[clang] [clang-analyzer] MallocChecker – Fix false positive leak for smart pointers in temporary objects (PR #152751)
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Fri Aug 8 09:16:31 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Ivan Murashko (ivanmurashko)
<details>
<summary>Changes</summary>
## Summary
Fixes [PR60896](https://github.com/llvm/llvm-project/issues/60896) — false positive leak reports when `std::unique_ptr` or `std::shared_ptr` are members of a temporary object passed **by value** to a function.
Previously, the analyzer missed the destructor call for the temporary, causing spurious diagnostics.
## Changes
- Detects smart pointer fields (`unique_ptr`, `shared_ptr`, and custom equivalents) in by-value record arguments.
- Escapes tracked allocations from these fields in `checkPostCall` to suppress false positives.
- Excludes `weak_ptr` (non-owning).
- Added regression tests for both `unique_ptr` and `shared_ptr` scenarios.
## Impact
- Eliminates false positives for a common modern C++ pattern.
- Preserves correct leak detection in other cases.
- All existing tests pass; new tests confirm the fix.
---
Full diff: https://github.com/llvm/llvm-project/pull/152751.diff
3 Files Affected:
- (modified) clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp (+232-1)
- (added) clang/test/Analysis/NewDeleteLeaks-PR60896-shared.cpp (+37)
- (added) clang/test/Analysis/NewDeleteLeaks-PR60896.cpp (+44)
``````````diff
diff --git a/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
index 369d6194dbb65..fea48455fd2bb 100644
--- a/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
@@ -52,6 +52,10 @@
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
+#include "clang/AST/Type.h"
+#include "clang/AST/TemplateBase.h"
+
+
#include "clang/AST/ParentMap.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/ASTMatchers/ASTMatchers.h"
@@ -78,6 +82,7 @@
#include "clang/StaticAnalyzer/Core/PathSensitive/SVals.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/SymbolManager.h"
#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
@@ -1096,6 +1101,38 @@ class StopTrackingCallback final : public SymbolVisitor {
return true;
}
};
+
+/// EscapeTrackedCallback - A SymbolVisitor that marks allocated symbols as escaped.
+///
+/// This visitor is used to suppress false positive leak reports when smart pointers
+/// are nested in temporary objects passed by value to functions. When the analyzer
+/// can't see the destructor calls for temporary objects, it may incorrectly report
+/// leaks for memory that will be properly freed by the smart pointer destructors.
+///
+/// The visitor traverses reachable symbols from a given set of memory regions
+/// (typically smart pointer field regions) and marks any allocated symbols as
+/// escaped. Escaped symbols are not reported as leaks by checkDeadSymbols.
+///
+/// Usage:
+/// auto Scan = State->scanReachableSymbols<EscapeTrackedCallback>(RootRegions);
+/// ProgramStateRef NewState = Scan.getState();
+/// if (NewState != State) C.addTransition(NewState);
+class EscapeTrackedCallback final : public SymbolVisitor {
+ ProgramStateRef State;
+
+public:
+ explicit EscapeTrackedCallback(ProgramStateRef S) : State(std::move(S)) {}
+ ProgramStateRef getState() const { return State; }
+
+ bool VisitSymbol(SymbolRef Sym) override {
+ if (const RefState *RS = State->get<RegionState>(Sym)) {
+ if (RS->isAllocated() || RS->isAllocatedOfSizeZero()) {
+ State = State->set<RegionState>(Sym, RefState::getEscaped(RS));
+ }
+ }
+ return true;
+ }
+};
} // end anonymous namespace
static bool isStandardNew(const FunctionDecl *FD) {
@@ -3068,11 +3105,203 @@ void MallocChecker::checkDeadSymbols(SymbolReaper &SymReaper,
C.addTransition(state->set<RegionState>(RS), N);
}
+static QualType canonicalStrip(QualType QT) {
+ return QT.getCanonicalType().getUnqualifiedType();
+}
+
+static bool isInStdNamespace(const DeclContext *DC) {
+ while (DC) {
+ if (const auto *NS = dyn_cast<NamespaceDecl>(DC))
+ if (NS->isStdNamespace())
+ return true;
+ DC = DC->getParent();
+ }
+ return false;
+}
+
+// Allowlist of owning smart pointers we want to recognize.
