[llvm-branch-commits] [clang] [LifetimeSafety] Mark all DeclRefExpr as usages of the corresp. origin (PR #154316)
Utkarsh Saxena via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Wed Sep 3 07:03:56 PDT 2025
https://github.com/usx95 updated https://github.com/llvm/llvm-project/pull/154316
>From fffc8d6575370ff5f59379dca01b2c1396b52c50 Mon Sep 17 00:00:00 2001
From: Utkarsh Saxena <usx at google.com>
Date: Tue, 19 Aug 2025 12:00:53 +0000
Subject: [PATCH] Identify DeclRefExpr as a use of an origin
---
clang/lib/Analysis/LifetimeSafety.cpp | 91 +++++++++++++------
.../Sema/warn-lifetime-safety-dataflow.cpp | 26 ++++++
2 files changed, 90 insertions(+), 27 deletions(-)
diff --git a/clang/lib/Analysis/LifetimeSafety.cpp b/clang/lib/Analysis/LifetimeSafety.cpp
index 3c9ac9c48b2e5..947645852be36 100644
--- a/clang/lib/Analysis/LifetimeSafety.cpp
+++ b/clang/lib/Analysis/LifetimeSafety.cpp
@@ -118,6 +118,7 @@ class OriginManager {
return AllOrigins.back();
}
+ // TODO: Mark this method as const once we remove the call to getOrCreate.
OriginID get(const Expr &E) {
// Origin of DeclRefExpr is that of the declaration it refers to.
if (const auto *DRE = dyn_cast<DeclRefExpr>(&E))
@@ -314,22 +315,28 @@ class ReturnOfOriginFact : public Fact {
};
class UseFact : public Fact {
- OriginID UsedOrigin;
const Expr *UseExpr;
+ // True if this use is a write operation (e.g., left-hand side of assignment).
+ // Write operations are exempted from use-after-free checks.
+ bool IsWritten = false;
public:
static bool classof(const Fact *F) { return F->getKind() == Kind::Use; }
- UseFact(OriginID UsedOrigin, const Expr *UseExpr)
- : Fact(Kind::Use), UsedOrigin(UsedOrigin), UseExpr(UseExpr) {}
+ UseFact(const Expr *UseExpr) : Fact(Kind::Use), UseExpr(UseExpr) {}
- OriginID getUsedOrigin() const { return UsedOrigin; }
+ OriginID getUsedOrigin(const OriginManager &OM) const {
+ // TODO: Remove const cast and make OriginManager::get as const.
+ return const_cast<OriginManager &>(OM).get(*UseExpr);
+ }
const Expr *getUseExpr() const { return UseExpr; }
+ void markAsWritten() { IsWritten = true; }
+ bool isWritten() const { return IsWritten; }
void dump(llvm::raw_ostream &OS, const OriginManager &OM) const override {
OS << "Use (";
- OM.dump(getUsedOrigin(), OS);
- OS << ")\n";
+ OM.dump(getUsedOrigin(OM), OS);
+ OS << " " << (isWritten() ? "Write" : "Read") << ")\n";
}
};
@@ -436,6 +443,8 @@ class FactGenerator : public ConstStmtVisitor<FactGenerator> {
addAssignOriginFact(*VD, *InitExpr);
}
+ void VisitDeclRefExpr(const DeclRefExpr *DRE) { handleUse(DRE); }
+
void VisitCXXNullPtrLiteralExpr(const CXXNullPtrLiteralExpr *N) {
/// TODO: Handle nullptr expr as a special 'null' loan. Uninitialized
/// pointers can use the same type of loan.
@@ -469,10 +478,6 @@ class FactGenerator : public ConstStmtVisitor<FactGenerator> {
}
}
}
- } else if (UO->getOpcode() == UO_Deref) {
- // This is a pointer use, like '*p'.
- OriginID OID = FactMgr.getOriginMgr().get(*UO->getSubExpr());
- CurrentBlockFacts.push_back(FactMgr.createFact<UseFact>(OID, UO));
}
}
@@ -487,20 +492,13 @@ class FactGenerator : public ConstStmtVisitor<FactGenerator> {
}
void VisitBinaryOperator(const BinaryOperator *BO) {
- if (BO->isAssignmentOp()) {
- const Expr *LHSExpr = BO->getLHS();
- const Expr *RHSExpr = BO->getRHS();
-
- // We are interested in assignments like `ptr1 = ptr2` or `ptr = &var`
- // LHS must be a pointer/reference type that can be an origin.
- // RHS must also represent an origin (either another pointer/ref or an
- // address-of).
