https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107407
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Richard Biener <rgue...@gcc.gnu.org>: https://gcc.gnu.org/g:031a400e49d8db156c43f9ec0b21ab0c2aee8c6d commit r13-3546-g031a400e49d8db156c43f9ec0b21ab0c2aee8c6d Author: Richard Biener <rguent...@suse.de> Date: Fri Oct 28 15:03:49 2022 +0200 tree-optimization/107407 - wrong code with DSE So what happens is that we elide processing of this check with /* In addition to kills we can remove defs whose only use is another def in defs. That can only ever be PHIs of which we track two for simplicity reasons, the first and last in {first,last}_phi_def (we fail for multiple PHIs anyways). We can also ignore defs that feed only into already visited PHIs. */ else if (single_imm_use (vdef, &use_p, &use_stmt) && (use_stmt == first_phi_def || use_stmt == last_phi_def || (gimple_code (use_stmt) == GIMPLE_PHI && bitmap_bit_p (visited, SSA_NAME_VERSION (PHI_RESULT (use_stmt)))))) where we have the last PHI being the outer loop virtual PHI and the first PHI being the loop exit PHI of the outer loop and we've already processed the single immediate use of the outer loop PHI, the inner loop PHI. But we still have to perform the above check! It's easiest to perform the check when we visit the PHI node instead of delaying it to the actual processing loop. PR tree-optimization/107407 * tree-ssa-dse.cc (dse_classify_store): Perform backedge varying index check when collecting PHI uses rather than after optimizing processing of the candidate defs. * gcc.dg/torture/pr107407.c: New testcase.
