https://github.com/usx95 created
https://github.com/llvm/llvm-project/pull/154316
None
>From 9855655fbbdc93951cf8e7560f48c28bd9393208 Mon Sep 17 00:00:00 2001
From: Utkarsh Saxena <u...@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 | 69 +++++++++++++++++++--------
1 file changed, 50 insertions(+), 19 deletions(-)
diff --git a/clang/lib/Analysis/LifetimeSafety.cpp
b/clang/lib/Analysis/LifetimeSafety.cpp
index fb2ae690cdd60..5fa769b0977e4 100644
--- a/clang/lib/Analysis/LifetimeSafety.cpp
+++ b/clang/lib/Analysis/LifetimeSafety.cpp
@@ -299,6 +299,7 @@ class ReturnOfOriginFact : public Fact {
class UseFact : public Fact {
OriginID UsedOrigin;
const Expr *UseExpr;
+ bool IsWritten = false;
public:
static bool classof(const Fact *F) { return F->getKind() == Kind::Use; }
@@ -308,6 +309,8 @@ class UseFact : public Fact {
OriginID getUsedOrigin() const { return UsedOrigin; }
const Expr *getUseExpr() const { return UseExpr; }
+ void markAsWritten() { IsWritten = true; }
+ bool isWritten() const { return IsWritten; }
void dump(llvm::raw_ostream &OS) const override {
OS << "Use (OriginID: " << UsedOrigin << ")\n";
@@ -408,6 +411,8 @@ class FactGeneratorVisitor : public
ConstStmtVisitor<FactGeneratorVisitor> {
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.
@@ -441,10 +446,6 @@ class FactGeneratorVisitor : public
ConstStmtVisitor<FactGeneratorVisitor> {
}
}
}
- } 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));
}
}
@@ -459,20 +460,13 @@ class FactGeneratorVisitor : public
ConstStmtVisitor<FactGeneratorVisitor> {
}
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) {
@@ -539,9 +533,45 @@ class FactGeneratorVisitor : public
ConstStmtVisitor<FactGeneratorVisitor> {
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(VD_LHS->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) {
+ const auto *VD = dyn_cast<ValueDecl>(DRE->getDecl());
+ if (VD && hasOrigin(VD->getType())) {
+ OriginID OID = FactMgr.getOriginMgr().get(*VD);
+ UseFact *UF = FactMgr.createFact<UseFact>(OID, 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;
const CFGBlock *CurrentBlock = nullptr;
llvm::SmallVector<Fact *> CurrentBlockFacts;
+ // Doc: Why do we need this ?
+ llvm::DenseMap<const DeclRefExpr *, UseFact *> UseFacts;
};
class FactGenerator : public RecursiveASTVisitor<FactGenerator> {
@@ -1056,7 +1086,8 @@ 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) {
-
+ if (UF->isWritten())
+ return;
OriginID O = UF->getUsedOrigin();
// Get the set of loans that the origin might hold at this program point.
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