c/6346: sign extension missing after cast down and up on long long bitfield

c/6346: sign extension missing after cast down and up on long long bitfield

[Servatius.Brandt]

>Number:         6346
>Category:       c
>Synopsis:       sign extension missing after cast down and up on long long bitfield
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Apr 18 01:56:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Servatius.Brandt@fujitsu-siemens.com
>Release:        gcc-3.0.4
>Organization:
>Environment:
sparc-sun-solaris2.8
>Description:
After converting the result of the |= operation on an
unsigned long long bitfield down to a signed char or short,
the conversion up to long long or unsigned long long forgets
the sign extension.

The problem is the same with and without optimization.
>How-To-Repeat:
gcc bug15.c && ./a.out

Output is 256, 256, 65536, 65536, -1, -1, -1, -1.
Correct output would be "-1" eigth times.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
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Re: c/6346: sign extension missing after cast down and up on long long bitfield

[neil]

Synopsis: sign extension missing after cast down and up on long long bitfield

Responsible-Changed-From-To: unassigned->neil
Responsible-Changed-By: neil
Responsible-Changed-When: Wed May 22 05:08:57 2002
Responsible-Changed-Why:
    Bitfield issues are assigned to me, though I doubt I'll
    have time to fix them until 3.3.
State-Changed-From-To: open->analyzed
State-Changed-By: neil
State-Changed-When: Wed May 22 05:08:57 2002
State-Changed-Why:
    Bitfields have several issues, fundamentally down to the
    single fact that their type is not represented properly in the
    compiler.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6346