From ca1034341cfec226c09ff0e473c6ecbcc2a1194c Mon Sep 17 00:00:00 2001
From: martinboehme <mboehme@google.com>
Date: Mon, 18 Dec 2023 09:10:03 +0100
Subject: [clang][dataflow] Fix an issue with
 `Environment::getResultObjectLocation()`. (#75483)

So far, if there was a chain of record type prvalues,
`getResultObjectLocation()` would assign a different result object
location to
each one. This makes no sense, of course, as all of these prvalues end
up
initializing the same result object.

This patch fixes this by propagating storage locations up through the
entire
chain of prvalues.

The new implementation also has the desirable effect of making it
possible to
make `getResultObjectLocation()` const, which seems appropriate given
that,
logically, it is just an accessor.
---
 .../Analysis/FlowSensitive/DataflowEnvironment.cpp | 79 ++++++++++++++++------
 1 file changed, 58 insertions(+), 21 deletions(-)

(limited to 'clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp')

diff --git a/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp b/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
index b98037b..93919cd 100644
--- a/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
+++ b/clang/lib/Analysis/FlowSensitive/DataflowEnvironment.cpp
@@ -726,27 +726,70 @@ void Environment::setStorageLocation(const Expr &E, StorageLocation &Loc) {
   // so allow these as an exception.
   assert(E.isGLValue() ||
          E.getType()->isSpecificBuiltinType(BuiltinType::BuiltinFn));
-  setStorageLocationInternal(E, Loc);
+  const Expr &CanonE = ignoreCFGOmittedNodes(E);
+  assert(!ExprToLoc.contains(&CanonE));
+  ExprToLoc[&CanonE] = &Loc;
 }
 
 StorageLocation *Environment::getStorageLocation(const Expr &E) const {
   // See comment in `setStorageLocation()`.
   assert(E.isGLValue() ||
          E.getType()->isSpecificBuiltinType(BuiltinType::BuiltinFn));
-  return getStorageLocationInternal(E);
+  auto It = ExprToLoc.find(&ignoreCFGOmittedNodes(E));
+  return It == ExprToLoc.end() ? nullptr : &*It->second;
+}
+
+// Returns whether a prvalue of record type is the one that originally
+// constructs the object (i.e. it doesn't propagate it from one of its
+// children).
+static bool isOriginalRecordConstructor(const Expr &RecordPRValue) {
+  if (auto *Init = dyn_cast<InitListExpr>(&RecordPRValue))
+    return !Init->isSemanticForm() || !Init->isTransparent();
+  return isa<CXXConstructExpr>(RecordPRValue) || isa<CallExpr>(RecordPRValue) ||
+         isa<LambdaExpr>(RecordPRValue) ||
+         // The framework currently does not propagate the objects created in
+         // the two branches of a `ConditionalOperator` because there is no way
+         // to reconcile their storage locations, which are different. We
+         // therefore claim that the `ConditionalOperator` is the expression
+         // that originally constructs the object.
+         // Ultimately, this will be fixed by propagating locations down from
+         // the result object, rather than up from the original constructor as
+         // we do now (see also the FIXME in the documentation for
+         // `getResultObjectLocation()`).
+         isa<ConditionalOperator>(RecordPRValue);
 }
 
 RecordStorageLocation &
-Environment::getResultObjectLocation(const Expr &RecordPRValue) {
+Environment::getResultObjectLocation(const Expr &RecordPRValue) const {
   assert(RecordPRValue.getType()->isRecordType());
   assert(RecordPRValue.isPRValue());
 
-  if (StorageLocation *ExistingLoc = getStorageLocationInternal(RecordPRValue))
-    return *cast<RecordStorageLocation>(ExistingLoc);
-  auto &Loc = cast<RecordStorageLocation>(
-      DACtx->getStableStorageLocation(RecordPRValue));
-  setStorageLocationInternal(RecordPRValue, Loc);
-  return Loc;
+  // Returns a storage location that we can use if assertions fail.
+  auto FallbackForAssertFailure =
+      [this, &RecordPRValue]() -> RecordStorageLocation & {
+    return cast<RecordStorageLocation>(
+        DACtx->getStableStorageLocation(RecordPRValue));
+  };
+
+  if (isOriginalRecordConstructor(RecordPRValue)) {
+    auto *Val = cast_or_null<RecordValue>(getValue(RecordPRValue));
+    // The builtin transfer function should have created a `RecordValue` for all
+    // original record constructors.
+    assert(Val);
+    if (!Val)
+      return FallbackForAssertFailure();
+    return Val->getLoc();
+  }
+
+  // Expression nodes that propagate a record prvalue should have exactly one
+  // child.
+  llvm::SmallVector<const Stmt *> children(RecordPRValue.child_begin(),
+                                           RecordPRValue.child_end());
+  assert(children.size() == 1);
+  if (children.empty())
+    return FallbackForAssertFailure();
+
+  return getResultObjectLocation(*cast<Expr>(children[0]));
 }
 
 PointerValue &Environment::getOrCreateNullPointerValue(QualType PointeeType) {
@@ -760,6 +803,11 @@ void Environment::setValue(const StorageLocation &Loc, Value &Val) {
 }
 
 void Environment::setValue(const Expr &E, Value &Val) {
+  if (auto *RecordVal = dyn_cast<RecordValue>(&Val)) {
+    assert(isOriginalRecordConstructor(E) ||
+           &RecordVal->getLoc() == &getResultObjectLocation(E));
+  }
+
   assert(E.isPRValue());
   ExprToVal[&E] = &Val;
 }
@@ -799,18 +847,6 @@ Value *Environment::createValue(QualType Type) {
   return Val;
 }
 
-void Environment::setStorageLocationInternal(const Expr &E,
-                                             StorageLocation &Loc) {
-  const Expr &CanonE = ignoreCFGOmittedNodes(E);
-  assert(!ExprToLoc.contains(&CanonE));
-  ExprToLoc[&CanonE] = &Loc;
-}
-
-StorageLocation *Environment::getStorageLocationInternal(const Expr &E) const {
-  auto It = ExprToLoc.find(&ignoreCFGOmittedNodes(E));
-  return It == ExprToLoc.end() ? nullptr : &*It->second;
-}
-
 Value *Environment::createValueUnlessSelfReferential(
     QualType Type, llvm::DenseSet<QualType> &Visited, int Depth,
     int &CreatedValuesCount) {
@@ -1044,6 +1080,7 @@ RecordValue &refreshRecordValue(const Expr &Expr, Environment &Env) {
     if (auto *ExistingVal = cast_or_null<RecordValue>(Env.getValue(Expr))) {
       auto &NewVal = Env.create<RecordValue>(ExistingVal->getLoc());
       Env.setValue(Expr, NewVal);
+      Env.setValue(NewVal.getLoc(), NewVal);
       return NewVal;
     }
 
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