PR43762: when implicitly changing the active union member for an

assignment during constant evaluation, only start the lifetime of
trivially-default-constructible union members.

1 files changed, 10 insertions, 3 deletions

diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 42c746e6028..7ed08218567 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -5333,9 +5333,16 @@ static bool HandleUnionActiveMemberChange(EvalInfo &Info, const Expr *LHSExpr,
       if (!FD || FD->getType()->isReferenceType())
         break;
 
-      //    ... and also contains A.B if B names a union member
-      if (FD->getParent()->isUnion())
-        UnionPathLengths.push_back({PathLength - 1, FD});
+      //    ... and also contains A.B if B names a union member ...
+      if (FD->getParent()->isUnion()) {
+        //    ... of a non-class, non-array type, or of a class type with a
+        //    trivial default constructor that is not deleted, or an array of
+        //    such types.
+        auto *RD =
+            FD->getType()->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
+        if (!RD || RD->hasTrivialDefaultConstructor())
+          UnionPathLengths.push_back({PathLength - 1, FD});
+      }
 
       E = ME->getBase();
       --PathLength;