Rohan:
Because no one more-authoritative has answered you,
I'll give it a try.
I think that this occurs because QVariant must have
sufficiently-strict alignment constraints to hold,
properly aligned, the largest POD datum that can be
stored in the variant. Other, more-specific objects
may be known to not have such a large POD datum
within them and so may have looser alignment
requirements.
When the more-loosely aligned object is cast to an
object type with tighter alignment constraints, the
compiler objects.
In this exact case, it doesn't look like it will hurt
you, but I think it would be good to code this in
such a way as to avoid the warning (without disabling
the warning). Unfortunately, I have no advice on how
to do this.
Atlant
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf
Of Rohan McGovern
Sent: Tuesday, March 06, 2012 18:35
To: development
Subject: [Development] cast ... increases required alignment of target type
[-Werror=cast-align]
Does anyone have a suggestion on how to fix this warning?
This code in qlist.h:
409: template <typename T>
410: Q_INLINE_TEMPLATE void QList<T>::node_destruct(Node *from, Node *to)
411: {
412: if (QTypeInfo<T>::isLarge || QTypeInfo<T>::isStatic)
413: while(from != to) --to, delete reinterpret_cast<T*>(to->v);
414: else if (QTypeInfo<T>::isComplex)
415: while (from != to) --to, reinterpret_cast<T*>(to)->~T();
416: }
...when compiled for ARM, causes this warning (or error with -Werror):
src/corelib/tools/qlist.h: In member function ‘void
QList<T>::node_destruct(QList<T>::Node*, QList<T>::Node*) [with T = QVariant]’:
src/corelib/tools/qlist.h:738:5: instantiated from ‘void
QList<T>::dealloc(QListData::Data*) [with T = QVariant]’
src/corelib/tools/qlist.h:714:9: instantiated from ‘QList<T>::~QList()
[with T = QVariant]’
src/corelib/statemachine/qstatemachine.h:81:59: instantiated from here
src/corelib/tools/qlist.h:415:28: error: cast from ‘QList<QVariant>::Node*’
to ‘QVariant*’ increases required alignment of target type [-Werror=cast-align]
"do not compile with -Wcast-align" may be a valid answer, but it would
be good to hear from someone who can confidently say whether or not this
issue can actually harm us in practice.
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