https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110515
--- Comment #11 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:9f4f833455bb35c11d03e93f802604ac7cd8b740 commit r14-2344-g9f4f833455bb35c11d03e93f802604ac7cd8b740 Author: Richard Biener <rguent...@suse.de> Date: Wed Jul 5 15:57:49 2023 +0200 tree-optimization/110515 - wrong code with LIM + PRE In this PR we face the issue that LIM speculates a load when hoisting it out of the loop (since it knows it cannot trap). Unfortunately this exposes undefined behavior when the load accesses memory with the wrong dynamic type. This later makes PRE use that representation instead of the original which accesses the same memory location but using a different dynamic type leading to a wrong disambiguation of that original access against another and thus a wrong-code transform. Fortunately there already is code in PRE dealing with a similar situation for code hoisting but that left a small gap which when fixed also fixes the wrong-code transform in this bug even if it doesn't address the underlying issue of LIM speculating that load. The upside is this fix is trivially safe to backport and chances of code generation regressions are very low. PR tree-optimization/110515 * tree-ssa-pre.cc (compute_avail): Make code dealing with hoisting loads with different alias-sets more robust. * g++.dg/opt/pr110515.C: New testcase.
