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From: "helloworld922 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/63314] New: valarray mask/indices refers to temporary
Date: Fri, 19 Sep 2014 16:41:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63314

            Bug ID: 63314
           Summary: valarray mask/indices refers to temporary
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: blocker
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: helloworld922 at hotmail dot com

std::mask_array appears to be holding a reference to the underlying _M_data of
the mask std::valarray. This is a problem when the mask valarray is a
temporary:

std::valarray<int> data = {1,4,0,2,5};
std::mask_array<int> marr = data[data <= 2];

Here, the data <= 2 mask is a temporary and sarr will have an invalid address
for for the mask _M_data. Trying to do anything with mask_array at this point
would have problems, i.e.:

marr = 11;

will be undefined behavior.

Similarly, there is an identical issue with std::indirect_array:

std::indirect_array<int> iarr = data[std::valarray<size_t>({1,2,4})];

Because the underlying _M_data has no ownership in mask_array/indirect_array,
there are additional problems when trying to return the given type:

std::mask_array<int> doit(const std::valarray<int> &data)
{
    std::valarray<size_t> idx = {1,2,3};
    return data[idx];
}

It is unclear to me if this behavior is allowed by the standard, but it
certainly looks fishy, especially given that the deduced type for this:

auto marr = data[data <= 2];

is std::mask_array