Isn't it wasteful to first copy perhaps a large constructor (recursively)
and then truncate it to very few elts (zero in this case)?
> We should certainly avoid copying if they're the same. The code above for
> only copying the bits that aren't going to be thrown away seems pretty
> straightforward, might as well use it even if the savings aren't likely to
> be large.
Calling vec_safe_truncate with the same number of elts the vector already
has is a nop, so IMHO we just should make sure we only unshare if it
changed.
2020-03-12 Jakub Jelinek <jakub@redhat.com>
PR c++/94124
* decl.c (reshape_init_array_1): Don't unshare constructor if there
aren't any trailing zero elts, otherwise only unshare the first
nelts.
