https://github.com/martinboehme updated
https://github.com/llvm/llvm-project/pull/90438
>From 2cf2947efb81c0aaf5953dd2c263370c724a01fb Mon Sep 17 00:00:00 2001
From: Martin Braenne <mboe...@google.com>
Date: Tue, 30 Apr 2024 12:06:42 +0000
Subject: [PATCH] [clang][dataflow] Don't propagate result objects in
unevaluated contexts.
Trying to do so can cause crashes -- see newly added test and the comments in
the fix.
We're starting to see a repeating pattern here: We're getting crashes because
`ResultObjectVisitor` and `getReferencedDecls()` don't agree on which parts of
the AST to visit and, hence, which fields should be modeled.
I think we should ensure consistency between these two parts of the code by
using a `RecursiveASTVisitor` in `getReferencedDecls()`[^1]; the
`Traverse...()` functions that control which parts of the AST we visit would go
in a common base class that would be used for both `ResultObjectVisitor` and
`getReferencedDecls()`.
I'd like to focus this PR, however, on a targeted fix for the current crash and
postpone the refactoring to a later PR (which will be easier to revert if there
are unintended side-effects).
[^1]: As an added bonus, this would make the code better structured and more
efficient than the current sequence of `if (dyn_cast<T>(...))` statements).
---
.../FlowSensitive/DataflowEnvironment.cpp | 11 ++++
.../Analysis/FlowSensitive/TransferTest.cpp | 52 +++++++++++++++++++
2 files changed, 63 insertions(+)
diff --git a/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
b/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
index d79e734402892a..cb6c8b2ef1072b 100644
--- a/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
+++ b/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
@@ -350,6 +350,17 @@ class ResultObjectVisitor : public
RecursiveASTVisitor<ResultObjectVisitor> {
return RecursiveASTVisitor<ResultObjectVisitor>::TraverseDecl(D);
}
+ // Don't traverse expressions in unevaluated contexts, as we don't model
+ // fields that are only used in these.
+ // Note: The operand of the `noexcept` operator is an unevaluated operand,
but
+ // nevertheless it appears in the Clang CFG, so we don't exclude it here.
+ bool TraverseDecltypeTypeLoc(DecltypeTypeLoc) { return true; }
+ bool TraverseTypeOfExprTypeLoc(TypeOfExprTypeLoc) { return true; }
+ bool TraverseCXXTypeidExpr(CXXTypeidExpr *) { return true; }
+ bool TraverseUnaryExprOrTypeTraitExpr(UnaryExprOrTypeTraitExpr *) {
+ return true;
+ }
+
bool TraverseBindingDecl(BindingDecl *BD) {
// `RecursiveASTVisitor` doesn't traverse holding variables for
// `BindingDecl`s by itself, so we need to tell it to.
diff --git a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
index 301bec32c0cf1d..95d5f569c0c824 100644
--- a/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
+++ b/clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
@@ -3331,6 +3331,58 @@ TEST(TransferTest,
ResultObjectLocationDontVisitNestedRecordDecl) {
ASTContext &ASTCtx) {});
}
+TEST(TransferTest, ResultObjectLocationDontVisitUnevaluatedContexts) {
+ // This is a crash repro.
+ // We used to crash because when propagating result objects, we would visit
+ // unevaluated contexts, but we don't model fields used only in these.
+
+ auto testFunction = [](llvm::StringRef Code, llvm::StringRef TargetFun) {
+ runDataflow(
+ Code,
+ [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+ ASTContext &ASTCtx) {},
+ LangStandard::lang_gnucxx17,
+ /* ApplyBuiltinTransfer= */ true, TargetFun);
+ };
+
+ std::string Code = R"cc(
+ // Definitions needed for `typeid`.
+ namespace std {
+ class type_info {};
+ class bad_typeid {};
+ } // namespace std
+
+ struct S1 {};
+ struct S2 { S1 s1; };
+
+ // We test each type of unevaluated context from a different target
+ // function. Some types of unevaluated contexts may actually cause the
+ // field `s1` to be modeled, and we don't want this to "pollute" the tests
+ // for the other unevaluated contexts.
+ void decltypeTarget() {
+ decltype(S2{}) Dummy;
+ }
+ void typeofTarget() {
+ typeof(S2{}) Dummy;
+ }
+ void typeidTarget() {
+ typeid(S2{});
+ }
+ void sizeofTarget() {
+ sizeof(S2{});
+ }
+ void noexceptTarget() {
+ noexcept(S2{});
+ }
+ )cc";
+
+ testFunction(Code, "decltypeTarget");
+ testFunction(Code, "typeofTarget");
+ testFunction(Code, "typeidTarget");
+ testFunction(Code, "sizeofTarget");
+ testFunction(Code, "noexceptTarget");
+}
+
TEST(TransferTest, StaticCast) {
std::string Code = R"(
void target(int Foo) {
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