c/5593: GCC miscompiles bitshifts on unsigned struct members when creating a 64-bit value

[bangerth@dealii.org]

Synopsis: GCC miscompiles bitshifts on unsigned struct members when creating a 64-bit value

State-Changed-From-To: open->analyzed
State-Changed-By: bangerth
State-Changed-When: Tue Nov  5 08:15:02 2002
State-Changed-Why:
    I can confirm this. However, I'm not sure whether what you
    do is specified at all: it all boils down to this function:
    long long equation4(struct field *data)
    {
      return ((long long)data->num << 32)|
              (data->flags << 16)|
              (data->container << 8)|
              data->quantity;
    }
    and that data->flags is a 16-bit integer. I think, shifting
    it by 16 is invoking undefined behavior, and you should
    not be surprised. But then, I'm not a language lawyer and
    leave this to someone else.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5593