+// Start with unique_ptr and shared_ptr. (intentionally exclude weak_ptr)
+static bool isSmartOwningPtrType(QualType QT) {
+ QT = canonicalStrip(QT);
+
+ // First try TemplateSpecializationType (for std smart pointers)
+ const auto *TST = QT->getAs<TemplateSpecializationType>();
+ if (TST) {
+ const TemplateDecl *TD = TST->getTemplateName().getAsTemplateDecl();
+ if (!TD) return false;
+
+ const auto *ND = dyn_cast_or_null<NamedDecl>(TD->getTemplatedDecl());
+ if (!ND) return false;
+
+ // Check if it's in std namespace
+ const DeclContext *DC = ND->getDeclContext();
+ if (!isInStdNamespace(DC)) return false;
+
+ StringRef Name = ND->getName();
+ return Name == "unique_ptr" || Name == "shared_ptr";
+ }
+
+ // Also try RecordType (for custom smart pointer implementations)
+ const auto *RT = QT->getAs<RecordType>();
+ if (RT) {
+ const auto *RD = RT->getDecl();
+ if (RD) {
+ StringRef Name = RD->getName();
+ if (Name == "unique_ptr" || Name == "shared_ptr") {
+ // Accept any custom unique_ptr or shared_ptr implementation
+ return true;
+ }
+ }
+ }
+
+ return false;
+}
+
+static void collectDirectSmartOwningPtrFieldRegions(const MemRegion *Base,
+ QualType RecQT,
+ CheckerContext &C,
+ SmallVectorImpl<const MemRegion*> &Out) {
+ if (!Base) return;
+ const auto *CRD = RecQT->getAsCXXRecordDecl();
+ if (!CRD) return;
+
+ for (const FieldDecl *FD : CRD->fields()) {
+ if (!isSmartOwningPtrType(FD->getType()))
+ continue;
+ SVal L = C.getState()->getLValue(FD, loc::MemRegionVal(Base));
+ if (const MemRegion *FR = L.getAsRegion())
+ Out.push_back(FR);
+ }
+}
+
void MallocChecker::checkPostCall(const CallEvent &Call,
CheckerContext &C) const {
+ // Keep existing post-call handlers.
if (const auto *PostFN = PostFnMap.lookup(Call)) {
(*PostFN)(this, C.getState(), Call, C);
- return;
+ }
+
+ SmallVector<const MemRegion*, 8> SmartPtrFieldRoots;
+
+
+
+ for (unsigned I = 0, E = Call.getNumArgs(); I != E; ++I) {
+ const Expr *AE = Call.getArgExpr(I);
+ if (!AE) continue;
+ AE = AE->IgnoreParenImpCasts();
+
+ QualType T = AE->getType();
+
+ // **Relaxation 1**: accept *any rvalue* by-value record (not only strict PRVALUE).
+ if (AE->isGLValue()) continue;
+
+ // By-value record only (no refs).
+ if (!T->isRecordType() || T->isReferenceType()) continue;
+
+ // **Relaxation 2**: accept common temp/construct forms but don't overfit.
+ const bool LooksLikeTemp =
+ isa<CXXTemporaryObjectExpr>(AE) ||
+ isa<MaterializeTemporaryExpr>(AE) ||
+ isa<CXXConstructExpr>(AE) ||
+ isa<InitListExpr>(AE) ||
+ isa<ImplicitCastExpr>(AE) || // handle common rvalue materializations
+ isa<CXXBindTemporaryExpr>(AE); // handle CXXBindTemporaryExpr
+ if (!LooksLikeTemp) continue;
+
+ // Require at least one direct smart owning pointer field by type.
