fix aliasing issue in node_construct()

invisible so far, but the next patch uncovers it.

this could be possibly optimized for more compilers.
however, i found no way to ask msvc whether it is doing an
optimized build.

Reviewed-by: thiago

1 files changed, 8 insertions, 0 deletions

diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index dc8c849e8b..e3b8e1b545 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -377,7 +377,15 @@ Q_INLINE_TEMPLATE void QList<T>::node_construct(Node *n, const T &t)
 {
     if (QTypeInfo<T>::isLarge || QTypeInfo<T>::isStatic) n->v = new T(t);
     else if (QTypeInfo<T>::isComplex) new (n) T(t);
+#if (defined(__GNUC__) || defined(__INTEL_COMPILER) || defined(__IBMCPP__)) && !defined(__OPTIMIZE__)
+    // This violates pointer aliasing rules, but it is known to be safe (and silent)
+    // in unoptimized GCC builds (-fno-strict-aliasing). The other compilers which
+    // set the same define are assumed to be safe.
     else *reinterpret_cast<T*>(n) = t;
+#else
+    // This is always safe, but penaltizes unoptimized builds a lot.
+    else ::memcpy(n, &t, sizeof(T));
+#endif
 }
 
 template <typename T>