https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99726
--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Richard Sandiford <rsand...@gcc.gnu.org>: https://gcc.gnu.org/g:7e2db68a77fb211898a024c5a7ad7c4449c7e355 commit r10-9749-g7e2db68a77fb211898a024c5a7ad7c4449c7e355 Author: Richard Sandiford <richard.sandif...@arm.com> Date: Fri Apr 23 10:09:38 2021 +0100 data-ref: Tighten index-based alias checks [PR99726] create_intersect_range_checks_index tries to create a runtime alias check based on index comparisons. It looks through the access functions for the two DRs to find a SCEV for the loop that is being versioned and converts a DR_STEP-based check into an index-based check. However, there isn't any reliable sign information in the types, so the code expects the value of the IV step (when interpreted as signed) to be negative iff the DR_STEP (when interpreted as signed) is negative. r10-4762 added another assert related to this assumption and the assert fired for the testcase in the PR. The sign of the IV step didn't match the sign of the DR_STEP. I think this is actually showing what was previously a wrong-code bug. The signs didn't match because the DRs contained *two* access function SCEVs for the loop being versioned. It doesn't look like the code is set up to deal with this, since it checks each access function independently and treats it as the sole source of DR_STEP. The patch therefore moves the main condition out of the loop. This also has the advantage of not building a tree for one access function only to throw it away if we find an inner function that makes the comparison invalid. gcc/ PR tree-optimization/99726 * tree-data-ref.c (create_intersect_range_checks_index): Bail out if there is more than one access function SCEV for the loop being versioned. gcc/testsuite/ PR tree-optimization/99726 * gcc.target/i386/pr99726.c: New test. (cherry picked from commit b5c7accfb56a7347008f629be4c7344dd849b1b1)
