https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116783
--- Comment #5 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Alex Coplan <acop...@gcc.gnu.org>: https://gcc.gnu.org/g:c0e54ce1999ccf2241f74c5188b11b92e5aedc1f commit r15-4518-gc0e54ce1999ccf2241f74c5188b11b92e5aedc1f Author: Alex Coplan <alex.cop...@arm.com> Date: Fri Sep 20 17:39:39 2024 +0100 pair-fusion: Assume alias conflict if common address reg changes [PR116783] As the PR shows, pair-fusion was tricking memory_modified_in_insn_p into returning false when a common base register (in this case, x1) was modified between the mem and the store insn. This lead to wrong code as the accesses really did alias. To avoid this sort of problem, this patch avoids invoking RTL alias analysis altogether (and assume an alias conflict) if the two insns to be compared share a common address register R, and the insns see different definitions of R (i.e. it was modified in between). gcc/ChangeLog: PR rtl-optimization/116783 * pair-fusion.cc (def_walker::cand_addr_uses): New. (def_walker::def_walker): Add parameter for candidate address uses. (def_walker::alias_conflict_p): Declare. (def_walker::addr_reg_conflict_p): New. (def_walker::conflict_p): New. (store_walker::store_walker): Add parameter for candidate address uses and pass to base ctor. (store_walker::conflict_p): Rename to ... (store_walker::alias_conflict_p): ... this. (load_walker::load_walker): Add parameter for candidate address uses and pass to base ctor. (load_walker::conflict_p): Rename to ... (load_walker::alias_conflict_p): ... this. (pair_fusion_bb_info::try_fuse_pair): Collect address register uses for candidate insns and pass down to alias walkers. gcc/testsuite/ChangeLog: PR rtl-optimization/116783 * g++.dg/torture/pr116783.C: New test.
