http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48973
--- Comment #9 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-05-12 11:36:21 UTC --- (In reply to comment #8) > (In reply to comment #6) > > "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. > > Well, if bitfield lowering does this and nothing cleans it up, there is room > for improvement. It would be sad if it couldn't be optimized already at the > tree level back to: > 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>) D.2702_6; // change here. Assuming D.2702 > // is either > 1 precision, or > // unsigned > D.2694_10 = (unsigned int) D.2693_9; > if (D.2694_10 != 4294967295) Yeah, we can combine that with the comparison - but I'm not sure we want to have compares with 1-bit precision quantities, do we? Or we want to optimize this to tem = D.2702_6 & CST; if (tem != 0) instead?
