r208786 - Don't copy objects with trivial, deleted copy ctors

[Reid Kleckner]

On Wed, May 14, 2014 at 4:15 PM, Richard Smith <richard at metafoo.co.uk>wrote:

> > +bool CGCXXABI::canCopyArgument(const CXXRecordDecl *RD) const {
> > +  // If RD has a non-trivial move or copy constructor, we cannot copy
> the
> > +  // argument.
> > +  if (RD->hasNonTrivialCopyConstructor() ||
> RD->hasNonTrivialMoveConstructor())
> > +    return false;
> > +
> > +  // If RD has a non-trivial destructor, we cannot copy the argument.
> > +  if (RD->hasNonTrivialDestructor())
> > +    return false;
> > +
> > +  // We can only copy the argument if there exists at least one trivial,
> > +  // non-deleted copy or move constructor.
> > +  // FIXME: This assumes that all lazily declared copy and move
> constructors are
> > +  // not deleted.  This assumption might not be true in some corner
> cases.
> > +  bool CopyOrMoveDeleted = false;
> > +  for (const CXXConstructorDecl *CD : RD->ctors()) {
> > +    if (CD->isCopyConstructor() || CD->isMoveConstructor()) {
> > +      assert(CD->isTrivial());
> > +      // We had at least one undeleted trivial copy or move ctor.
>  Return
> > +      // directly.
> > +      if (!CD->isDeleted())
> > +        return true;
> > +      CopyOrMoveDeleted = true;
> > +    }
> > +  }
> > +
> > +  // If all trivial copy and move constructors are deleted, we cannot
> copy the
> > +  // argument.
> > +  return !CopyOrMoveDeleted;
>
> This returns false if either trivial copy or move is deleted. Shouldn't we
> only return false if both of them are?
>
Is it possible to delete a copy or move constructor without forcing the
other constructors to be declared?  They appear to go together.  It's good
to be defensive though.

> > +}
>
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