[analyzer] Model trivial copy/move assignment operators with a bind as well.

r175234 allowed the analyzer to model trivial copy/move constructors as
an aggregate bind. This commit extends that to trivial assignment
operators as well. Like the last commit, one of the motivating factors here
is not warning when the right-hand object is partially-initialized, which
can have legitimate uses.

<rdar://problem/13405162>

llvm-svn: 177220

1 files changed, 28 insertions, 9 deletions

diff --git a/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp b/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
index 32b522cbd5b..d1a591c7fe0 100644
--- a/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
+++ b/clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp
@@ -48,13 +48,25 @@ void ExprEngine::CreateCXXTemporaryObject(const MaterializeTemporaryExpr *ME,
   Bldr.generateNode(ME, Pred, state);
 }
 
+// FIXME: This is the sort of code that should eventually live in a Core
+// checker rather than as a special case in ExprEngine.
 void ExprEngine::performTrivialCopy(NodeBuilder &Bldr, ExplodedNode *Pred,
-                                    const CXXConstructorCall &Call) {
-  const CXXConstructExpr *CtorExpr = Call.getOriginExpr();
-  assert(CtorExpr->getConstructor()->isCopyOrMoveConstructor());
-  assert(CtorExpr->getConstructor()->isTrivial());
+                                    const CallEvent &Call) {
+  SVal ThisVal;
+  bool AlwaysReturnsLValue;
+  if (const CXXConstructorCall *Ctor = dyn_cast<CXXConstructorCall>(&Call)) {
+    assert(Ctor->getDecl()->isTrivial());
+    assert(Ctor->getDecl()->isCopyOrMoveConstructor());
+    ThisVal = Ctor->getCXXThisVal();
+    AlwaysReturnsLValue = false;
+  } else {
+    assert(cast<CXXMethodDecl>(Call.getDecl())->isTrivial());
+    assert(cast<CXXMethodDecl>(Call.getDecl())->getOverloadedOperator() ==
+           OO_Equal);
+    ThisVal = cast<CXXInstanceCall>(Call).getCXXThisVal();
+    AlwaysReturnsLValue = true;
+  }
 
-  SVal ThisVal = Call.getCXXThisVal();
   const LocationContext *LCtx = Pred->getLocationContext();
 
   ExplodedNodeSet Dst;
@@ -62,17 +74,24 @@ void ExprEngine::performTrivialCopy(NodeBuilder &Bldr, ExplodedNode *Pred,
 
   SVal V = Call.getArgSVal(0);
 
-  // Make sure the value being copied is not unknown.
+  // If the value being copied is not unknown, load from its location to get
+  // an aggregate rvalue.
   if (Optional<Loc> L = V.getAs<Loc>())
     V = Pred->getState()->getSVal(*L);
+  else
+    assert(V.isUnknown());
 
-  evalBind(Dst, CtorExpr, Pred, ThisVal, V, true);
+  const Expr *CallExpr = Call.getOriginExpr();
+  evalBind(Dst, CallExpr, Pred, ThisVal, V, true);
 
-  PostStmt PS(CtorExpr, LCtx);
+  PostStmt PS(CallExpr, LCtx);
   for (ExplodedNodeSet::iterator I = Dst.begin(), E = Dst.end();
        I != E; ++I) {
     ProgramStateRef State = (*I)->getState();
-    State = bindReturnValue(Call, LCtx, State);
+    if (AlwaysReturnsLValue)
+      State = State->BindExpr(CallExpr, LCtx, ThisVal);
+    else
+      State = bindReturnValue(Call, LCtx, State);
     Bldr.generateNode(PS, State, *I);
   }
 }