiteral(true)));
EXPECT_TRUE(Context.flowConditionImplies(FC, A.makeLiteral(false)));
EXPECT_TRUE(Context.flowConditionImplies(FC, A.makeAtomRef(A.makeAtom())));
}

TEST_F(DataflowAnalysisContextTest, ContradictoryFlowConditionAllowsNothing) {
Atom FC = A.makeFlowConditionToken();
Context.addFlowConditionConstraint(FC, A.makeLiteral(false));
EXPECT_FALSE(Context.flowConditionAllows(FC, A.makeLiteral(true)));
EXPECT_FALSE(Context.flowConditionAllows(FC, A.makeLiteral(false)));
EXPECT_FALSE(Context.flowConditionAllows(FC, A.makeAtomRef(A.makeAtom())));
}

TEST_F(DataflowAnalysisContextTest, AddFlowConditionConstraint) {
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