[Bug c++/33205] New: bitfield optimizations causes corrupt bitfield expansion at runtime

[xk-corpse at hotmail dot com]

test.cxx
--
#include 

struct A
{
unsigned short x:14;
unsigned short y:14;
};


extern unsigned n;

int main()
{
A a;

a.x = n & 0x3FFF;
a.y = (n>>14) & 0x3FFF;

unsigned expected = n & 0x3FFF;

if( a.x != expected )
{
std::cout << "test failed: "
<< " (x=" << a.x
<< ") != " << expected
<< ", y=" << a.y
<< std::endl;
return 1;
}

std::cout << "test succedeed" << std::endl;

return 0;
}

unsigned n = 0xFE7B4873U;
--

output:
test failed:  (x=18547) != 2163, y=14829

14-bit unsigned field expands with non-zero padding bits


appears with gcc-4.2.1, gcc-4.1.2, gcc-4.2-20070822
does not appear with gcc-3.4.6

gcc was configured and built with crosstool-0.43 (with glibc-2.3.2)

powerpc-603-linux-gnu-g++ -v
Using built-in specs.
Target: powerpc-603-linux-gnu
Configured with:
/home/corpse/tmp/interlink/crosstool-0.43/build/powerpc-603-linux-gnu/gcc-4.2.1-glibc-2.3.2/gcc-4.2.1/configure
--target=powerpc-603-linux-gnu --host=i686-host_pc-linux-gnu
--prefix=/opt/compilers/gcc-4.2.1-glibc-2.3.2/powerpc-603-linux-gnu
--with-cpu=603 --enable-cxx-flags=-mcpu=603
--with-headers=/opt/compilers/gcc-4.2.1-glibc-2.3.2/powerpc-603-linux-gnu/powerpc-603-linux-gnu/include
--with-local-prefix=/opt/compilers/gcc-4.2.1-glibc-2.3.2/powerpc-603-linux-gnu/powerpc-603-linux-gnu
--disable-nls --enable-threads=posix --enable-symvers=gnu --enable-__cxa_atexit
--enable-languages=c,c++ --enable-shared --enable-c99 --enable-long-long
Thread model: posix
gcc version 4.2.1


-- 
   Summary: bitfield optimizations causes corrupt bitfield expansion
at runtime
   Product: gcc
   Version: 4.2.1
Status: UNCONFIRMED
  Severity: critical
      Priority: P3
 Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: xk-corpse at hotmail dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: powerpc-603-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33205

[Bug c++/33205] optimization bug: unsigned bitfield expands with non-zero padding bits

[xk-corpse at hotmail dot com]

--- Comment #1 from xk-corpse at hotmail dot com  2007-08-28 08:45 ---
i'm sorry, i forgot to say that bug appears with any optimization level enabled
(-O1, -O2, -O3) and does not appear with optimization disabled (-O0)


-- 

xk-corpse at hotmail dot com changed:

   What|Removed |Added

Summary|bitfield optimizations  |optimization bug: unsigned
   |causes corrupt bitfield |bitfield expands with non-
   |expansion at runtime|zero padding bits


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33205

[Bug target/33205] optimization bug: unsigned bitfield expands with non-zero padding bits

[xk-corpse at hotmail dot com]

--- Comment #3 from xk-corpse at hotmail dot com  2007-08-28 11:25 ---
(In reply to comment #2)
> This works for me on a x86_64 target.
> 

For me it works on i686-pc-linux (with cross-compiler, configured with the same
method as above - crosstool-0.43 + glibc-2.3.2), works on i386-mingw32 (with
cross-compiler linux->mingw32), but does not work on powerpc.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33205