- if (const auto *DRE_LHS = dyn_cast<DeclRefExpr>(LHSExpr))
- if (const auto *VD_LHS =
- dyn_cast<ValueDecl>(DRE_LHS->getDecl()->getCanonicalDecl());
- VD_LHS && hasOrigin(VD_LHS->getType()))
- addAssignOriginFact(*VD_LHS, *RHSExpr);
- }
+ if (BO->isAssignmentOp())
+ handleAssignment(BO->getLHS(), BO->getRHS());
+ }
+
+ void VisitCXXOperatorCallExpr(const CXXOperatorCallExpr *OCE) {
+ if (OCE->isAssignmentOp() && OCE->getNumArgs() == 2)
+ handleAssignment(OCE->getArg(0), OCE->getArg(1));
}
void VisitCXXFunctionalCastExpr(const CXXFunctionalCastExpr *FCE) {
@@ -567,9 +565,47 @@ class FactGenerator : public ConstStmtVisitor<FactGenerator> {
return false;
}
+ void handleAssignment(const Expr *LHSExpr, const Expr *RHSExpr) {
+ // Find the underlying variable declaration for the left-hand side.
+ if (const auto *DRE_LHS =
+ dyn_cast<DeclRefExpr>(LHSExpr->IgnoreParenImpCasts())) {
+ markUseAsWrite(DRE_LHS);
+ if (const auto *VD_LHS = dyn_cast<ValueDecl>(DRE_LHS->getDecl()))
+ if (hasOrigin(LHSExpr->getType()))
+ // We are interested in assignments like `ptr1 = ptr2` or `ptr = &var`
+ // LHS must be a pointer/reference type that can be an origin.
+ // RHS must also represent an origin (either another pointer/ref or an
+ // address-of).
+ addAssignOriginFact(*VD_LHS, *RHSExpr);
+ }
+ }
+
+ // A DeclRefExpr is a use of the referenced decl. It is checked for
+ // use-after-free unless it is being written to (e.g. on the left-hand side
+ // of an assignment).
+ void handleUse(const DeclRefExpr *DRE) {
+ if (hasOrigin(DRE->getType())) {
+ UseFact *UF = FactMgr.createFact<UseFact>(DRE);
+ CurrentBlockFacts.push_back(UF);
+ assert(!UseFacts.contains(DRE));
+ UseFacts[DRE] = UF;
+ }
+ }
+
+ void markUseAsWrite(const DeclRefExpr *DRE) {
+ assert(UseFacts.contains(DRE));
+ UseFacts[DRE]->markAsWritten();
+ }
+
FactManager &FactMgr;
- AnalysisDeclContext &AC;
+ AnalysisDeclContext& AC;
llvm::SmallVector<Fact *> CurrentBlockFacts;
+ // To distinguish between reads and writes for use-after-free checks, this map
+ // stores the `UseFact` for each `DeclRefExpr`. We initially identify all
+ // `DeclRefExpr`s as "read" uses. When an assignment is processed, the use
+ // corresponding to the left-hand side is updated to be a "write", thereby
+ // exempting it from the check.
+ llvm::DenseMap<const DeclRefExpr *, UseFact *> UseFacts;
};
// ========================================================================= //
@@ -1032,8 +1068,9 @@ class LifetimeChecker {
/// graph. It determines if the loans held by the used origin have expired
/// at the point of use.
void checkUse(const UseFact *UF) {
-
- OriginID O = UF->getUsedOrigin();
+ if (UF->isWritten())
+ return;
+ OriginID O = UF->getUsedOrigin(FactMgr.getOriginMgr());
// Get the set of loans that the origin might hold at this program point.
LoanSet HeldLoans = LoanPropagation.getLoans(O, UF);
diff --git a/clang/test/Sema/warn-lifetime-safety-dataflow.cpp b/clang/test/Sema/warn-lifetime-safety-dataflow.cpp
index bc7e0127e5d4c..11437d024b693 100644
--- a/clang/test/Sema/warn-lifetime-safety-dataflow.cpp
+++ b/clang/test/Sema/warn-lifetime-safety-dataflow.cpp
@@ -312,3 +312,29 @@ void ternary_operator() {
// CHECK: AssignOrigin (Dest: [[O_P:[0-9]+]] (Decl: p), Src: {{[0-9]+}} (Expr: ConditionalOperator))
// CHECK: End of Block
}
+
+// CHECK-LABEL: Function: test_use_facts
+void usePointer(MyObj*);
+void test_use_facts() {
+ // CHECK: Block B{{[0-9]+}}:
+ MyObj x;
+ MyObj *p;
+ p = &x;
+ // CHECK: Use ([[O_P:[0-9]+]] (Decl: p) Write)
+ (void)*p;
+ // CHECK: Use ([[O_P]] (Decl: p) Read)
+ usePointer(p);
+ // CHECK: Use ([[O_P]] (Decl: p) Read)
+ p->id = 1;
+ // CHECK: Use ([[O_P]] (Decl: p) Read)
+
+
+ MyObj* q;
+ q = p;
+ // CHECK: Use ([[O_P]] (Decl: p) Read)
+ // CHECK: Use ([[O_Q:[0-9]+]] (Decl: q) Write)
+ usePointer(q);
+ // CHECK: Use ([[O_Q]] (Decl: q) Read)
+ q->id = 2;
+ // CHECK: Use ([[O_Q]] (Decl: q) Read)
+}
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