https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103061
--- Comment #17 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Aldy Hernandez <al...@gcc.gnu.org>: https://gcc.gnu.org/g:4856699eeb2809c50930bafe341a96470877195d commit r12-4971-g4856699eeb2809c50930bafe341a96470877195d Author: Aldy Hernandez <al...@redhat.com> Date: Fri Nov 5 22:25:19 2021 +0100 path oracle: Do not look at root oracle for killed defs. The problem here is that we are incorrectly threading 41->20->21 here: <bb 35> [local count: 56063504182]: _134 = M.10_120 + 1; if (_71 <= _134) goto <bb 19>; [11.00%] else goto <bb 41>; [89.00%] ... ... ... <bb 41> [local count: 49896518755]: <bb 20> [local count: 56063503181]: # lb_75 = PHI <_134(41), 1(18)> _117 = mstep_49 + lb_75; _118 = _117 + -1; _119 = mstep_49 + _118; M.10_120 = MIN_EXPR <_119, _71>; if (lb_75 > M.10_120) goto <bb 21>; [11.00%] else goto <bb 22>; [89.00%] First, lb_17 == _134 because of the PHI. Second, _134 > M.10_120 because of _134 = M.10_120 + 1. We then assume that lb_75 > M.10_120, but this is incorrect because M.10_120 was killed along the path. This incorrect thread causes the miscompilation in 527.cam4_r. Tested on x86-64 and ppc64le Linux. gcc/ChangeLog: PR tree-optimization/103061 * value-relation.cc (path_oracle::path_oracle): Initialize m_killed_defs. (path_oracle::killing_def): Set m_killed_defs. (path_oracle::query_relation): Do not look at the root oracle for killed defs. * value-relation.h (class path_oracle): Add m_killed_defs.