https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104515
--- Comment #11 from GCC 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:8c67dc40459e3d72e8169b099cc8c5dbdb759da3 commit r15-2133-g8c67dc40459e3d72e8169b099cc8c5dbdb759da3 Author: Richard Biener <rguent...@suse.de> Date: Wed Jul 17 10:22:47 2024 +0200 tree-optimization/104515 - store motion and clobbers The following addresses an old regression when end-of-object/storage clobbers were introduced. In particular when there's an end-of-object clobber in a loop but no corresponding begin-of-object we can still perform store motion of may-aliased refs when we re-issue the end-of-object/storage on the exits but elide it from the loop. This should be the safest way to deal with this considering stack-slot sharing and it should not cause missed dead store eliminations given DSE can now follow multiple paths in case there are multiple exits. Note when the clobber is re-materialized only on one exit but not on anther we are erroring on the side of removing the clobber on such path. This should be OK (removing clobbers is always OK). Note there's no corresponding code to handle begin-of-object/storage during the hoisting part of loads that are part of a store motion optimization, so this only enables stored-only store motion or cases without such clobber inside the loop. PR tree-optimization/104515 * tree-ssa-loop-im.cc (execute_sm_exit): Add clobbers_to_prune parameter and handle re-materializing of clobbers. (sm_seq_valid_bb): end-of-storage/object clobbers are OK inside an ordered sequence of stores. (sm_seq_push_down): Refuse to push down clobbers. (hoist_memory_references): Prune clobbers from the loop body we re-materialized on an exit. * g++.dg/opt/pr104515.C: New testcase.
