[AST][RecoveryExpr] Populate the dependence bits from CompoundStmt result expr to StmtExpr.

Summary:
We lost errorBit for StmtExpr if a recoveryExpr is the result
expr of a CompoundStmt, which will lead to crashes.

```
// `-StmtExpr
//   `-CompoundStmt
//     `-RecoveryExp
({ invalid(); });
```

Reviewers: sammccall

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D81154

clang/lib/AST/ComputeDependence.cpp

@@ -128,15 +128,19 @@ ExprDependence clang::computeDependence(BinaryConditionalOperator *E) {
 }
 
 ExprDependence clang::computeDependence(StmtExpr *E, unsigned TemplateDepth) {
-  // FIXME: why is unexpanded-pack not propagated?
+  auto D = toExprDependence(E->getType()->getDependence());
-  auto D = toExprDependence(E->getType()->getDependence()) &
+  // Propagate dependence of the result.
-           ~ExprDependence::UnexpandedPack;
+  if (const auto *CompoundExprResult =
+          dyn_cast_or_null<ValueStmt>(E->getSubStmt()->getStmtExprResult()))
+    if (const Expr *ResultExpr = CompoundExprResult->getExprStmt())
+      D |= ResultExpr->getDependence();
   // Note: we treat a statement-expression in a dependent context as always
   // being value- and instantiation-dependent. This matches the behavior of
   // lambda-expressions and GCC.
   if (TemplateDepth)
     D |= ExprDependence::ValueInstantiation;
-  return D;
+  // A param pack cannot be expanded over stmtexpr boundaries.
+  return D & ~ExprDependence::UnexpandedPack;
 }
 
 ExprDependence clang::computeDependence(ConvertVectorExpr *E) {

clang/test/SemaCXX/invalid-constructor-init.cpp

@@ -14,6 +14,12 @@ struct X2 {
   constexpr X2() {} // expected-error {{constexpr constructor never produces a constant expression}}
 };
 
+struct X3 {
+  int Y;
+  constexpr X3() // expected-error {{constexpr constructor never produces}}
+      : Y(({foo();})) {} // expected-error {{use of undeclared identifier 'foo'}}
+};
+
 struct CycleDelegate {
   int Y;
   CycleDelegate(int)