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[clang][dataflow] Merge RecordValues with different locations correctly. #65319

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Merged
merged 1 commit into from
Sep 12, 2023
Merged

[clang][dataflow] Merge RecordValues with different locations correctly. #65319

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25 changes: 13 additions & 12 deletions clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -125,18 +125,19 @@ static Value *mergeDistinctValues(QualType Type, Value &Val1,

Value *MergedVal = nullptr;
if (auto *RecordVal1 = dyn_cast<RecordValue>(&Val1)) {
[[maybe_unused]] auto *RecordVal2 = cast<RecordValue>(&Val2);

// Values to be merged are always associated with the same location in
// `LocToVal`. The location stored in `RecordVal` should therefore also
// be the same.
assert(&RecordVal1->getLoc() == &RecordVal2->getLoc());

// `RecordVal1` and `RecordVal2` may have different properties associated
// with them. Create a new `RecordValue` without any properties so that we
// soundly approximate both values. If a particular analysis needs to merge
// properties, it should do so in `DataflowAnalysis::merge()`.
MergedVal = &MergedEnv.create<RecordValue>(RecordVal1->getLoc());
auto *RecordVal2 = cast<RecordValue>(&Val2);

if (&RecordVal1->getLoc() == &RecordVal2->getLoc())
// `RecordVal1` and `RecordVal2` may have different properties associated
// with them. Create a new `RecordValue` with the same location but
// without any properties so that we soundly approximate both values. If a
// particular analysis needs to merge properties, it should do so in
// `DataflowAnalysis::merge()`.
MergedVal = &MergedEnv.create<RecordValue>(RecordVal1->getLoc());
else
// If the locations for the two records are different, need to create a
// completely new value.
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Given that how cryptic when this could happen, it might be helpful to have a brief comment that both could happen depending on a subtle order of CFG and therefore how merge happens.

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Not sure exactly what you mean...

Whether the locations are the same or not doesn't really depend on the order in which we process CFG blocks. Instead, locations are guaranteed to be the same if the RecordValue is stored in ExprToLoc, and they are usually (but not always) different if the RecordValue is stored in ExprToVal.

The order in which we process CFG blocks affects whether we actually see different RecordValues or not when the merge happens -- which makes merges difficult to trigger reliably from an integration test (example). But I'm not sure how relevant that is to the situation here?

Anyway, my hope is that all of this will go away relatively soon because we're now working on eliminating the RecordStorageLocation from RecordValue.

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I think you're right, I wanted to see if some comment may help but it's a bit irrelevant here. Also given that it's going away I'm good with it, thanks!

MergedVal = MergedEnv.createValue(Type);
} else {
MergedVal = MergedEnv.createValue(Type);
}
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69 changes: 69 additions & 0 deletions clang/unittests/Analysis/FlowSensitive/DataflowEnvironmentTest.cpp
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Expand Up @@ -96,6 +96,75 @@ TEST_F(EnvironmentTest, CreateValueRecursiveType) {
EXPECT_THAT(PV, NotNull());
}

TEST_F(EnvironmentTest, JoinRecords) {
using namespace ast_matchers;

std::string Code = R"cc(
struct S {};
// Need to use the type somewhere so that the `QualType` gets created;
S s;
)cc";

auto Unit =
tooling::buildASTFromCodeWithArgs(Code, {"-fsyntax-only", "-std=c++11"});
auto &Context = Unit->getASTContext();

ASSERT_EQ(Context.getDiagnostics().getClient()->getNumErrors(), 0U);

auto Results =
match(qualType(hasDeclaration(recordDecl(hasName("S")))).bind("SType"),
Context);
const QualType *TyPtr = selectFirst<QualType>("SType", Results);
ASSERT_THAT(TyPtr, NotNull());
QualType Ty = *TyPtr;
ASSERT_FALSE(Ty.isNull());

auto *ConstructExpr = CXXConstructExpr::CreateEmpty(Context, 0);
ConstructExpr->setType(Ty);
ConstructExpr->setValueKind(VK_PRValue);

// Two different `RecordValue`s with the same location are joined into a
// third `RecordValue` with that same location.
{
Environment Env1(DAContext);
auto &Val1 = *cast<RecordValue>(Env1.createValue(Ty));
RecordStorageLocation &Loc = Val1.getLoc();
Env1.setValue(*ConstructExpr, Val1);

Environment Env2(DAContext);
auto &Val2 = Env2.create<RecordValue>(Loc);
Env2.setValue(Loc, Val2);
Env2.setValue(*ConstructExpr, Val2);

Environment::ValueModel Model;
Environment EnvJoined = Environment::join(Env1, Env2, Model);
auto *JoinedVal = cast<RecordValue>(EnvJoined.getValue(*ConstructExpr));
EXPECT_NE(JoinedVal, &Val1);
EXPECT_NE(JoinedVal, &Val2);
EXPECT_EQ(&JoinedVal->getLoc(), &Loc);
}

// Two different `RecordValue`s with different locations are joined into a
// third `RecordValue` with a location different from the other two.
{
Environment Env1(DAContext);
auto &Val1 = *cast<RecordValue>(Env1.createValue(Ty));
Env1.setValue(*ConstructExpr, Val1);

Environment Env2(DAContext);
auto &Val2 = *cast<RecordValue>(Env2.createValue(Ty));
Env2.setValue(*ConstructExpr, Val2);

Environment::ValueModel Model;
Environment EnvJoined = Environment::join(Env1, Env2, Model);
auto *JoinedVal = cast<RecordValue>(EnvJoined.getValue(*ConstructExpr));
EXPECT_NE(JoinedVal, &Val1);
EXPECT_NE(JoinedVal, &Val2);
EXPECT_NE(&JoinedVal->getLoc(), &Val1.getLoc());
EXPECT_NE(&JoinedVal->getLoc(), &Val2.getLoc());
}
}

TEST_F(EnvironmentTest, InitGlobalVarsFun) {
using namespace ast_matchers;

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