[llvm-branch-commits] [clang] [LifetimeSafety] Mark all DeclRefExpr as usages of the corresp. origin (PR #154316)

[Gábor Horváth via llvm-branch-commits]

================
@@ -556,8 +554,47 @@ 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())) {
+      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;
   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;
----------------
Xazax-hun wrote:

What is the plan for writes we have no DREs for? Like:
```
  (cond ? a : b) = ptr;
```

https://github.com/llvm/llvm-project/pull/154316