http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48973
--- Comment #6 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-05-12 09:00:59 UTC --- "Fixed" with bitfield lowering where we expand from v.0_1 = v; BF.1_3 = MEM[(struct S *)&s]; D.2700_4 = BF.1_3 & -2; D.2702_6 = v.0_1 < 0; BF.1_7 = D.2702_6 | D.2700_4; MEM[(struct S *)&s] = BF.1_7; D.2693_9 = (<unnamed-signed:1>) BF.1_7; D.2694_10 = (unsigned int) D.2693_9; if (D.2694_10 != 4294967295) similar to what Jakub proposed to do manually.