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The following attempts to avoid IVOPTs rewriting uses using IV candidates that involve undefined behavior by using uninitialized SSA names. First we restrict the set of candidates we produce for such IVs to the original ones and mark them as not important. Second we try to only allow expressing uses with such IV if they originally use them. That is to avoid rewriting all such uses in terms of other IVs. Since cand->iv and use->iv seem to never exactly match up we resort to comparing the IV bases. The approach ends up similar to the one posted by Roger at https://gcc.gnu.org/pipermail/gcc-patches/2021-August/578441.html but it marks IV candidates rather than use groups and the cases we allow in determine_group_iv_cost_generic are slightly different. 2022-01-04 Richard Biener <rguenther@suse.de> PR tree-optimization/100810 * tree-ssa-loop-ivopts.cc (struct iv_cand): Add involves_undefs flag. (find_ssa_undef): New function. (add_candidate_1): Avoid adding derived candidates with undefined SSA names and mark the original ones. (determine_group_iv_cost_generic): Reject rewriting uses with a different IV when that involves undefined SSA names. * gcc.dg/torture/pr100810.c: New testcase. * gcc.dg/torture/pr105337.c: Likewise. |
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