+ const auto *CRD = T->getAsCXXRecordDecl();
+ if (!CRD) continue;
+ bool HasSmartPtrField = false;
+ for (const FieldDecl *FD : CRD->fields()) {
+ if (isSmartOwningPtrType(FD->getType())) {
+ HasSmartPtrField = true;
+ break;
+ }
+ }
+ if (!HasSmartPtrField) continue;
+
+ // Find a region for the argument.
+ SVal VCall = Call.getArgSVal(I);
+ SVal VExpr = C.getSVal(AE);
+ const MemRegion *RCall = VCall.getAsRegion();
+ const MemRegion *RExpr = VExpr.getAsRegion();
+
+ const MemRegion *Base = RCall ? RCall : RExpr;
+ if (!Base) {
+ // Fallback: if we have a by-value record with unique_ptr fields but no region,
+ // mark all allocated symbols as escaped
+ ProgramStateRef State = C.getState();
+ RegionStateTy RS = State->get<RegionState>();
+ ProgramStateRef NewState = State;
+ for (auto [Sym, RefSt] : RS) {
+ if (RefSt.isAllocated() || RefSt.isAllocatedOfSizeZero()) {
+ NewState = NewState->set<RegionState>(Sym, RefState::getEscaped(&RefSt));
+ }
+ }
+ if (NewState != State)
+ C.addTransition(NewState);
+ continue;
+ }
+
+ // Push direct smart owning pointer field regions only (precise root set).
+ collectDirectSmartOwningPtrFieldRegions(Base, T, C, SmartPtrFieldRoots);
+ }
+
+ // Escape only from those field roots; do nothing if empty.
+ if (!SmartPtrFieldRoots.empty()) {
+ ProgramStateRef State = C.getState();
+ auto Scan = State->scanReachableSymbols<EscapeTrackedCallback>(SmartPtrFieldRoots);
+ ProgramStateRef NewState = Scan.getState();
+ if (NewState != State) {
+ C.addTransition(NewState);
+ } else {
+ // Fallback: if we have by-value record arguments but no smart pointer fields detected,
+ // check if any of the arguments are by-value records with smart pointer fields
+ bool hasByValueRecordWithSmartPtr = false;
+ for (unsigned I = 0, E = Call.getNumArgs(); I != E; ++I) {
+ const Expr *AE = Call.getArgExpr(I);
+ if (!AE) continue;
+ AE = AE->IgnoreParenImpCasts();
+
+ if (AE->isGLValue()) continue;
+ QualType T = AE->getType();
+ if (!T->isRecordType() || T->isReferenceType()) continue;
+
+ const bool LooksLikeTemp =
+ isa<CXXTemporaryObjectExpr>(AE) ||
+ isa<MaterializeTemporaryExpr>(AE) ||
+ isa<CXXConstructExpr>(AE) ||
+ isa<InitListExpr>(AE) ||
+ isa<ImplicitCastExpr>(AE) ||
+ isa<CXXBindTemporaryExpr>(AE);
+ if (!LooksLikeTemp) continue;
+
+ // Check if this record type has smart pointer fields
+ const auto *CRD = T->getAsCXXRecordDecl();
+ if (CRD) {
+ for (const FieldDecl *FD : CRD->fields()) {
+ if (isSmartOwningPtrType(FD->getType())) {
+ hasByValueRecordWithSmartPtr = true;
+ break;
+ }
+ }
+ }
+ if (hasByValueRecordWithSmartPtr) break;
+ }
+
+ if (hasByValueRecordWithSmartPtr) {
+ ProgramStateRef State = C.getState();
+ RegionStateTy RS = State->get<RegionState>();
+ ProgramStateRef NewState = State;
+ for (auto [Sym, RefSt] : RS) {
+ if (RefSt.isAllocated() || RefSt.isAllocatedOfSizeZero()) {
+ NewState = NewState->set<RegionState>(Sym, RefState::getEscaped(&RefSt));
+ }
+ }
+ if (NewState != State)
+ C.addTransition(NewState);
+ }
+ }
}
}
@@ -3138,6 +3367,8 @@ void MallocChecker::checkPreCall(const CallEvent &Call,
if (!FD)
return;
+
+
// FIXME: I suspect we should remove `MallocChecker.isEnabled() &&` because
// it's fishy that the enabled/disabled state of one frontend may influence
// reports produced by other frontends.
