https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105665
--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-12 branch has been updated by Richard Biener <rgue...@gcc.gnu.org>: https://gcc.gnu.org/g:4ca164a6372412a1b3dc62b6fbde77d338e22bd4 commit r12-8624-g4ca164a6372412a1b3dc62b6fbde77d338e22bd4 Author: Alexandre Oliva <ol...@adacore.com> Date: Fri Jun 3 03:59:03 2022 -0300 [PR105665] ivopts: check defs of names in base for undefs The patch for PR 100810 tested for undefined SSA_NAMEs appearing directly in the base expression of the potential IV candidate, but that's not enough. The testcase for PR105665 shows an undefined SSA_NAME has the same ill effect if it's referenced as an PHI_NODE arg in the referenced SSA_NAME. The variant of that test shows it can be further removed from the referenced SSA_NAME. To avoid deep recursion, precompute maybe-undefined SSA_NAMEs: start from known-undefined nonvirtual default defs, and propagate them to any PHI nodes reached by a maybe-undefined arg, as long as there aren't intervening non-PHI uses, that would imply the maybe-undefined name must be defined at that point, otherwise it would invoke undefined behavior. Also test for intervening non-PHI uses of DEFs in the base expr. The test for intervening uses implemented herein relies on dominance; this could be further extended, regarding conditional uses in every path leading to a point as an unconditional use dominating that point, but I haven't implemented that. for gcc/ChangeLog PR tree-optimization/105665 PR tree-optimization/100810 * tree-ssa-loop-ivopts.cc (ssa_name_maybe_undef_p, ssa_name_set_maybe_undef): New. (ssa_name_any_use_dominates_bb_p, mark_ssa_maybe_undefs): New. (find_ssa_undef): Check precomputed flag and intervening uses. (tree_ssa_iv_optimize): Call mark_ssa_maybe_undefs. for gcc/testsuite/ChangeLog PR tree-optimization/105665 PR tree-optimization/100810 * gcc.dg/torture/pr105665.c: New. (cherry picked from commit be2861fe8c527a5952257462ceca899bb43b1452)
