[clang] [LifetimeSafety] Implement multi-level origins (PR #168344)

[Gábor Horváth via cfe-commits]

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@@ -314,39 +474,34 @@ bool FactsGenerator::handleTestPoint(const CXXFunctionalCastExpr *FCE) {
   return false;
 }
 
-void FactsGenerator::handleAssignment(const Expr *LHSExpr,
-                                      const Expr *RHSExpr) {
-  if (!hasOrigin(LHSExpr))
-    return;
-  // 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())) {
-      // Kill the old loans of the destination origin and flow the new loans
-      // from the source origin.
-      killAndFlowOrigin(*VD_LHS, *RHSExpr);
-    }
-  }
-}
-
 // A DeclRefExpr will be treated as a use of the referenced decl. It will be
 // checked for use-after-free unless it is later marked as being written to
 // (e.g. on the left-hand side of an assignment).
 void FactsGenerator::handleUse(const DeclRefExpr *DRE) {
-  if (isPointerType(DRE->getType())) {
-    UseFact *UF = FactMgr.createFact<UseFact>(DRE, FactMgr.getOriginMgr());
-    CurrentBlockFacts.push_back(UF);
-    assert(!UseFacts.contains(DRE));
-    UseFacts[DRE] = UF;
+  OriginList *List = getOriginsList(*DRE);
+  if (!List)
+    return;
+  // Remove the outer layer of origin which borrows from the decl directly. This
+  // is a use of the underlying decl.
+  List = getRValueOrigins(DRE, List);
+  // Skip if there is no inner origin (e.g., when it is not a pointer type).
+  if (!List)
+    return;
+  llvm::SmallVector<OriginID> UsedOrigins;
+  OriginList *L = List;
+  while (L) {
+    UsedOrigins.push_back(L->getOuterOriginID());
+    L = L->peelOuterOrigin();
   }
+  UseFact *UF = FactMgr.createFact<UseFact>(DRE, std::move(UsedOrigins));
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Xazax-hun wrote:

I wonder if the code would be simpler if we always had the same format everywhere for origin lists. E.g., if `UseFact` took an `OriginList` instead of a `SmallVector`. Might make it easier to switch to a tree in the future if we need it. 

https://github.com/llvm/llvm-project/pull/168344