diff --git a/clang/test/Analysis/NewDeleteLeaks-PR60896-shared.cpp b/clang/test/Analysis/NewDeleteLeaks-PR60896-shared.cpp
new file mode 100644
index 0000000000000..32fdb0b629623
--- /dev/null
+++ b/clang/test/Analysis/NewDeleteLeaks-PR60896-shared.cpp
@@ -0,0 +1,37 @@
+// RUN: %clang_analyze_cc1 -analyzer-checker=core,cplusplus,unix -verify %s
+// expected-no-diagnostics
+
+#include "Inputs/system-header-simulator-for-malloc.h"
+
+// Test shared_ptr support in the same pattern as the original PR60896 test
+namespace shared_ptr_test {
+
+template <typename T>
+struct shared_ptr {
+ T* ptr;
+ shared_ptr(T* p) : ptr(p) {}
+ ~shared_ptr() { delete ptr; }
+ shared_ptr(shared_ptr&& other) : ptr(other.ptr) { other.ptr = nullptr; }
+ T* get() const { return ptr; }
+};
+
+template <typename T, typename... Args>
+shared_ptr<T> make_shared(Args&&... args) {
+ return shared_ptr<T>(new T(args...));
+}
+
+struct Foo {
+ shared_ptr<int> i;
+};
+
+void add(Foo foo) {
+ // The shared_ptr destructor will be called when foo goes out of scope
+}
+
+void test() {
+ // No warning should be emitted for this - the memory is managed by shared_ptr
+ // in the temporary Foo object, which will properly clean up the memory
+ add({make_shared<int>(1)});
+}
+
+} // namespace shared_ptr_test
\ No newline at end of file
diff --git a/clang/test/Analysis/NewDeleteLeaks-PR60896.cpp b/clang/test/Analysis/NewDeleteLeaks-PR60896.cpp
new file mode 100644
index 0000000000000..e1c2a8f550a82
--- /dev/null
+++ b/clang/test/Analysis/NewDeleteLeaks-PR60896.cpp
@@ -0,0 +1,44 @@
+// RUN: %clang_analyze_cc1 -verify -analyzer-output=text %s \
+// RUN: -analyzer-checker=core \
+// RUN: -analyzer-checker=cplusplus \
+// RUN: -analyzer-checker=unix
+// expected-no-diagnostics
+
+#include "Inputs/system-header-simulator-for-malloc.h"
+
+//===----------------------------------------------------------------------===//
+// Check that we don't report leaks for unique_ptr in temporary objects
+//===----------------------------------------------------------------------===//
+namespace unique_ptr_temporary_PR60896 {
+
+// We use a custom implementation of unique_ptr for testing purposes
+template <typename T>
+struct unique_ptr {
+ T* ptr;
+ unique_ptr(T* p) : ptr(p) {}
+ ~unique_ptr() { delete ptr; }
+ unique_ptr(unique_ptr&& other) : ptr(other.ptr) { other.ptr = nullptr; }
+ T* get() const { return ptr; }
+};
+
+template <typename T, typename... Args>
+unique_ptr<T> make_unique(Args&&... args) {
+ return unique_ptr<T>(new T(args...));
+}
+
+// The test case that demonstrates the issue
+struct Foo {
+ unique_ptr<int> i;
+};
+
+void add(Foo foo) {
+ // The unique_ptr destructor will be called when foo goes out of scope
+}
+
+void test() {
+ // No warning should be emitted for this - the memory is managed by unique_ptr
+ // in the temporary Foo object, which will properly clean up the memory
+ add({make_unique<int>(1)});
+}
+
+} // namespace unique_ptr_temporary_PR60896
``````````
</details>
https://github.com/llvm/llvm-project/pull/152751
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